Multilayer strain and stress echocardiography can represent myocardial viability and MI model types after different ischemic durations in rabbits

Multilayer strain and stress echocardiography can represent myocardial viability and MI model types after different ischemic durations in rabbits | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Multilayer strain and stress echocardiography can represent myocardial viability and MI model types after different ischemic durations in rabbits Hongyu Yang, Liping Dong, Keting Li, Zhonghui Jiang, Yujie Liu, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4149988/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background To investigate myocardial viability and MI model types using multilayer strain and stress echocardiography and evaluate the sensitive STI indicators of myocardial contractile function and viability. Methods Fifty-four rabbits were randomly divided into the 60-min, 90-min, and 120-min coronary artery occlusion groups. Blood collections and speckle tracking echocardiography (STE) were performed at baseline, after ligation, and after low-dose dobutamine stress echocardiography (LDDSE). The ratio of infarcted myocardium to viable myocardium was calculated using Evans Blue-TTC. Results After ligation, the ventricular global endocardial longitudinal strain (GSLsys-endo), global myocardial longitudinal strain (GSLsys-mid), and global epicardial longitudinal strain (GSLsys-epi) decreased in the three groups (P < 0.05); longitudinal strain of endocardium (SLsys-endo), longitudinal strain of myocardium (SLsys-mid), and longitudinal strain of epicardium (SLsys-epi) decreased in the affected segments (P < 0.05). After LDDSE, the absolute values of the above indicators in the 60-min and 90-min groups and GSLsys-endo, GSLsys-mid, GSLsys-epi in the 120-min group were significantly increased (P < 0.05). The absolute values of SLsys-endo, SLsys-mid and SLsys-epi in the ischemic segments increased (P < 0.05) in all groups. In the infarcted segments, the absolute values of SLsys-mid and SLsys-epi in 60-min group, SLsys-epi in 90-min group and none in 120-min group increased (P < 0.05). After coronary artery occlusion, malondialdehyde and tumor necrosis factor-α levels were increased, and superoxide dismutase was decreased (P < 0.05). The myocardial infarction area percentage was higher in the 120-min group (40.5%±2.8%), followed by the 90-min (29.3%±3.6%) and 60-min (16.8%±3.2%) groups (P < 0.05). The mortality of the 120-min group was higher than in the two other groups (22.2% vs. 5.6% and 11.1%, P < 0.05). Conclusions Multilayer strain and stress echocardiography can evaluate myocardial viability and MI model types in rabbits after different ischemic durations and provide insights into the selection of an appropriate STI indicators and animal model for future reperfusion experiments. speckle tracing imaging myocardial ischemia viable myocardium dobutamine stress Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Background Although the treatment of patients with ischemic heart disease (IHD) has made great progress in the past few decades[ 1 , 2 ], acute myocardial infarction is still associated with high morbidity and mortality[ 3 – 6 ]. After myocardial infarction (MI), the myocardium can be divided into the necrotic and viable myocardium areas. Viable myocardium refers to the myocardium with injury after ischemia and reperfusion but still has a contractile reserve, and its damage is reversible[ 7 ]. After MI, effective recovery of the blood perfusion is the key to saving the cardiac muscle[ 8 , 9 ]. Nevertheless, there is a possibility of recovery only if there is a viable myocardium in the affected area[ 10 , 11 ]. Therefore, the early evaluation of myocardial viability and functional reserve is critical for patient prognosis[ 11 , 12 ]. Low-dose dobutamine stress echocardiography (LDDSE) is currently recognized as an effective technique for evaluating myocardial viability. The viable myocardium can be determined by evaluating the changes in wall motion before and after stress[ 13 ]. LDDSE has a wide range of clinical applications, predictable side effects and is consistent with coronary angiography and positron emission tomography (PET) results[ 14 ]. Nevertheless, the assessment of abnormal wall motion is semi-quantitative and subjective, leading to a low consistency among observers[ 13 ]. Therefore, obtaining quantitative local myocardial deformation parameters is necessary to achieve an objective evaluation. Speckle tracking imaging (STI) is based on high frame rate two-dimensional gray-scale ultrasound images, which track the spatial motion of echogenic spots in the myocardium in real-time, without subjective influence from the examiner, without angle dependence, and with high reproducibility[ 15 , 16 ]. STI can accurately evaluate left ventricular global and regional myocardial function[ 16 ]. STI divides the myocardium into the endocardium, myocardium, and epicardium for functional evaluation. It can evaluate the overall and local myocardial strain function in a multi-faceted manner, understand the progress of the disease, and detect myocardial damage or improvement earlier[ 17 , 18 ]. The situation provides a new quantitative means for comprehensive evaluation of cardiac mechanics movement. Still, the best STI parameters to predict recovery are unknown. This animal study aimed to represent myocardial viability and MI model types using multilayer strain and stress echocardiography and evaluate the sensitive STI indicators of myocardial contractile function and viability after ischemia and LDDSE. The results could provide insights into the selection of an appropriate STI indicators and animal model for future reperfusion experiments. Methods Animals This study was carried out in strict accordance with the ARRIVE guidelines. The protocol was approved by the Committee on the animal ethics committee of the Affiliated Obstetrics and Gynecology Hospital of Tongji University. Our study is reported in accordance with ARRIVE guidelines. All possible means were taken to minimize suffering. Five-four healthy Japanese white rabbits were provided by the Animal Experimental Center of the Affiliated Obstetrics and Gynecology Hospital of Tongji University, males and females weighing 2.2–3.2 kg. Model Establishment A multi-lead electrocardiogram (ECG) was recorded during model establishment. The rabbits were anesthetized with 3% phenobarbital sodium through the ear vein. The rabbits were kept in a natural breathing state. They were fixed on the operating table on their back. The skin was prepared. The chest was opened along the midline, and the heart was exposed layer by layer. The left atrial appendage was pinched to pull the heart. A small round needle was used to pass through the superficial myocardium about 3 mm below the left atrial appendage. A suture was used to block the left ventricular branch of the coronary artery. At the same time, a thin wire was placed in the suture for repeated ligation-reperfusion. The color of the anterior wall and apex of the left ventricle was observed to become lighter, and the pulsation weakened. The ST segment was significantly uplifted in more than two limbs or the chest lead, indicating that the left ventricular branch was successfully ligated. Grouping The 54 rabbits were randomly divided into three groups (n = 18/group): coronary artery occlusion for 60 min, coronary artery occlusion for 90 min, and coronary artery occlusion for 120 min. Each group of rabbits underwent LDDSE examination after blocking. Dobutamine was evenly pumped using a microinfusion pump at a starting dose of 5 µg/kg/min and increased to 10 µg/kg/min after 5 min. After 5 min, the drug was stopped, and the general reaction and heart rate of the rabbit were observed. Echocardiography was performed before and after coronary artery occlusion and after pumping dobutamine at 10 µg/kg/min. Blood (3 ml) was sampled from the rabbit ear vein and stored in a test tube. Two-dimensional echocardiography and STI A GE Vivid7 Dimension color Doppler ultrasound system with a 10s probe (frequency of 4.4–11.4 MHz) (GE Healthcare, Waukesha, WI, USA) and an EchoPAC external digital ultrasound workstation equipped with STI post-processing software (GE Healthcare, Waukesha, WI, USA) were used in this study. Left ventricular end-diastolic diameter (LVDd), left ventricular end-systolic diameter (LVDs), left ventricular ejection fractions (LVEF), and heart rate were measured. Two-dimensional gray-scale dynamic images of three cardiac cycles with continuous heart rhythm stability with the long axis of the apex (four-chamber, two-chamber, three-chamber) were collected, ensuring clear intracardiac and adventome, frame rate > 110 frames/s. All images were transferred into the EchoPAC external workstation. The region of interest (ROI) myocardial range was selected. The myocardial intimal curve was delineated, and the width of the ROI was adjusted. The system automatically analyzed each segment. “√” stood for a successful segment, while “×” stood for an unsuccessful segment. The system accepted “√” segments and automatically displayed the strain and strain rate graphs for each segment. The longitudinal systolic strain (SLsys) of the left ventricle segments was recorded, including subendocardial, myocardial, and subepicardial systolic strains (SLsys-endo, SLsys-mid, and SLsys-epi, respectively) and left ventricular global longitudinal systolic strain (GSIsys), including subendocardial, myocardium, and subepicardial systolic strains (GSLsys-endo, GSLsys-mid, and GSLsys-epi, respectively). Detection of the concentration of malondialdehyde (MDA), superoxide dismutase (SOD), and tumor necrosis factor (TNF)-α in peripheral blood Radioimmunoassay and enzyme labeling methods were used to measure MDA, SOD, and TNF-α according to the manufacturers’ instructions (Bohu Institute of Biotechnology, Shanghai, China. Histology At the end of the experiment, the rabbits were sacrificed by air embolization of the ear vein. The left ventricle branch was re-ligated. Then, 10 ml of Evans blue dye was injected into the coronary artery through the aorta. After the hearts were stained blue, they were washed with physiological saline. After being frozen at -20°C for 15 min, the hearts were cut into 2-mm-thick sections and immersed in 2% TTC buffer at 37°C for 20 min. After staining, the sections were fixed in 10% formaldehyde. The myocardial infarct area, ischemic area, and left ventricular muscle area were analyzed using Image-Pro Plus 7.0 (Media Cybernetics, Inc., Rockville, MD, USA). The percentage of the infarcted myocardial area was calculated. The changes in myocardial color in each segment of the left ventricle were observed. Based on the 16-segment method recommended by the American Ultrasound Association, the viable myocardium in the necrotic zone was identified based on the staining results, and the number of segments was calculated. The infarct area was grey, the ischemic area was red, and the normal area was blue. If necrosis was observed in > 50% of a given segment, the segment was considered non-viable (infarcted segment)[ 19 ]. Otherwise, it was considered viable (ischemic segment). Statistical analysis All analyses were performed using SPSS 26.0 (IBM, Armonk, NY, USA). Continuous data with normal distributions were expressed as the mean ± standard deviation (SD). Numerical data were tested for normal distribution using the Kolmogorov-Smirnov test. All data were analyzed using analysis of variance (ANOVA) and the LSD post hoc test. Time-point variables in echocardiographic measurements were compared using repeated measure ANOVA followed by the Student-Newman-Keuls post hoc test. P-values < 0.05 were considered statistically significant. Results Animal model There were seven (12.9%) deaths among the 54 rabbits: one deaths in the 60-min groups (mortality of 5.6%), two in 90-min groups (mortality of 11.1%) and four in 120-min group (mortality of 22.2%). After staining, the infarcted area was grayish-white, the ischemic area was brick red, and the non-ischemic area was blue (Fig. 1 ). The myocardial infarction area percentage was higher in the 120-min group (40.5%±2.8%), followed by the 90-min (29.3%±3.6%) and 60-min (16.8%±3.2%) groups ( P < 0.05). In the 60-min group, 272 segments in 17 rabbits were evaluated, including 207 (76.1%) segments of non-ischemic myocardium, 46 (16.9%) ischemic segments with viable myocardium, and 19 (7.0%) infarcted segments with non-viable myocardium. In the 90-min group, there were 189 (73.8%) non-ischemic segments, 38 (14.9%)ischemic and 29 (11.3%) infarcted segments in 256 evaluated segments of 16 rabbits. In the 120-min group, 155 (69.2%) non-ischemic segments, 35 (15.6%) ischemic and 34 (15.2%) infarcted segments in 224 segments of 14 rabbits. Longitudinal strain between ischemic and infarcted segments after coronary artery ligation and LDDSE After ligation, the absolute values of SLsys-endo, SLsys-mid, and SLsys-epi were significantly lower in the ischemic segments and infarcted segments compared with the baseline levels (all P 0.05) (Table 1 ). After LDDSE, the absolute values of SLsys-endo, SLsys-mid and SLsys-epi in the ischemic segments were higher than after ligation ( P < 0.05) in all groups. In the infarcted segments, the absolute values of SLsys-mid and SLsys-epi in 60-min group and SLsys-epi in 90-min group were higher than after ligation ( P 0.05) (Table 1 ). Table 1 Longitudinal strain between ischemic segments and infarcted segments after ligation and dobutamine stress in rabbits the 60-min Group the 90-min Group the 120-min Group n SLsys-endo (%) SLsys-mid (%) SLsys-epi (%) n SLsys-endo (%) SLsys-mid (%) SLsys-epi (%) n SLsys-endo (%) SLsys-mid (%) SLsys-epi (%) Baseline Ischemic segments 46 -16.2 ± 3.7 -15.3 ± 3.3 -12.5 ± 2.7 38 -14.9 ± 3.1 -12.7 ± 3.2 -11.1 ± 2.8 35 -15.5 ± 3.5 -13.6 ± 3.9 -12.3 ± 3.7 Infarcted segments 19 -15.1 ± 2.9 -14.8 ± 3.6 -12.6 ± 3.5 29 -15.7 ± 3.8 -13.3 ± 3.5 -11.5 ± 3.4 34 -14.8 ± 3.8 -13.4 ± 3.3 -11.6 ± 3.4 After ligation Ischemic segments 46 -10.5 ± 4.1 a -9.1 ± 5.1 a -7.6 ± 3.4 a 38 -9.3 ± 4.5 a -8.5 ± 4.4 a -6.8 ± 4.2 a 35 -8.2 ± 4.0 a -7.5 ± 4.1 a -5.7 ± 3.2 a Infarcted segments 19 -7.3 ± 4.6 a -6.7 ± 4.9 a -4.9 ± 4.8 a 29 -6.6 ± 3.7 a -5.7 ± 3.8 a -3.5 ± 3.1 a 34 -5.6 ± 3.7 a -4.7 ± 3.9 a -3.9 ± 4.2 a After LDDSE Ischemic segments 46 -14.5 ± 4.5 b -13.5 ± 3.7 b -11.8 ± 4.8 b 38 -12.8 ± 3.9 b -11.5 ± 3.3 b -9.9 ± 4.1 b 35 -13.2 ± 3.7 b -11.5 ± 3.1 b 10.1 ± 3.8 b Infarcted segments 19 -9.8 ± 3.0 -9.9 ± 4.3 c -8.1 ± 3.9 c 29 -6.9 ± 3.8 -6.9 ± 4.2 -6.1 ± 3.6 c 34 -5.8 ± 3.0 -4.9 ± 4.2 -4.1 ± 3.8 a P < 0.05 vs. baseline within each group; b P < 0.05 vs. after ligation within each group; c P < 0.05 vs. Infarcted segments after ligation. SLsys-endo: longitudinal systolic strain in endocardium; SLsys-mid: longitudinal systolic strain in midmyocardium; SLsys-epi: longitudinal systolic strain in the epicardium. Data are presented as mean ± standard deviation. Changes in the left ventricular longitudinal strain at baseline and after coronary artery ligation and LDDSE in each group After coronary artery ligation, the absolute values of GSLsys-endo, GSLsys-mid, GSLsys-epi and SLsys-endo, SLsys-mid, and SLsys-epi in the affected segments were significantly lower than at baseline (all P < 0.05). After LDDSE, the absolute values of the above indicators in the 60-min and 90-min groups and GSLsys-endo, GSLsys-mid, GSLsys-epi in the 120-min group were significantly increased compared with those after ligation, and the differences were statistically significant (all P < 0.05). But, the affected segmental SLsys-endo, SLsys-mid, and SLsys-epi in the 120-min group were similar compared with those after ligation (Table 2 and Figs. 3 – 5 ). Table 2 Left ventricular longitudinal strain at baseline and after coronary artery ligation and dobutamine stress in rabbits n rabbits GSLsys-endo (%) GSLsys-mid (%) GSLsys-epi (%) SLsys-endo (%) SLsys-mid (%) SLsys-epi (%) 60 min Baseline 18 -17.4 ± 3.1 -14.1 ± 2.5 -11.3 ± 3.2 -14.9 ± 2.8 -10.9 ± 2.9 -7.8 ± 3.2 After ligation 17 -12.8 ± 3.5 c -10.6 ± 2.5 c -8.2 ± 2.3 c -7.2 ± 2.8 c -5.7 ± 3.0 c -3.5 ± 2.7 c After LDDSE 17 -16.1 ± 3.8 d -13.8 ± 3.0 d -10.9 ± 2.7 d -11.5 ± 3.2 d -9.2 ± 2.8 d -5.8 ± 2.5 d 90 min Baseline 18 -18.1 ± 3.5 -14.4 ± 3.4 -10.7 ± 3.1 -14.3 ± 3.1 -11.5 ± 3.0 -8.3 ± 2.8 After ligation 16 -8.1 ± 2.3 ac -7.2 ± 2.0 ac -6.4 ± 2.2 c -4.5 ± 2.7 ac -3.9 ± 2.9 ac -2.9 ± 3.0 c After LDDSE 16 -13.7 ± 3.2 d -11.1 ± 2.4 d -9.5 ± 2.7 d -8.9 ± 3.1 d -6.5 ± 2.6 ad -4.9 ± 3.1 d 120 min Baseline 18 -18.3 ± 2.9 -13.7 ± 3.6 -10.5 ± 2.7 -15.1 ± 3.1 -12.1 ± 3.2 -8.7 ± 3.3 After ligation 14 -5.4 ± 1.9 abc -4.3 ± 2.6 abc -3.2 ± 2.3 abc -2.3 ± 2.8 abc -1.9 ± 3.0 abc -1.2 ± 2.9 abc After LDDSE 14 -9.6 ± 2.4 abd -7.2 ± 2.7 abd -6.6 ± 2.9 abd -4.0 ± 2.9 ab -3.4 ± 3.0 ab -1.5 ± 2.4 ab a P < 0.05 vs. 60 min; b P < 0.05 vs. 90 min; c P < 0.05 vs. baseline within each group; d P < 0.05 vs. after coronary artery ligation within each group. GSLsys-endo: global longitudinal systolic strain in endocardium; GSLsys-mid: global longitudinal systolic strain in midmyocardium; GSLsys-epi: global longitudinal systolic strain in epicardium; SLsys-endo: SLsys-endo: longitudinal systolic strain in endocardium; SLsys-mid: longitudinal systolic strain in midmyocardium; SLsys-epi: longitudinal systolic strain in the epicardium. Data are presented as mean ± standard deviation. Comparison of longitudinal strains at baseline and after coronary artery ligation and LDDSE among groups At baseline, there were no significant differences among the three groups regarding GSLsys and local SLsys (all P > 0.05). After coronary artery ligation, the GSLsys-endo, GSLsys-mid, GSLsys-epi and the affected segmental SLsys-endo, SLsys-mid, SLsys-epi in the 120-min group were significantly lower than the 60-min and 90-min groups. The GSLsys-endo, GSLsys-mid and affected segmental SLsys-endo and SLsys-mid in the 90-min group were lower than the 60-min group (all P 0.05). After LDDSE, the values of GSLsys-endo, GSLsys-mid, GSLsys-epi, SLsys-endo, SLsys-mid, and SLsys-epi in the 120-min group were significantly lower compared with the 60-min and 90-min groups (Table 2 ). MDA, SOD, and TNF-α before and after coronary artery ligation and LDDSE in each group At baseline, there were no significant differences among the three groups in MDA levels (all P > 0.05). After ligation and LDDSE, the differences among the three groups were statistically significant (all P < 0.05). The MDA levels were significantly increased after ligation compared with baseline levels (all P < 0.05). The MDA content was decreased after LDDSE in the 90-min and 120-min groups (all P < 0.05) (Table 3 ). Table 3 Serum MDA, SOD, and TNF-α at baseline and after coronary artery ligation and dobutamine stress in rabbits n rabbits MDA (nmol/ml) SOD (U/ml) TNF-α (pg/ml) 60 min Baseline 18 7.40 ± 0.71 24.10 ± 1.45 22.56 ± 5.19 After ligation 17 9.71 ± 0.85 c 20.62 ± 1.27 c 38.20 ± 7.27 c After dobutamine stress 17 8.28 ± 0.79 22.97 ± 1.61 d 31.79 ± 6.65 d 90 min Baseline 18 7.14 ± 0.51 23.42 ± 1.96 21.77 ± 6.81 After ligation 16 13.32 ± 0.63 ac 18.74 ± 1.78 c 60.54 ± 8.18 ac After dobutamine stress 16 10.76 ± 0.77 ad 19.65 ± 1.55 49.50 ± 7.72 ad 120 min Baseline 18 7.22 ± 0.68 25.13 ± 1.63 20.57 ± 6.69 After ligation 14 17.49 ± 0.72 abc 15.17 ± 1.75 abc 74.47 ± 7.53 abc After dobutamine stress 14 14.60 ± 0.83 abd 18.23 ± 1.88 ad 60.60 ± 7.94 abd a P < 0.05 vs. 60 min; b P < 0.05 vs. 90 min; c P < 0.05 vs. baseline within each group; d P < 0.05 vs. after coronary artery ligation within each group. MDA: malondialdehyde; SOD: superoxide dismutase; TNF-α: tumor necrosis factor-α. Data are presented as mean ± standard deviation. At baseline, there were no significant differences among the three groups in SOD levels (all P > 0.05). After ligation, the differences between the 60-min and 120-min groups were statistically significant (all P < 0.05), and the content of SOD was decreased. Compared with after ligation, SOD levels in the 120-min group increased after LDDSE ( P 0.05). After ligation and LDDSE, the difference among the three groups were significantly different (all P < 0.05), significantly increased after ligation (all P < 0.05), and decreased after LDDSE compared with after ligation (all P < 0.05) (Table 3 ). Discussion The viable myocardium is the myocardium with reversible myocardial injury and contractile reserve. In most previous studies, viable myocardium was assessed by establishing a myocardial ischemia-reperfusion model, often overlooking the presence of viable myocardium after coronary ischemia. After reperfusion, there is no reliable basis for the recovery of some myocardial function. This study aimed to represent myocardial viability and evaluate the reliable and sensitive multilayer strain and stress echocardiography indicators of myocardial contractile function and viability after ischemia and LDDSE. The results suggest that layer-specific strain of STI combined with LDDSE can accurately evaluate the changes in myocardial systolic function and viability in rabbits with different ischemic durations. These could provide insights into the selection of an appropriate STI indicators for future reperfusion experiments. These results are supported by Ben DA et al.[ 20 ]. Myocardial viability is different according to ischemic time[ 20 , 21 ], but there are few studies on myocardial viability and myocardial function reserve after different ischemic times. Studies showed that ischemia could lead to coronary microvascular dysfunction, and the degree of damage is affected by the duration of ischemia[ 22 , 23 ]. The ischemic myocardium has more lactic acid production, which increases with the increase of ischemia time. In this study, the number of viable myocardium segments decreased with increasing blocking time. The GSLsys-endo, GSLsys-mid, GSLsys-epi, and blocking segments of SLsys-endo, SLsys-mid, and SLsys-epi in the 120-min group with fewer viable myocardium segments were significantly lower than in the 60-min and 90-min groups, suggesting that different blocking times may have different effects on the mechanical function of the viable myocardium. In recent years, with the deepening of research on the mechanism of cardiovascular disease, some studies have found that oxidative stress is closely related to the occurrence and development of various cardiovascular diseases, which may be one of the common mechanisms of cardiovascular disease and play a certain role in the course of atherosclerosis[ 24 , 25 ]. SOD is one of the oxygen free radical scavengers in the body, reducing the damage of oxygen free radicals on cells[ 26 ]. Its activity can be used to assess the degree of oxygen free radical scavenging ability. MDA is a product of lipid peroxidation, and its amount can reflect the degree of oxidative stress in the body[ 27 ]. In this study, with the increase of coronary artery occlusion time, the activity of SOD decreased, and the activity of MDA increased, indicating that the ability of cardiomyocytes to scavenge oxygen free radicals decreased and the oxidative stress response increased with the increase of ischemia time, also reflecting the degree of ischemia and hypoxia in cells[ 28 ]. In addition, studies showed that active inflammatory reaction in atherosclerotic plaques might be another important risk factor for the increasing severity of coronary heart disease[ 29 ]. TNF-α is an important inflammatory cytokine and plays an important role in inducing local adhesion, aggregation, activation, and damage of inflammatory cells. In this study, with the increase of coronary artery occlusion time, the TNF-α content of rabbits in each group increased significantly. This phenomenon might be caused by an increase in reactive oxygen species due to the action of inflammatory cytokines after acute myocardial infarction. In turn, the increase in reactive oxygen species increases myocardial damage, which leads to a vicious circle that further aggravates myocardial damage over time. Szymczyk et al. [ 30 ]considered that the absolute value of the longitudinal strain has a higher prediction probability for the corresponding contraction reserve of the viable myocardium, and the larger the absolute value of the longitudinal strain may correspond to a better reserve function. In this study, the absolute value of GSLsys in each layer of the left ventricle and SLsys-endo, SLsys-mid, and SLsys-epi of the viable myocardium after LDDSE were increased in all groups. However, in the infarcted segments, the absolute values of SLsys-mid and SLsys-epi in 60-min group and SLsys-epi in 90-min group were higher than after ligation. And there were no significant differences in SLsys-endo of 60-min group, SLsys-endo and SLsys-mid of 90-min group and all of 120-min group in infarcted segments after LDDSE. These indicated that it was transmural myocardial infarction in the 120-min group and subendocardial myocardial infarction in the 60-min group. And this was also confirmed by histopathological findings. The GSLsys and the affected segmental SLsys in the 120-min group were significantly lower than in the other two groups after ligation and LDDSE. The probability of ventricular fibrillation in rabbits increased significantly during the experiment, and mortality increased consequently. Therefore, after comprehensive consideration, we may prefer to use the 90-min coronary artery occlusion model as the next acute infarction reperfusion animal model. So the multilayer strain and stress echocardiography may represent myocardial viability in different layers and MI model types in rabbits. The results could help in the selection of an appropriate animal model for future reperfusion experiments. In the present study, the viability and functional reserve of myocardium after different ischemic durations by multilayer strain and stress echocardiography, which can reflect the changes of whole and local myocardial function and myocardial cell damage before and after coronary artery occlusion. This technique is non-invasive, objective, and not affected by the operator, which is more suitable for clinical use[ 18 ]. The changes of SLsys-endo under the endometrium were the most pronounced and consistent with pathological findings. So SLsys-endo could refer as the indicator to early detect the subendocardial myocardial ischemia and infarction. This study has limitations. First, the number of animals included in this study was limited. The results of this study should be confirmed by a larger sample size study. STI stratified strain requires a high frame rate and clear display of the ventricular endocardium, myocardium, and epicardium, which requires high image quality, but some images were unclear due to the rapid heart rate of rabbits. Rabbit anatomy and coronary angiography are similar to humans, but there are still differences. Conclusions In conclusion, with the increase of coronary artery occlusion time, the infarcted myocardium increased, and the myocardial viability, the functional reserve of viable myocardium, and the systolic function decreased. Combined with LDDSE, STI can accurately assess myocardial viability and contractile reserve changes at different ischemic times. This study could provide insights into the selection of an appropriate STI indicators and animal model for future reperfusion experiments. Declarations Acknowledgements Not applicable. Authors’ contributions YHY and DLP contributed equally to the article. YHY and DLP were responsible for the substantial contributions to the conception, design of the work and drafted the work, JZH analysised and interpreted the data, LKT contributed to the conception of the manuscript, RM and LYJ were responsible for the modification of language. DLP was responsible for substantial contributions to the conception, revision of the work, and ensure that all listed authors have approved the manuscript before submission. Funding No funding. Data Availability Some of the data that support the findings of this study are available from the Second Affiliated Hospital of Harbin Medical University but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. If someone wants to request the data from our study, data are available from the Min Ren（ [email protected] ）upon reasonable request and with permission of the Second Affiliated Hospital of Harbin Medical University. Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests The authors declare that they have no competing interests. Ethics approval and consent to participate The study was approved by the animal ethics committee of the Affiliated Obstetrics and Gynecology Hospital of Tongji University（TJBG03324201）. Author details 1 Department of Ultrasound Medicine, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai 200092, China. 2 Department of Ultrasound Medicine, The Sixth People's Hospital Affiliated to Shanghai Jiao Tong University, Shanghai 201306, China. 3 Department of Ultrasound Medicine, The Second Affiliated Hospital of Harbin Medical University, Harbin 150086, China. 4 Department of Ultrasound Medicine, Sanya Central Hospital (Hainan Third People’s Hospital), Sanya 572000, China. 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Anavekar NS, Chareonthaitawee P, Narula J, Gersh BJ: Revascularization in Patients With Severe Left Ventricular Dysfunction: Is the Assessment of Viability Still Viable? J Am Coll Cardiol 2016, 67 (24):2874-2887. Panza JA, Chrzanowski L, Bonow RO: Myocardial Viability Assessment Before Surgical Revascularization in Ischemic Cardiomyopathy: JACC Review Topic of the Week . J Am Coll Cardiol 2021, 78 (10):1068-1077. Park S, Ahn JM, Kim TO, Park H, Kang DY, Lee PH, Jeong YJ, Hyun J, Lee J, Kim JH et al : Revascularization in Patients With Left Main Coronary Artery Disease and Left Ventricular Dysfunction . J Am Coll Cardiol 2020, 76 (12):1395- 1406. Zhao BH, Ruze A, Zhao L, Li QL, Tang J, Xiefukaiti N, Gai MT, Deng AX, Shan XF, Gao XM: The role and mechanisms of microvascular damage in the ischemic myocardium . Cell Mol Life Sci 2023, 80 (11):341. He J, Bellenger NG, Ludman AJ, Shore AC, Strain WD: Treatment of myocardial ischaemia-reperfusion injury in patients with ST-segment elevation myocardial infarction: promise, disappointment, and hope . Rev Cardiovasc Med 2022, 23 (1):23. Wu S, Chang G, Gao L, Jiang D, Wang L, Li G, Luo X, Qin S, Guo X, Zhang D: Trimetazidine protects against myocardial ischemia/reperfusion injury by inhibiting excessive autophagy . J Mol Med (Berl) 2018, 96 (8):791-806. Lin Y, Guan X, Ren K, Zhu Y, Lu Y, Shang Y: Low-dose dobutamine stress myocardial contrast echocardiography for the evaluation of myocardial microcirculation and prediction of overall cardiac function recovery . Exp Ther Med 2020, 20 (2):1315-1320. Bautz J, Stypmann J, Reiermann S, Pavenstadt HJ, Suwelack B, Stegger L, Rahbar K, Reuter S, Schafers M: Prognostic implication of myocardial perfusion and contractile reserve in end-stage renal disease: A direct comparison of myocardial perfusion scintigraphy and dobutamine stress echocardiography . J Nucl Cardiol 2022, 29 (6):2988-2999. Morariu VI, Arnautu DA, Morariu SI, Popa AM, Parvanescu T, Andor M, Abhinav S, David VL, Ionescu A, Tomescu MC: 2D speckle tracking: a diagnostic and prognostic tool of paramount importance . Eur Rev Med Pharmacol Sci 2022, 26 (11):3903-3910. Badano LP, Kolias TJ, Muraru D, Abraham TP, Aurigemma G, Edvardsen T, D'Hooge J, Donal E, Fraser AG, Marwick T et al : Standardization of left atrial, right ventricular, and right atrial deformation imaging using two-dimensional speckle tracking echocardiography: a consensus document of the EACVI/ASE/Industry Task Force to standardize deformation imaging . Eur Heart J Cardiovasc Imaging 2018, 19 (6):591-600. Coiro S, Huttin O, Bozec E, Selton-Suty C, Lamiral Z, Carluccio E, Trinh A, Fraser AG, Ambrosio G, Rossignol P et al : Reproducibility of echocardiographic assessment of 2D-derived longitudinal strain parameters in a population-based study (the STANISLAS Cohort study) . Int J Cardiovasc Imaging 2017, 33 (9):1361- 1369. Rong LQ, Yum B, Abouzeid C, Palumbo MC, Brouwer LR, Devereux RB, Girardi LN, Weinsaft JW, Gaudino M, Kim J: Echocardiographic predictors of intraoperative right ventricular dysfunction: a 2D and speckle tracking echocardiography study . Cardiovasc Ultrasound 2019, 17 (1):11. Bonner BP, Yurista SR, Coll-Font J, Chen S, Eder RA, Foster AN, Nguyen KD, Caravan P, Gale EM, Nguyen C: Contrast-Enhanced Cardiac Magnetic Resonance Imaging With a Manganese-Based Alternative to Gadolinium for Tissue Characterization of Acute Myocardial Infarction . J Am Heart Assoc 2023, 12 (8):e026923. Ben Driss A, Ben Driss Lepage C, Sfaxi A, Hakim M, Elhadad S, Tabet JY, Salhi A, Brandao Carreira V, Hattab M, Meurin P et al : Strain predicts left ventricular functional recovery after acute myocardial infarction with systolic dysfunction . Int J Cardiol 2020, 307 :1-7. Dauerman HL, Ibanez B: The Edge of Time in Acute Myocardial Infarction . J Am Coll Cardiol 2021, 77 (15):1871-1874. Stahli BE, Varbella F, Linke A, Schwarz B, Felix SB, Seiffert M, Kesterke R, Nordbeck P, Witzenbichler B, Lang IM et al : Timing of Complete Revascularization with Multivessel PCI for Myocardial Infarction . N Engl J Med 2023, 389 (15):1368-1379. Westergren HU, Michaelsson E, Blomster JI, Miliotis T, Svedlund S, Gan LM: Determinants of coronary flow reserve in non-diabetic patients with chest pain without myocardial perfusion defects . PLoS One 2017, 12 (4):e0176511. Ndrepepa G: Myeloperoxidase - A bridge linking inflammation and oxidative stress with cardiovascular disease . Clin Chim Acta 2019, 493 :36-51. Steven S, Frenis K, Oelze M, Kalinovic S, Kuntic M, Bayo Jimenez MT, Vujacic-Mirski K, Helmstadter J, Kroller-Schon S, Munzel T et al : Vascular Inflammation and Oxidative Stress: Major Triggers for Cardiovascular Disease . Oxid Med Cell Longev 2019, 2019 :7092151. Ali SS, Ahsan H, Zia MK, Siddiqui T, Khan FH: Understanding oxidants and antioxidants: Classical team with new players . J Food Biochem 2020, 44 (3):e13145. Zhang J, Yang Z, Zhang S, Xie Z, Han S, Wang L, Zhang B, Sun S: Investigation of endogenous malondialdehyde through fluorescent probe MDA-6 during oxidative stress . Anal Chim Acta 2020, 1116 :9-15. Wu F, Ye B, Wu X, Lin X, Li Y, Wu Y, Tong L: Paeoniflorin on Rat Myocardial Ischemia Reperfusion Injury of Protection and Mechanism Research . Pharmacology 2020, 105 (5-6):281-288. Dugani SB, Moorthy MV, Li C, Demler OV, Alsheikh-Ali AA, Ridker PM, Glynn RJ, Mora S: Association of Lipid, Inflammatory, and Metabolic Biomarkers With Age at Onset for Incident Coronary Heart Disease in Women . JAMA Cardiol 2021, 6 (4):437-447. Szymczyk E, Lipiec P, Michalski B, Szymczyk K, Shim A, Wozniakowski B, Rotkiewicz A, Stefanczyk L, Kasprzak JD: 2D speckle tracking echocardiography for the assessment of regional contractile reserve after myocardial infarction . J Cardiovasc Med (Hagerstown) 2016, 17 (5):374-381. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4149988","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":288355179,"identity":"859388d1-b01c-4233-bf52-90a28f8dfe5c","order_by":0,"name":"Hongyu Yang","email":"","orcid":"","institution":"Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, China","correspondingAuthor":false,"prefix":"","firstName":"Hongyu","middleName":"","lastName":"Yang","suffix":""},{"id":288355180,"identity":"425a4bbc-e460-4caf-b6bf-79ffa323f081","order_by":1,"name":"Liping Dong","email":"","orcid":"","institution":"The Sixth People's Hospital, Shanghai Jiao Tong University","correspondingAuthor":false,"prefix":"","firstName":"Liping","middleName":"","lastName":"Dong","suffix":""},{"id":288355181,"identity":"57d32d86-0955-46ec-a460-1c93bdcc61f3","order_by":2,"name":"Keting Li","email":"","orcid":"","institution":"Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, China","correspondingAuthor":false,"prefix":"","firstName":"Keting","middleName":"","lastName":"Li","suffix":""},{"id":288355183,"identity":"f1e070f2-2721-4296-8dd4-6213e51f54f0","order_by":3,"name":"Zhonghui Jiang","email":"","orcid":"","institution":"The Second Affiliated Hospital of Harbin Medical University","correspondingAuthor":false,"prefix":"","firstName":"Zhonghui","middleName":"","lastName":"Jiang","suffix":""},{"id":288355190,"identity":"49992086-7a0e-4104-a8d9-772eefe0a019","order_by":4,"name":"Yujie Liu","email":"","orcid":"","institution":"Sanya Central Hospital (Hainan Third People’s Hospital)","correspondingAuthor":false,"prefix":"","firstName":"Yujie","middleName":"","lastName":"Liu","suffix":""},{"id":288355192,"identity":"d15dc8de-cecd-4d54-8c76-90e9d29b6464","order_by":5,"name":"Min Ren","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyElEQVRIiWNgGAWjYLCCBAYbHjb25gMHPvwgXkuaHD/PscSDM3uIt+ewseQMH+PDHGxEqDVv7z264eEO5sQNN3g+HGbgYZDnFzuAX4vMmXNpNxLPsCVuuN274XCBBYPhzNkJ+LVISOSY3Uhs40nccOfshsMzeBgSDG4T0iL/BqRFAuiwnAeHediI0SLBA9JiAPR+DgORWnjADksABbIBMJAliPAL+xmzmz/b/oOi8vGHDz9s5PmlCWjBMII05aNgFIyCUTAKsAMAJnxJagv+0mMAAAAASUVORK5CYII=","orcid":"","institution":"Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, China","correspondingAuthor":true,"prefix":"","firstName":"Min","middleName":"","lastName":"Ren","suffix":""}],"badges":[],"createdAt":"2024-03-22 13:07:55","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4149988/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4149988/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54360404,"identity":"8d7beab8-ecbb-4a00-9012-1b8f88b5fbae","added_by":"auto","created_at":"2024-04-09 11:00:00","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":90230,"visible":true,"origin":"","legend":"\u003cp\u003eGross specimens of myocardial tissue stained with TTC-Evans Blue. Infarcted myocardium is grayish-white, ischemic myocardium is bricking red, normal myocardium is blue. A. 60 min. B. 90 min. C. 120 min.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4149988/v1/99931d2bf4fb4cfe5459429c.jpg"},{"id":54360405,"identity":"8d454931-5482-4b0b-afaf-9a29478beb80","added_by":"auto","created_at":"2024-04-09 11:00:00","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":191627,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative images of longitudinal strain curves afterligation. Each section of the curve was smooth and located below the baseline, while the peak of the longitudinal strain curve was high.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4149988/v1/9a3fcf507fc11a5476dc174d.jpg"},{"id":54360408,"identity":"c3a21e40-f36a-4e63-b408-6d7f46556124","added_by":"auto","created_at":"2024-04-09 11:00:00","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":316305,"visible":true,"origin":"","legend":"\u003cp\u003eThe longitudinal strain curves of the myocardial segments after coronary\u003c/p\u003e\n\u003cp\u003eartery ligation for 60 min and LDDSE. A: The absolute values of GSLsys-endo, GSLsys-mid, GSLsys-epi and SLsys-endo, SLsys-mid, and SLsys-epi in the affected segments (red, dark blue, and pink curves) decreased significantly, some above the baseline after ligation. B: After LDDSE, the survival segment curves in the affected areas (red, dark blue, and pink curves) improved significantly, all below the baseline.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4149988/v1/8d64891df728b44fe6256e62.jpg"},{"id":54360407,"identity":"3bb5d178-5293-4e7c-8e3c-195f3e6e9c69","added_by":"auto","created_at":"2024-04-09 11:00:00","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":327428,"visible":true,"origin":"","legend":"\u003cp\u003eThe longitudinal strain curves of the myocardial segments after coronary artery ligation for 90 min and LDDSE. A: The absolute values of GSLsys-endo, GSLsys-mid, GSLsys-epi and SLsys-endo, SLsys-mid, and SLsys-epi in the affected segments (red, dark blue, pink, and green curves) decreased significantly, some curves (pink and dark blue) was above the baseline after ligation. B: After LDDSE, the survival segment curves (red and some green curves) improved significantly. But in the infarcted segments (dark blue and pink curves), SLsys-endo, SLsys-mid, or SLsys-epi still decreased, partially above baseline.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4149988/v1/e7f52d7c59ec3d7fc2e23be1.jpg"},{"id":54360765,"identity":"5677bdec-7d47-45ca-aa06-718f4ba70634","added_by":"auto","created_at":"2024-04-09 11:08:01","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":322158,"visible":true,"origin":"","legend":"\u003cp\u003eThe longitudinal strain curves of the myocardial segments after coronary artery ligation for 120 min and LDDSE. A: The absolute values of GSLsys-endo, GSLsys-mid, GSLsys-epi and SLsys-endo, SLsys-mid, and SLsys-epi in the affected segments (red, dark blue, pink, and green curves) decreased significantly, almost all curves (red, dark blue, pink curves, and green partially) was above the baseline after ligation. B: After LDDSE, the survival segment curves (red, and green in SLsys-endo, SLsys-mid) improved significantly. But in the infarcted segments (pink and dark blue curves), SLsys-endo, SLsys-mid, or SLsys-epi still decreased, partially above baseline.\u003c/p\u003e","description":"","filename":"Figure5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4149988/v1/44c56840f59f0efdfcf1e2a8.jpg"},{"id":65068443,"identity":"3c5a8efd-67eb-4671-b81e-e5f15af6a67c","added_by":"auto","created_at":"2024-09-23 09:22:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3041558,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4149988/v1/1e36aabb-5e38-401c-9dd5-6a5243bdb364.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Multilayer strain and stress echocardiography can represent myocardial viability and MI model types after different ischemic durations in rabbits","fulltext":[{"header":"Background","content":"\u003cp\u003eAlthough the treatment of patients with ischemic heart disease (IHD) has made great progress in the past few decades[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], acute myocardial infarction is still associated with high morbidity and mortality[\u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. After myocardial infarction (MI), the myocardium can be divided into the necrotic and viable myocardium areas. Viable myocardium refers to the myocardium with injury after ischemia and reperfusion but still has a contractile reserve, and its damage is reversible[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. After MI, effective recovery of the blood perfusion is the key to saving the cardiac muscle[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Nevertheless, there is a possibility of recovery only if there is a viable myocardium in the affected area[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Therefore, the early evaluation of myocardial viability and functional reserve is critical for patient prognosis[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eLow-dose dobutamine stress echocardiography (LDDSE) is currently recognized as an effective technique for evaluating myocardial viability. The viable myocardium can be determined by evaluating the changes in wall motion before and after stress[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. LDDSE has a wide range of clinical applications, predictable side effects and is consistent with coronary angiography and positron emission tomography (PET) results[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Nevertheless, the assessment of abnormal wall motion is semi-quantitative and subjective, leading to a low consistency among observers[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Therefore, obtaining quantitative local myocardial deformation parameters is necessary to achieve an objective evaluation.\u003c/p\u003e \u003cp\u003eSpeckle tracking imaging (STI) is based on high frame rate two-dimensional gray-scale ultrasound images, which track the spatial motion of echogenic spots in the myocardium in real-time, without subjective influence from the examiner, without angle dependence, and with high reproducibility[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. STI can accurately evaluate left ventricular global and regional myocardial function[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. STI divides the myocardium into the endocardium, myocardium, and epicardium for functional evaluation. It can evaluate the overall and local myocardial strain function in a multi-faceted manner, understand the progress of the disease, and detect myocardial damage or improvement earlier[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The situation provides a new quantitative means for comprehensive evaluation of cardiac mechanics movement.\u003c/p\u003e \u003cp\u003eStill, the best STI parameters to predict recovery are unknown. This animal study aimed to represent myocardial viability and MI model types using multilayer strain and stress echocardiography and evaluate the sensitive STI indicators of myocardial contractile function and viability after ischemia and LDDSE. The results could provide insights into the selection of an appropriate STI indicators and animal model for future reperfusion experiments.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eAnimals\u003c/h2\u003e \u003cp\u003eThis study was carried out in strict accordance with the ARRIVE guidelines. The protocol was approved by the Committee on the animal ethics committee of the Affiliated Obstetrics and Gynecology Hospital of Tongji University. Our study is reported in accordance with ARRIVE guidelines. All possible means were taken to minimize suffering. Five-four healthy Japanese white rabbits were provided by the Animal Experimental Center of the Affiliated Obstetrics and Gynecology Hospital of Tongji University, males and females weighing 2.2\u0026ndash;3.2 kg.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eModel Establishment\u003c/h2\u003e \u003cp\u003eA multi-lead electrocardiogram (ECG) was recorded during model establishment. The rabbits were anesthetized with 3% phenobarbital sodium through the ear vein. The rabbits were kept in a natural breathing state. They were fixed on the operating table on their back. The skin was prepared. The chest was opened along the midline, and the heart was exposed layer by layer. The left atrial appendage was pinched to pull the heart. A small round needle was used to pass through the superficial myocardium about 3 mm below the left atrial appendage. A suture was used to block the left ventricular branch of the coronary artery. At the same time, a thin wire was placed in the suture for repeated ligation-reperfusion. The color of the anterior wall and apex of the left ventricle was observed to become lighter, and the pulsation weakened. The ST segment was significantly uplifted in more than two limbs or the chest lead, indicating that the left ventricular branch was successfully ligated.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eGrouping\u003c/h2\u003e \u003cp\u003eThe 54 rabbits were randomly divided into three groups (n\u0026thinsp;=\u0026thinsp;18/group): coronary artery occlusion for 60 min, coronary artery occlusion for 90 min, and coronary artery occlusion for 120 min. Each group of rabbits underwent LDDSE examination after blocking. Dobutamine was evenly pumped using a microinfusion pump at a starting dose of 5 \u0026micro;g/kg/min and increased to 10 \u0026micro;g/kg/min after 5 min. After 5 min, the drug was stopped, and the general reaction and heart rate of the rabbit were observed. Echocardiography was performed before and after coronary artery occlusion and after pumping dobutamine at 10 \u0026micro;g/kg/min. Blood (3 ml) was sampled from the rabbit ear vein and stored in a test tube.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003eTwo-dimensional echocardiography and STI\u003c/h2\u003e \u003cp\u003eA GE Vivid7 Dimension color Doppler ultrasound system with a 10s probe (frequency of 4.4\u0026ndash;11.4 MHz) (GE Healthcare, Waukesha, WI, USA) and an EchoPAC external digital ultrasound workstation equipped with STI post-processing software (GE Healthcare, Waukesha, WI, USA) were used in this study. Left ventricular end-diastolic diameter (LVDd), left ventricular end-systolic diameter (LVDs), left ventricular ejection fractions (LVEF), and heart rate were measured.\u003c/p\u003e \u003cp\u003eTwo-dimensional gray-scale dynamic images of three cardiac cycles with continuous heart rhythm stability with the long axis of the apex (four-chamber, two-chamber, three-chamber) were collected, ensuring clear intracardiac and adventome, frame rate\u0026thinsp;\u0026gt;\u0026thinsp;110 frames/s. All images were transferred into the EchoPAC external workstation. The region of interest (ROI) myocardial range was selected. The myocardial intimal curve was delineated, and the width of the ROI was adjusted. The system automatically analyzed each segment. \u0026ldquo;\u0026radic;\u0026rdquo; stood for a successful segment, while \u0026ldquo;\u0026times;\u0026rdquo; stood for an unsuccessful segment. The system accepted \u0026ldquo;\u0026radic;\u0026rdquo; segments and automatically displayed the strain and strain rate graphs for each segment. The longitudinal systolic strain (SLsys) of the left ventricle segments was recorded, including subendocardial, myocardial, and subepicardial systolic strains (SLsys-endo, SLsys-mid, and SLsys-epi, respectively) and left ventricular global longitudinal systolic strain (GSIsys), including subendocardial, myocardium, and subepicardial systolic strains (GSLsys-endo, GSLsys-mid, and GSLsys-epi, respectively).\u003c/p\u003e \u003cp\u003e \u003cb\u003eDetection of the concentration of malondialdehyde (MDA), superoxide dismutase (SOD), and tumor necrosis factor (TNF)-α in peripheral blood\u003c/b\u003e \u003c/p\u003e \u003cp\u003eRadioimmunoassay and enzyme labeling methods were used to measure MDA, SOD, and TNF-α according to the manufacturers\u0026rsquo; instructions (Bohu Institute of Biotechnology, Shanghai, China.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003eHistology\u003c/h2\u003e \u003cp\u003eAt the end of the experiment, the rabbits were sacrificed by air embolization of the ear vein. The left ventricle branch was re-ligated. Then, 10 ml of Evans blue dye was injected into the coronary artery through the aorta. After the hearts were stained blue, they were washed with physiological saline. After being frozen at -20\u0026deg;C for 15 min, the hearts were cut into 2-mm-thick sections and immersed in 2% TTC buffer at 37\u0026deg;C for 20 min. After staining, the sections were fixed in 10% formaldehyde. The myocardial infarct area, ischemic area, and left ventricular muscle area were analyzed using Image-Pro Plus 7.0 (Media Cybernetics, Inc., Rockville, MD, USA). The percentage of the infarcted myocardial area was calculated. The changes in myocardial color in each segment of the left ventricle were observed. Based on the 16-segment method recommended by the American Ultrasound Association, the viable myocardium in the necrotic zone was identified based on the staining results, and the number of segments was calculated. The infarct area was grey, the ischemic area was red, and the normal area was blue. If necrosis was observed in \u0026gt;\u0026thinsp;50% of a given segment, the segment was considered non-viable (infarcted segment)[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Otherwise, it was considered viable (ischemic segment).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAll analyses were performed using SPSS 26.0 (IBM, Armonk, NY, USA). Continuous data with normal distributions were expressed as the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD). Numerical data were tested for normal distribution using the Kolmogorov-Smirnov test. All data were analyzed using analysis of variance (ANOVA) and the LSD post hoc test. Time-point variables in echocardiographic measurements were compared using repeated measure ANOVA followed by the Student-Newman-Keuls post hoc test. P-values\u0026thinsp;\u0026lt;\u0026thinsp;0.05 were considered statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eAnimal model\u003c/h2\u003e \u003cp\u003eThere were seven (12.9%) deaths among the 54 rabbits: one deaths in the 60-min groups (mortality of 5.6%), two in 90-min groups (mortality of 11.1%) and four in 120-min group (mortality of 22.2%). After staining, the infarcted area was grayish-white, the ischemic area was brick red, and the non-ischemic area was blue (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The myocardial infarction area percentage was higher in the 120-min group (40.5%\u0026plusmn;2.8%), followed by the 90-min (29.3%\u0026plusmn;3.6%) and 60-min (16.8%\u0026plusmn;3.2%) groups (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the 60-min group, 272 segments in 17 rabbits were evaluated, including 207 (76.1%) segments of non-ischemic myocardium, 46 (16.9%) ischemic segments with viable myocardium, and 19 (7.0%) infarcted segments with non-viable myocardium. In the 90-min group, there were 189 (73.8%) non-ischemic segments, 38 (14.9%)ischemic and 29 (11.3%) infarcted segments in 256 evaluated segments of 16 rabbits. In the 120-min group, 155 (69.2%) non-ischemic segments, 35 (15.6%) ischemic and 34 (15.2%) infarcted segments in 224 segments of 14 rabbits.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eLongitudinal strain between ischemic and infarcted segments after coronary artery ligation and LDDSE\u003c/h2\u003e \u003cp\u003eAfter ligation, the absolute values of SLsys-endo, SLsys-mid, and SLsys-epi were significantly lower in the ischemic segments and infarcted segments compared with the baseline levels (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). They were not significantly different between the ischemic and infarcted segments at baseline (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). After LDDSE, the absolute values of SLsys-endo, SLsys-mid and SLsys-epi in the ischemic segments were higher than after ligation (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) in all groups. In the infarcted segments, the absolute values of SLsys-mid and SLsys-epi in 60-min group and SLsys-epi in 90-min group were higher than after ligation (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). There were no significant differences in SLsys-endo of 60-min group, SLsys-endo and SLsys-mid of 90-min group and all of 120-min group in infarcted segments after LDDSE (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLongitudinal strain between ischemic segments and infarcted segments after ligation and dobutamine stress in rabbits\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"13\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003ethe 60-min Group\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c9\" namest=\"c6\"\u003e \u003cp\u003ethe 90-min Group\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c13\" namest=\"c10\"\u003e \u003cp\u003ethe 120-min Group\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSLsys-endo (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSLsys-mid (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSLsys-epi (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSLsys-endo (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSLsys-mid (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSLsys-epi (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eSLsys-endo (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c12\"\u003e \u003cp\u003eSLsys-mid (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c13\"\u003e \u003cp\u003eSLsys-epi (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIschemic segments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-16.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-15.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-12.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-14.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-12.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-11.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e-15.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e-13.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e-12.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInfarcted segments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-15.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-14.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-12.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-15.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-13.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-11.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e-14.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e-13.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e-11.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter ligation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIschemic segments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-10.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-9.1\u0026thinsp;\u0026plusmn;\u0026thinsp;5.1\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-7.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-9.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-8.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.4\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e-8.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.0\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e-7.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e-5.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInfarcted segments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-7.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.6\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-6.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.9\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-6.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-5.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e-5.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e-4.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e-3.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter LDDSE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIschemic segments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-14.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-13.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-11.8\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-12.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-11.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-9.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e-13.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e-11.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e10.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInfarcted segments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-9.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-9.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-8.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-6.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-6.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-6.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e-5.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e-4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e-4.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"13\"\u003e\u003csup\u003ea\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. baseline within each group; \u003csup\u003eb\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. after ligation within each group; \u003csup\u003ec\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. Infarcted segments after ligation.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"13\"\u003eSLsys-endo: longitudinal systolic strain in endocardium; SLsys-mid: longitudinal systolic strain in midmyocardium; SLsys-epi: longitudinal systolic strain in the epicardium.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"13\"\u003eData are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eChanges in the left ventricular longitudinal strain at baseline and after coronary artery ligation and LDDSE in each group\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAfter coronary artery ligation, the absolute values of GSLsys-endo, GSLsys-mid, GSLsys-epi and SLsys-endo, SLsys-mid, and SLsys-epi in the affected segments were significantly lower than at baseline (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). After LDDSE, the absolute values of the above indicators in the 60-min and 90-min groups and GSLsys-endo, GSLsys-mid, GSLsys-epi in the 120-min group were significantly increased compared with those after ligation, and the differences were statistically significant (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). But, the affected segmental SLsys-endo, SLsys-mid, and SLsys-epi in the 120-min group were similar compared with those after ligation (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLeft ventricular longitudinal strain at baseline and after coronary artery ligation and dobutamine stress in rabbits\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en rabbits\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGSLsys-endo (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eGSLsys-mid (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eGSLsys-epi (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSLsys-endo (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSLsys-mid (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSLsys-epi (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e60 min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-17.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-14.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-11.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-14.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-10.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter ligation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-12.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-10.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-8.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-7.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-5.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter LDDSE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-16.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-13.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-10.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-11.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-9.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-5.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e90 min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-18.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-14.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-10.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-14.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-11.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-8.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter ligation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-8.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003csup\u003eac\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-7.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0\u003csup\u003eac\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-6.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-4.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003csup\u003eac\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-3.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003csup\u003eac\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter LDDSE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-13.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-11.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-9.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-8.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6\u003csup\u003ead\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e120 min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-18.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-13.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-10.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-15.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-12.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-8.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter ligation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-5.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9\u003csup\u003eabc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-4.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6\u003csup\u003eabc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-3.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003csup\u003eabc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003csup\u003eabc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-1.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003csup\u003eabc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003csup\u003eabc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter LDDSE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-9.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003csup\u003eabd\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-7.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003csup\u003eabd\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-6.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003csup\u003eabd\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-4.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-3.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003e\u003csup\u003ea\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. 60 min; \u003csup\u003eb\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. 90 min; \u003csup\u003ec\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. baseline within each group; \u003csup\u003ed\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. after coronary artery ligation within each group.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003eGSLsys-endo: global longitudinal systolic strain in endocardium; GSLsys-mid: global longitudinal systolic strain in midmyocardium; GSLsys-epi: global longitudinal systolic strain in epicardium; SLsys-endo: SLsys-endo: longitudinal systolic strain in endocardium; SLsys-mid: longitudinal systolic strain in midmyocardium; SLsys-epi: longitudinal systolic strain in the epicardium.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003eData are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eComparison of longitudinal strains at baseline and after coronary artery ligation and LDDSE among groups\u003c/h2\u003e \u003cp\u003eAt baseline, there were no significant differences among the three groups regarding GSLsys and local SLsys (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). After coronary artery ligation, the GSLsys-endo, GSLsys-mid, GSLsys-epi and the affected segmental SLsys-endo, SLsys-mid, SLsys-epi in the 120-min group were significantly lower than the 60-min and 90-min groups. The GSLsys-endo, GSLsys-mid and affected segmental SLsys-endo and SLsys-mid in the 90-min group were lower than the 60-min group (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Nevertheless, the differences of GSLsys-epi and affected segmental SLsys-epi between the 60-min and 90-min groups were not statistically significant (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). After LDDSE, the values of GSLsys-endo, GSLsys-mid, GSLsys-epi, SLsys-endo, SLsys-mid, and SLsys-epi in the 120-min group were significantly lower compared with the 60-min and 90-min groups (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eMDA, SOD, and TNF-α before and after coronary artery ligation and LDDSE in each group\u003c/h2\u003e \u003cp\u003eAt baseline, there were no significant differences among the three groups in MDA levels (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). After ligation and LDDSE, the differences among the three groups were statistically significant (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The MDA levels were significantly increased after ligation compared with baseline levels (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The MDA content was decreased after LDDSE in the 90-min and 120-min groups (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSerum MDA, SOD, and TNF-α at baseline and after coronary artery ligation and dobutamine stress in rabbits\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en rabbits\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMDA (nmol/ml)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSOD (U/ml)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTNF-α (pg/ml)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e60 min\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24.10\u0026thinsp;\u0026plusmn;\u0026thinsp;1.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.56\u0026thinsp;\u0026plusmn;\u0026thinsp;5.19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter ligation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.85\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.62\u0026thinsp;\u0026plusmn;\u0026thinsp;1.27\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e38.20\u0026thinsp;\u0026plusmn;\u0026thinsp;7.27\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter dobutamine stress\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e22.97\u0026thinsp;\u0026plusmn;\u0026thinsp;1.61\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e31.79\u0026thinsp;\u0026plusmn;\u0026thinsp;6.65\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e90 min\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e23.42\u0026thinsp;\u0026plusmn;\u0026thinsp;1.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21.77\u0026thinsp;\u0026plusmn;\u0026thinsp;6.81\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter ligation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.63\u003csup\u003eac\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18.74\u0026thinsp;\u0026plusmn;\u0026thinsp;1.78\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e60.54\u0026thinsp;\u0026plusmn;\u0026thinsp;8.18\u003csup\u003eac\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter dobutamine stress\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77\u003csup\u003ead\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.65\u0026thinsp;\u0026plusmn;\u0026thinsp;1.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e49.50\u0026thinsp;\u0026plusmn;\u0026thinsp;7.72\u003csup\u003ead\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e120 min\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25.13\u0026thinsp;\u0026plusmn;\u0026thinsp;1.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.57\u0026thinsp;\u0026plusmn;\u0026thinsp;6.69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter ligation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.72\u003csup\u003eabc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.17\u0026thinsp;\u0026plusmn;\u0026thinsp;1.75\u003csup\u003eabc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e74.47\u0026thinsp;\u0026plusmn;\u0026thinsp;7.53\u003csup\u003eabc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter dobutamine stress\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.60\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83\u003csup\u003eabd\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18.23\u0026thinsp;\u0026plusmn;\u0026thinsp;1.88\u003csup\u003ead\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e60.60\u0026thinsp;\u0026plusmn;\u0026thinsp;7.94\u003csup\u003eabd\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003ea\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. 60 min; \u003csup\u003eb\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. 90 min; \u003csup\u003ec\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. baseline within each group; \u003csup\u003ed\u003c/sup\u003e P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 vs. after coronary artery ligation within each group.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eMDA: malondialdehyde; SOD: superoxide dismutase; TNF-α: tumor necrosis factor-α.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eData are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAt baseline, there were no significant differences among the three groups in SOD levels (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). After ligation, the differences between the 60-min and 120-min groups were statistically significant (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), and the content of SOD was decreased. Compared with after ligation, SOD levels in the 120-min group increased after LDDSE (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAt baseline, there were no significant differences among the three groups in TNF-α levels (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). After ligation and LDDSE, the difference among the three groups were significantly different (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), significantly increased after ligation (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), and decreased after LDDSE compared with after ligation (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe viable myocardium is the myocardium with reversible myocardial injury and contractile reserve. In most previous studies, viable myocardium was assessed by establishing a myocardial ischemia-reperfusion model, often overlooking the presence of viable myocardium after coronary ischemia. After reperfusion, there is no reliable basis for the recovery of some myocardial function. This study aimed to represent myocardial viability and evaluate the reliable and sensitive multilayer strain and stress echocardiography indicators of myocardial contractile function and viability after ischemia and LDDSE. The results suggest that layer-specific strain of STI combined with LDDSE can accurately evaluate the changes in myocardial systolic function and viability in rabbits with different ischemic durations. These could provide insights into the selection of an appropriate STI indicators for future reperfusion experiments. These results are supported by Ben DA et al.[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMyocardial viability is different according to ischemic time[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e21\u003c/span\u003e], but there are few studies on myocardial viability and myocardial function reserve after different ischemic times. Studies showed that ischemia could lead to coronary microvascular dysfunction, and the degree of damage is affected by the duration of ischemia[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The ischemic myocardium has more lactic acid production, which increases with the increase of ischemia time. In this study, the number of viable myocardium segments decreased with increasing blocking time. The GSLsys-endo, GSLsys-mid, GSLsys-epi, and blocking segments of SLsys-endo, SLsys-mid, and SLsys-epi in the 120-min group with fewer viable myocardium segments were significantly lower than in the 60-min and 90-min groups, suggesting that different blocking times may have different effects on the mechanical function of the viable myocardium.\u003c/p\u003e \u003cp\u003eIn recent years, with the deepening of research on the mechanism of cardiovascular disease, some studies have found that oxidative stress is closely related to the occurrence and development of various cardiovascular diseases, which may be one of the common mechanisms of cardiovascular disease and play a certain role in the course of atherosclerosis[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. SOD is one of the oxygen free radical scavengers in the body, reducing the damage of oxygen free radicals on cells[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Its activity can be used to assess the degree of oxygen free radical scavenging ability. MDA is a product of lipid peroxidation, and its amount can reflect the degree of oxidative stress in the body[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. In this study, with the increase of coronary artery occlusion time, the activity of SOD decreased, and the activity of MDA increased, indicating that the ability of cardiomyocytes to scavenge oxygen free radicals decreased and the oxidative stress response increased with the increase of ischemia time, also reflecting the degree of ischemia and hypoxia in cells[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn addition, studies showed that active inflammatory reaction in atherosclerotic plaques might be another important risk factor for the increasing severity of coronary heart disease[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. TNF-α is an important inflammatory cytokine and plays an important role in inducing local adhesion, aggregation, activation, and damage of inflammatory cells. In this study, with the increase of coronary artery occlusion time, the TNF-α content of rabbits in each group increased significantly. This phenomenon might be caused by an increase in reactive oxygen species due to the action of inflammatory cytokines after acute myocardial infarction. In turn, the increase in reactive oxygen species increases myocardial damage, which leads to a vicious circle that further aggravates myocardial damage over time.\u003c/p\u003e \u003cp\u003eSzymczyk et al. [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e30\u003c/span\u003e]considered that the absolute value of the longitudinal strain has a higher prediction probability for the corresponding contraction reserve of the viable myocardium, and the larger the absolute value of the longitudinal strain may correspond to a better reserve function. In this study, the absolute value of GSLsys in each layer of the left ventricle and SLsys-endo, SLsys-mid, and SLsys-epi of the viable myocardium after LDDSE were increased in all groups. However, in the infarcted segments, the absolute values of SLsys-mid and SLsys-epi in 60-min group and SLsys-epi in 90-min group were higher than after ligation. And there were no significant differences in SLsys-endo of 60-min group, SLsys-endo and SLsys-mid of 90-min group and all of 120-min group in infarcted segments after LDDSE. These indicated that it was transmural myocardial infarction in the 120-min group and subendocardial myocardial infarction in the 60-min group. And this was also confirmed by histopathological findings. The GSLsys and the affected segmental SLsys in the 120-min group were significantly lower than in the other two groups after ligation and LDDSE. The probability of ventricular fibrillation in rabbits increased significantly during the experiment, and mortality increased consequently. Therefore, after comprehensive consideration, we may prefer to use the 90-min coronary artery occlusion model as the next acute infarction reperfusion animal model. So the multilayer strain and stress echocardiography may represent myocardial viability in different layers and MI model types in rabbits. The results could help in the selection of an appropriate animal model for future reperfusion experiments.\u003c/p\u003e \u003cp\u003eIn the present study, the viability and functional reserve of myocardium after different ischemic durations by multilayer strain and stress echocardiography, which can reflect the changes of whole and local myocardial function and myocardial cell damage before and after coronary artery occlusion. This technique is non-invasive, objective, and not affected by the operator, which is more suitable for clinical use[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The changes of SLsys-endo under the endometrium were the most pronounced and consistent with pathological findings. So SLsys-endo could refer as the indicator to early detect the subendocardial myocardial ischemia and infarction.\u003c/p\u003e \u003cp\u003eThis study has limitations. First, the number of animals included in this study was limited. The results of this study should be confirmed by a larger sample size study. STI stratified strain requires a high frame rate and clear display of the ventricular endocardium, myocardium, and epicardium, which requires high image quality, but some images were unclear due to the rapid heart rate of rabbits. Rabbit anatomy and coronary angiography are similar to humans, but there are still differences.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn conclusion, with the increase of coronary artery occlusion time, the infarcted myocardium increased, and the myocardial viability, the functional reserve of viable myocardium, and the systolic function decreased. Combined with LDDSE, STI can accurately assess myocardial viability and contractile reserve changes at different ischemic times. This study could provide insights into the selection of an appropriate STI indicators and animal model for future reperfusion experiments.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYHY and DLP contributed equally to the article. YHY and DLP were responsible for the substantial contributions to the conception, design of the work and drafted the work, JZH analysised and interpreted the data, LKT contributed to the conception of the manuscript, RM and LYJ were responsible for the modification of language. DLP was responsible for substantial contributions to the conception, revision of the work, and ensure that all listed authors have approved the manuscript before submission.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSome of the data that support the findings of this study are available from the Second Affiliated Hospital of Harbin Medical University but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. If someone wants to request the data from our study, data are available from the Min Ren（[email protected]）upon reasonable request and with permission of the Second Affiliated Hospital of Harbin Medical University.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was approved by the animal ethics committee of the Affiliated Obstetrics and Gynecology Hospital of Tongji University（TJBG03324201）.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor details\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eDepartment of Ultrasound Medicine, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai 200092, China.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e2\u003c/sup\u003eDepartment of Ultrasound Medicine, The Sixth People\u0026apos;s Hospital Affiliated to Shanghai Jiao Tong University, Shanghai 201306, China.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e3\u003c/sup\u003eDepartment of Ultrasound Medicine, The Second Affiliated Hospital of Harbin Medical University, Harbin 150086, China.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e4\u003c/sup\u003eDepartment of Ultrasound Medicine, Sanya Central Hospital (Hainan Third People\u0026rsquo;s Hospital), Sanya 572000, China.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eVirani SS, Newby LK, 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\u003cstrong\u003e17\u003c/strong\u003e(5):374-381.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"speckle tracing imaging, myocardial ischemia, viable myocardium, dobutamine stress","lastPublishedDoi":"10.21203/rs.3.rs-4149988/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4149988/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eTo investigate myocardial viability and MI model types using multilayer strain and stress echocardiography and evaluate the sensitive STI indicators of myocardial contractile function and viability.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eFifty-four rabbits were randomly divided into the 60-min, 90-min, and 120-min coronary artery occlusion groups. Blood collections and speckle tracking echocardiography (STE) were performed at baseline, after ligation, and after low-dose dobutamine stress echocardiography (LDDSE). The ratio of infarcted myocardium to viable myocardium was calculated using Evans Blue-TTC.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eAfter ligation, the ventricular global endocardial longitudinal strain (GSLsys-endo), global myocardial longitudinal strain (GSLsys-mid), and global epicardial longitudinal strain (GSLsys-epi) decreased in the three groups (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05); longitudinal strain of endocardium (SLsys-endo), longitudinal strain of myocardium (SLsys-mid), and longitudinal strain of epicardium (SLsys-epi) decreased in the affected segments (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). After LDDSE, the absolute values of the above indicators in the 60-min and 90-min groups and GSLsys-endo, GSLsys-mid, GSLsys-epi in the 120-min group were significantly increased (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The absolute values of SLsys-endo, SLsys-mid and SLsys-epi in the ischemic segments increased (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) in all groups. In the infarcted segments, the absolute values of SLsys-mid and SLsys-epi in 60-min group, SLsys-epi in 90-min group and none in 120-min group increased (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). After coronary artery occlusion, malondialdehyde and tumor necrosis factor-α levels were increased, and superoxide dismutase was decreased (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The myocardial infarction area percentage was higher in the 120-min group (40.5%\u0026plusmn;2.8%), followed by the 90-min (29.3%\u0026plusmn;3.6%) and 60-min (16.8%\u0026plusmn;3.2%) groups (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The mortality of the 120-min group was higher than in the two other groups (22.2% vs. 5.6% and 11.1%, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eMultilayer strain and stress echocardiography can evaluate myocardial viability and MI model types in rabbits after different ischemic durations and provide insights into the selection of an appropriate STI indicators and animal model for future reperfusion experiments.\u003c/p\u003e","manuscriptTitle":"Multilayer strain and stress echocardiography can represent myocardial viability and MI model types after different ischemic durations in rabbits","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-09 10:59:55","doi":"10.21203/rs.3.rs-4149988/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a29d70cc-ad8b-4677-889f-817fb9db5350","owner":[],"postedDate":"April 9th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-09-23T09:14:43+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-09 10:59:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4149988","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4149988","identity":"rs-4149988","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}