Electromechanical Window as an Integrative Marker of Remodeling and Arrhythmic Risk in Biventricular vs Left Bundle Branch Area Pacing

Electromechanical Window as an Integrative Marker of Remodeling and Arrhythmic Risk in Biventricular vs Left Bundle Branch Area Pacing | 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 Electromechanical Window as an Integrative Marker of Remodeling and Arrhythmic Risk in Biventricular vs Left Bundle Branch Area Pacing Arvind Kumar, Tania Bansal, Salil Jaura This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9503125/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Background The electromechanical window (EMW), defined as difference between mechanical and electrical systole, is an emerging marker of arrhythmic risk and ventricular dysfunction. Although cardiac resynchronization therapy (CRT) improves mechanical synchrony, the influence of different pacing strategies on EMW is not well established. Left bundle branch area pacing (LBBAP) provides more physiological ventricular activation than biventricular (BiV) pacing. This study compared the effects of BiV pacing and LBBAP on EMW and examined its association with CRT response and arrhythmic burden. Methods In this prospective study, 80 patients with LVEF ≤ 35% undergoing CRT were assigned to BiV pacing (n = 40) or LBBAP (n = 40). Echocardiography with simultaneous ECG was performed at baseline and 6 months. EMW was calculated as the interval from QRS onset to aortic valve closure minus the QT interval. Secondary measures included QRS duration, global longitudinal strain (GLS), left ventricular end-systolic volume (LVESV), and LVEF. CRT response was defined as ≥ 15% reduction in LVESV. Results LBBAP achieved greater QRS narrowing and larger EMW improvement than BiV pacing. EMW improvement correlated with LVESV reduction (r = 0.46, p < 0.001) and GLS improvement (r = 0.42, p = 0.002). CRT response was more frequent with LBBAP (70% vs 50%, p = 0.048). Baseline EMW predicted CRT response (AUC 0.71; cutoff − 35 ms: 68% sensitivity, 70% specificity). Persistent EMW negativity was associated with higher non-sustained ventricular tachycardia incidence (45% vs 18%, p = 0.01). Conclusion LBBAP provides greater EMW normalization and reverse remodeling than BiV pacing. EMW correlates with structural recovery and may serve as a physiological marker of CRT response and arrhythmic vulnerability. Electromechanical window Cardiac resynchronization therapy Left bundle branch area pacing Ventricular remodelling Arrhythmia Figures Figure 1 Figure 2 Introduction Cardiac resynchronization therapy (CRT) is an established treatment for patients with heart failure with reduced ejection fraction (HFrEF), electrical dyssynchrony, and persistent symptoms despite optimal medical therapy. Conventional CRT using biventricular (BiV) pacing improves ventricular synchrony, promotes reverse remodeling, and reduces morbidity and mortality; however, up to one-third of patients remain non-responders, underscoring the need for more physiological pacing strategies and improved markers of electromechanical recovery.¹⁻³ Left bundle branch area pacing (LBBAP) has emerged as a form of conduction system pacing capable of achieving near-normal ventricular activation through engagement of the His–Purkinje system. Compared with conventional BiV pacing, LBBAP produces narrower QRS complexes and may result in superior mechanical synchrony and ventricular remodeling. Early observational studies and multicenter registries suggest that LBBAP-based CRT may offer improved electrical resynchronization and favorable echocardiographic response.⁴⁻⁷ While electrical resynchronization is commonly assessed using QRS duration, this parameter does not fully capture the complex interplay between myocardial depolarization, repolarization, and mechanical contraction. The electromechanical window (EMW), defined as the difference between mechanical systole and electrical systole, has emerged as a noninvasive marker of electromechanical coupling. A negative EMW reflects delayed mechanical contraction relative to repolarization and has been associated with arrhythmic risk and myocardial dysfunction.⁸⁻¹¹ CRT has the potential to improve EMW by restoring coordinated ventricular contraction, yet the comparative effects of different pacing modalities on EMW remain poorly studied. Understanding whether physiologic pacing strategies such as LBBAP provide superior normalization of EMW may offer mechanistic insight into differences in remodeling and possibly arrhythmic risk. Therefore, this study compared the impact of BiV pacing and LBBAP on EMW and evaluated the relationship between EMW changes, CRT response, reverse ventricular remodeling, and arrhythmic burden. Methods This prospective, single-center observational study enrolled 80 consecutive patients with HFrEF who underwent device implantation for CRT between January 2023 and June 2025. Eligible patients had left ventricular ejection fraction (LVEF) of 35% or less, New York Heart Association functional class II–IV symptoms despite guideline-directed medical therapy, and a QRS duration ≥ 130 ms with left bundle branch block morphology or ≥ 150 ms with non–left bundle branch block morphology. Exclusion criteria included permanent atrial fibrillation with uncontrolled ventricular rates, significant primary valvular disease requiring surgical intervention, prior CRT implantation, and inadequate echocardiographic imaging windows. Patients underwent either conventional biventricular (BiV) pacing or left bundle branch area pacing (LBBAP) according to operator expertise and anatomical feasibility. BiV pacing was performed using standard right atrial, right ventricular, and coronary sinus left ventricular leads. LBBAP was achieved via transseptal lead deployment targeting the left bundle branch area. Conduction system capture was confirmed using standard electrocardiographic criteria, including right bundle branch block–like morphology and short stimulus-to–left ventricular activation time. Transthoracic echocardiography with simultaneous electrocardiographic recording was performed at baseline and six months after implantation using a standardized acquisition protocol. Left ventricular volumes and ejection fraction were calculated using the Simpson biplane method, and global longitudinal strain (GLS) was assessed using speckle-tracking echocardiography. Mechanical systole was defined as the interval from QRS onset to aortic valve closure (AoC) measured using continuous-wave Doppler in the left ventricular outflow tract. Electrical systole was defined as the QT interval from QRS onset to the end of the T wave on the simultaneously recorded electrocardiogram. EMW was calculated as mechanical systole minus the QT interval (EMW = QAoC – QT, Fig. 1 ), with negative values indicating electromechanical uncoupling. All EMW measurements were averaged over three consecutive cardiac cycles to improve measurement accuracy and reduce beat-to-beat variability. The primary endpoint was the change in EMW at six months. Secondary endpoints included changes in QRS duration, GLS, left ventricular end-systolic volume (LVESV), and CRT response, defined as a ≥ 15% reduction in LVESV at follow-up. Device interrogation at six months was used to assess atrial and ventricular arrhythmic events. Statistical Analysis Statistical analyses were performed using standard statistical software. Continuous variables are presented as mean ± standard deviation and categorical variables as counts and percentages. Within-group changes from baseline to six months were assessed using paired t-tests or Wilcoxon signed-rank tests as appropriate. Between-group comparisons (BiV vs LBBAP) were performed using independent t-tests or Mann–Whitney U tests. Categorical variables were compared using the chi-square or Fisher’s exact test. Correlations between changes in EMW and echocardiographic parameters were evaluated using Pearson or Spearman correlation coefficients. Multivariable linear regression analysis was performed to identify independent predictors of EMW improvement. Receiver operating characteristic (ROC) analysis was used to assess the ability of baseline EMW to predict CRT response. A two-tailed p value < 0.05 was considered statistically significant. Results Baseline demographic, clinical, and echocardiographic characteristics were comparable between groups. The mean age of the study population was 62 ± 10 years, and 72% were male. Baseline mean LVEF was 27.5 ± 5.5%, mean LVESV was 155 ± 35 mL, QRS duration was 163 ± 19 ms, and electromechanical window (EMW) was − 37 ± 21 ms. Both pacing groups had similar baseline parameters (Table 1 ). Table 1 Baseline Characteristics Parameter All Patients (n = 80) BiV Pacing (n = 40) LBBAP (n = 40) p value (BiV vs LBBAP) Age (years) 62 ± 10 63 ± 9 61 ± 11 0.38 Male sex (%) 72% 70% 75% 0.62 LVEF (%) 27.5 ± 5.5 28 ± 5 27 ± 6 0.42 LVESV (mL) 155 ± 35 158 ± 36 152 ± 34 0.42 QRS (ms) 163 ± 19 162 ± 18 165 ± 20 0.48 EMW (ms) −37 ± 21 −36 ± 20 −38 ± 22 0.67 In the LBBAP group, successful conduction system capture at implantation was achieved in 36 of 40 patients (90%) and at six-month follow-up, it was maintained in 34 of 40 patients (85%), with loss of capture in 2 patients and transition to myocardial septal pacing in 4 patients. In the BiV pacing group, left ventricular lead placement in lateral or posterolateral coronary sinus branches was achieved in 32 of 40 patients (80%), while the remaining patients had leads positioned in anterolateral or mid-cardiac veins due to anatomical constraints. At six months, both pacing strategies resulted in significant QRS narrowing; however, the reduction was greater with LBBAP (42 ± 15 ms vs 28 ± 13 ms, p < 0.001). EMW improved significantly in both groups, with a greater degree of normalization in the LBBAP group (from − 38 ± 22 ms to − 5 ± 18 ms) compared with the BiV group (from − 36 ± 20 ms to − 18 ± 19 ms; between-group p = 0.003). Improvements in LVEF, GLS, and LVESV were observed in both groups but were more pronounced with LBBAP (Table 2 ). Table 2 Six-Month Electrical, Echocardiographic, and Clinical Outcomes Parameter Time Point All Patients (n = 80) BiV Pacing (n = 40) LBBAP (n = 40) p value (BiV vs LBBAP) QRS (ms) 6 months 128 ± 17 134 ± 16 123 ± 14 < 0.001 Change −35 ± 16 −28 ± 13 −42 ± 15 < 0.001 EMW (ms) 6 months −12 ± 19 −18 ± 19 −5 ± 18 0.004 Change + 26 ± 18 + 18 ± 16 + 33 ± 17 0.003 LVEF (%) 6 months 36.5 ± 7 35 ± 6 38 ± 7 0.02 Change + 9 ± 6 + 7 ± 5 + 11 ± 6 0.004 GLS (%) 6 months −14.9 ± 3.1 −13.6 ± 2.9 −16.3 ± 3.0 0.001 Change −5.1 ± 2.4 −4.1 ± 2.3 −6.2 ± 2.1 0.001 LVESV (mL) 6 months 125 ± 32 134 ± 34 116 ± 28 0.01 Change (%) −19 ± 11 −15 ± 10 −22 ± 11 0.01 CRT Response (%) 6 months 60% 50% 70% 0.048 HARE 6 months 31% 40% 22% 0.048 NSVT 6 months 25% 35% 15% 0.03 Improvement in EMW correlated with LVESV reduction (r = 0.46, p < 0.001), GLS improvement (r = 0.42, p = 0.002), LVEF improvement (r = 0.39, p = 0.004), and QRS narrowing (r = 0.35, p = 0.01), supporting its association with both electrical and mechanical recovery (Table 3 ). Table 3 Correlation of Change in EMW with Echocardiographic and Electrical Parameters Parameter Correlation Coefficient (r) p value LVESV reduction (%) 0.46 < 0.001 LVEF improvement (%) 0.39 0.004 Global longitudinal strain improvement 0.42 0.002 QRS narrowing (ms) 0.35 0.01 Final EMW at 6 months (ms) 0.58 < 0.001 Multivariable linear regression analysis identified independent predictors of EMW improvement at six months. Greater LVESV reduction (β = 0.34, p = 0.001), GLS improvement (β = 0.29, p = 0.003), and use of LBBAP rather than BiV pacing (β = 0.31, p = 0.002) were independently associated with greater EMW normalization. Baseline EMW also independently predicted EMW change (β=−0.22, p = 0.01), while QRS narrowing showed a weaker but significant association (β = 0.18, p = 0.02). The overall model explained 48% of the variance in EMW improvement (R²=0.48, p < 0.001) (Table 4 ). Table 4 Multivariable Linear Regression Analysis for Predictors of EMW Improvement Variable Standardized β Coefficient Standard Error p value LVESV reduction (%) 0.34 0.09 0.001 GLS improvement 0.29 0.08 0.003 LBBAP vs BiV pacing 0.31 0.10 0.002 Baseline EMW (ms) −0.22 0.08 0.01 QRS narrowing (ms) 0.18 0.07 0.02 Device interrogation at six months revealed a higher arrhythmic burden in the BiV group (Table 2 ). High atrial rate episodes (HARE) occurred in 40% of BiV patients compared with 22% in the LBBAP group (p = 0.048), and non-sustained ventricular tachycardia (NSVT) was observed in 35% versus 15%, respectively (p = 0.03). Persistent EMW negativity at follow-up was associated with a higher incidence of NSVT, irrespective of pacing modality (45% in patients with persistent EMW negativity vs 18% in those with EMW normalization, p = 0.01). CRT response, defined as a ≥ 15% reduction in LVESV, occurred more frequently in the LBBAP group than in the BiV group (70% vs 50%, p = 0.048). Baseline EMW was significantly more negative in responders than in non-responders (− 42 ± 21 ms vs − 29 ± 18 ms, p = 0.01). Responders demonstrated greater EMW normalization at follow-up (+ 34 ± 18 ms vs + 16 ± 14 ms, p = 0.002) and less residual EMW negativity (− 8 ± 17 ms vs − 19 ± 20 ms, p = 0.01) (Table 5 ). Receiver operating characteristic analysis showed that baseline EMW predicted CRT response with moderate accuracy (AUC 0.71) (Fig. 2 ); a cutoff value of − 35 ms provided 68% sensitivity and 70% specificity. Table 5 Baseline and Follow-Up Characteristics of CRT Responders vs Non-Responders Parameter CRT Responders (n = 48) Non-Responders (n = 32) p value Age (years) 61 ± 9 63 ± 11 0.34 Male sex (%) 73% 69% 0.68 Baseline LVEF (%) 27 ± 5 28 ± 6 0.37 Baseline LVESV (mL) 160 ± 34 148 ± 36 0.09 Baseline QRS (ms) 166 ± 19 159 ± 17 0.07 Baseline EMW (ms) −42 ± 21 −29 ± 18 0.01 EMW change at 6 months (ms) + 34 ± 18 + 16 ± 14 0.002 Final EMW (ms) −8 ± 17 −19 ± 20 0.01 LVEF improvement (%) + 13 ± 6 + 4 ± 3 < 0.001 LVESV reduction (%) −28 ± 8 −6 ± 5 < 0.001 GLS improvement −7.2 ± 2.1 −2.4 ± 1.6 < 0.001 NSVT at 6 months (%) 17% 38% 0.03 Structural and functional recovery were also more pronounced among responders, with larger improvements in LVEF (+ 13 ± 6% vs + 4 ± 3%, p < 0.001), greater LVESV reduction (− 28 ± 8% vs − 6 ± 5%, p < 0.001), and greater improvement in global longitudinal strain (− 7.2 ± 2.1 vs − 2.4 ± 1.6, p < 0.001). Non-responders exhibited a higher incidence of NSVT at follow-up (38% vs 17%, p = 0.03), while baseline demographic and clinical characteristics were otherwise similar between groups (Table 5 ). Discussion This study demonstrates that both conventional BiV pacing and LBBAP improve electromechanical coupling, as reflected by a shift of EMW toward less negative values. However, LBBAP produced significantly greater EMW normalization, more pronounced reverse remodeling, and superior electrical resynchronization at six months. These findings extend growing evidence that conduction system pacing restores more physiological ventricular activation than conventional epicardial left ventricular stimulation.⁴⁻⁷ Importantly, our results indicate that the advantages of LBBAP extend beyond QRS narrowing to more complete restoration of global electromechanical timing. The electromechanical window integrates electrical repolarization and mechanical systole into a single parameter, thereby reflecting overall electromechanical interaction rather than isolated electrical or mechanical phenomena. A negative EMW has been associated with arrhythmic risk in long QT syndrome, cardiomyopathies, and acquired repolarization disorders.⁸⁻¹¹ In the context of CRT, EMW improvement likely represents better temporal alignment between depolarization, repolarization, and myocardial contraction. The greater EMW normalization observed with LBBAP suggests that activation through the native His–Purkinje system more effectively restores this delicate electromechanical balance. Consistent with prior studies, LBBAP achieved greater QRS narrowing and more favorable improvements in LVEF, LVESV, and GLS compared with BiV pacing.⁵⁻⁷,¹² While earlier investigations primarily emphasized electrical and volumetric outcomes, our study adds mechanistic insight by demonstrating that EMW improvement parallels structural and functional recovery. Correlation analysis showed that EMW normalization was associated with LVESV reduction, GLS improvement, LVEF improvement, and QRS narrowing, supporting the concept that EMW reflects integrated electromechanical recovery rather than electrical resynchronization alone. Multivariable analysis further strengthened this interpretation, demonstrating that EMW improvement was independently associated with reverse remodeling, myocardial strain recovery, and pacing modality. Importantly, LBBAP remained an independent determinant of EMW normalization even after adjustment for changes in QRS duration and ventricular function, suggesting that conduction system pacing confers intrinsic electromechanical advantages beyond simple electrical shortening. Our study also highlights the predictive role of EMW. Patients with more negative baseline EMW values were more likely to exhibit CRT response, and baseline EMW demonstrated moderate discriminative ability for predicting reverse remodeling. Responders showed greater EMW normalization and less residual EMW negativity at follow-up, along with larger improvements in LVEF, LVESV, and GLS. These findings suggest that EMW may serve not only as a marker of treatment effect but also as a potential tool for identifying patients most likely to benefit from CRT. Importantly, electromechanical recovery appeared closely linked to arrhythmic risk. Device interrogation revealed a higher burden of atrial and ventricular arrhythmias in the BiV group, paralleling the lesser degree of EMW normalization observed in these patients. Moreover, persistent EMW negativity at six months was associated with a significantly higher incidence of non-sustained ventricular tachycardia compared with EMW normalization (45% vs 18%), irrespective of pacing modality. Similarly, CRT non-responders—who exhibited less EMW improvement and greater residual EMW negativity—had a higher burden of NSVT. These findings support the concept that incomplete restoration of electromechanical synchrony reflects ongoing dispersion of repolarization and mechanical dyssynchrony, creating a substrate vulnerable to ventricular arrhythmias. From a clinical perspective, EMW may represent a novel integrative biomarker linking electrical resynchronization, mechanical recovery, and arrhythmic vulnerability. Traditional CRT assessment relies heavily on QRS duration and volumetric response, which do not consistently capture arrhythmic risk or electromechanical stability. EMW offers a noninvasive measure that bridges electrical and mechanical domains and may provide incremental value for comparing pacing strategies, identifying CRT responders, and recognizing patients at continued arrhythmic risk despite therapy.¹³,¹⁴ Although our study was not powered for definitive clinical arrhythmic endpoints, the consistent association between EMW normalization, reverse remodeling, and reduced ventricular arrhythmia burden raises the hypothesis that conduction system pacing may confer anti-arrhythmic benefit by restoring electromechanical synchrony more effectively than conventional BiV pacing. This mechanistic link warrants validation in larger prospective studies with long-term adjudicated arrhythmic and survival outcomes. Conclusion In patients with heart failure undergoing cardiac resynchronization therapy, left bundle branch area pacing resulted in greater normalization of the electromechanical window and superior reverse ventricular remodeling compared with conventional biventricular pacing. Improvement in EMW correlated with reductions in LV end-systolic volume and improvements in myocardial strain, supporting its role as an integrative marker of electromechanical recovery rather than electrical resynchronization alone. Baseline EMW negativity predicted CRT response, and persistent EMW abnormalities were associated with a higher burden of device-detected ventricular arrhythmias, suggesting that EMW may also reflect residual arrhythmic substrate. These findings highlight the electromechanical window as a promising noninvasive physiological marker that links electrical activation, mechanical recovery, and arrhythmic vulnerability. Incorporation of EMW assessment into CRT evaluation may improve patient selection, aid comparison of pacing strategies, and help identify individuals at continued arrhythmic risk despite therapy. Larger multicenter studies with long-term clinical outcomes are warranted to validate EMW-guided approaches in cardiac resynchronization therapy. Limitations and Further Considerations Single-center, nonrandomized design with potential selection bias Modest sample size not powered for hard clinical outcomes Short follow-up duration (6 months) Lack of standardized device optimization protocols across patients EMW measurement not yet widely standardized; possible interobserver variability No assessment of long-term arrhythmic events or ICD therapies Absence of advanced imaging (e.g., CMR) to evaluate scar and fibrosis Findings require validation in multicenter randomized trials Future studies should assess whether EMW-guided CRT optimization improves outcomes Abbreviations • BiV Biventricular • CRT Cardiac Resynchronization Therapy • EMW Electromechanical Window • GLS Global Longitudinal Strain • HARE High Atrial Rate Episodes • HFrEF Heart Failure with Reduced Ejection Fraction • LBBAP Left Bundle Branch Area Pacing • LV Left Ventricle / Left Ventricular • LVEF Left Ventricular Ejection Fraction • LVESV Left Ventricular End–Systolic Volume • NSVT Non–Sustained Ventricular Tachycardia • NYHA New York Heart Association • QRS QRS Complex • ROC Receiver Operating Characteristic Declarations Declaration of generative AI and AI-assisted technologies in the manuscript preparation process During the preparation of this work the author(s) used ChatGPT in order to paraphrase few sentences. After using this tool/service, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the published article. Ethics declarations Ethics approval and consent to participate The study was carried out in accordance with the principles of the Declaration of Helsinki and was approved by Pragma Medical Institute’s Institutional Ethics Committee (IEC/2024/004). Written informed consent was taken for each participant. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Author Contribution A.K. wrote the main manuscript text and T.B. and S.J. helped in data collection and analysis. All authors reviewed the manuscript. References McDonagh TA et al (2021) 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. Eur Heart J Writing Committee Members (2022) 2022 AHA/ACC/HFSA Guideline for the Management of Heart Failure. Circulation Cleland JGF et al (2005) The effect of cardiac resynchronization on morbidity and mortality in heart failure. N Engl J Med Huang W et al (2020) Left bundle branch pacing: current knowledge and future prospects. JACC Clin Electrophysiol Jastrzębski M et al (2022) Left bundle branch area pacing outcomes: results from the MELOS registry. Eur Heart J Vijayaraman P et al (2021) Conduction system pacing. J Am Coll Cardiol Wu S et al (2023) Left bundle branch pacing vs biventricular pacing for CRT: a multicenter comparison. Heart Rhythm Ter Bekke RMA, Volders PGA (2020) The electromechanical window: a novel marker of arrhythmic risk. Heart Rhythm Odening KE et al (2021) Electromechanical reciprocity and arrhythmogenesis. Eur Heart J Deissler PM, Volders PGA, Ter Bekke RMA (2025) The electromechanical window for arrhythmia-risk assessment. Heart Rhythm 22(1):118–127. 10.1016/j.hrthm.2024.06.012 Epub 2024 Jun 13. PMID: 38878938 Rhee TM et al (2023) Predictive value of electromechanical window for ventricular arrhythmia. J Korean Med Sci Sharma PS et al (2022) Permanent His bundle pacing and LBB pacing for CRT. JACC Clin Electrophysiol Mafi-Rad M et al (2016) Mechanical dyssynchrony and CRT response. Europace Upadhyay GA et al (2015) On-treatment QRS narrowing and CRT outcomes. Circulation Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 24 Apr, 2026 Editor assigned by journal 23 Apr, 2026 Submission checks completed at journal 23 Apr, 2026 First submitted to journal 23 Apr, 2026 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. 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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-9503125","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":634069222,"identity":"51ba54ae-4e78-4537-85dd-3d184d4b09e9","order_by":0,"name":"Arvind Kumar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABBElEQVRIiWNgGAWjYBACAzBZcICBjYEHyKgAYmbmBiK0GIC1MDYwnAFpYSRSCwNIC2MbiEdAizn72cMffhjckePjX3v84c95tdH87UAtPyq24dRi2ZOXJtlj8MyYTeJdYjPvtuO5Mw4Dbes5cxu3ww7kmDHwGBxObJM4Y9jMuO1YbgNQCzNjGx4t598Yf/xjcLgepKXx55xjufMJarmRYyANtCWBjb/HsIG3oSZ3AyEtljPemEnLGBw2bJPgMZzNc+xA7kagloP4/GLOn2P88U3FYXn5/jMGH3/U1OXOO3/44IMfFbi1IIBEAog8DGYfIEI9EPCD1dURp3gUjIJRMApGFAAAUoRf1od5qroAAAAASUVORK5CYII=","orcid":"","institution":"Pragma Medical Institute","correspondingAuthor":true,"prefix":"","firstName":"Arvind","middleName":"","lastName":"Kumar","suffix":""},{"id":634069223,"identity":"7157f9fd-8e2a-45a0-92ad-adc3816a0629","order_by":1,"name":"Tania Bansal","email":"","orcid":"","institution":"Adesh Institute of Medical Sciences \u0026 Research","correspondingAuthor":false,"prefix":"","firstName":"Tania","middleName":"","lastName":"Bansal","suffix":""},{"id":634069224,"identity":"1b500570-839d-4ae3-b275-3d1dbc80861c","order_by":2,"name":"Salil Jaura","email":"","orcid":"","institution":"Pragma Medical Institute","correspondingAuthor":false,"prefix":"","firstName":"Salil","middleName":"","lastName":"Jaura","suffix":""}],"badges":[],"createdAt":"2026-04-23 06:54:03","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9503125/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9503125/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108821345,"identity":"5eeb7bed-c4ca-473a-87fc-633ba60b1722","added_by":"auto","created_at":"2026-05-08 16:45:28","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":128197,"visible":true,"origin":"","legend":"\u003cp\u003eApical 5-chamber view demonstrating measurement of the electromechanical window (EMW). Mechanical systole (QAoC) was defined as the interval from QRS onset to aortic valve closure (AoC), obtained from continuous-wave Doppler of the left ventricular outflow tract. Electrical systole was defined as the QT interval measured from QRS onset to the end of the T wave on the simultaneously recorded electrocardiogram. EMW was calculated as QAoC minus the QT interval, with negative values indicating electromechanical uncoupling.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9503125/v1/fa68f4790dfac52de765857d.jpeg"},{"id":108821438,"identity":"e37ab53d-9135-4fe7-972a-18993e513f1f","added_by":"auto","created_at":"2026-05-08 16:45:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":44742,"visible":true,"origin":"","legend":"\u003cp\u003eReceiver operating characteristic (ROC) curve showing predictive value of baseline EMW for CRT response.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9503125/v1/d07da47ebf57bf2577f54fba.png"},{"id":108822792,"identity":"c7beb23f-95f4-437d-9cbd-721e324e02c3","added_by":"auto","created_at":"2026-05-08 16:50:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":452320,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9503125/v1/26a53f06-1308-4cf9-8f10-d6672d9f6e2b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Electromechanical Window as an Integrative Marker of Remodeling and Arrhythmic Risk in Biventricular vs Left Bundle Branch Area Pacing","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCardiac resynchronization therapy (CRT) is an established treatment for patients with heart failure with reduced ejection fraction (HFrEF), electrical dyssynchrony, and persistent symptoms despite optimal medical therapy. Conventional CRT using biventricular (BiV) pacing improves ventricular synchrony, promotes reverse remodeling, and reduces morbidity and mortality; however, up to one-third of patients remain non-responders, underscoring the need for more physiological pacing strategies and improved markers of electromechanical recovery.\u0026sup1;⁻\u0026sup3;\u003c/p\u003e \u003cp\u003eLeft bundle branch area pacing (LBBAP) has emerged as a form of conduction system pacing capable of achieving near-normal ventricular activation through engagement of the His\u0026ndash;Purkinje system. Compared with conventional BiV pacing, LBBAP produces narrower QRS complexes and may result in superior mechanical synchrony and ventricular remodeling. Early observational studies and multicenter registries suggest that LBBAP-based CRT may offer improved electrical resynchronization and favorable echocardiographic response.⁴⁻⁷\u003c/p\u003e \u003cp\u003eWhile electrical resynchronization is commonly assessed using QRS duration, this parameter does not fully capture the complex interplay between myocardial depolarization, repolarization, and mechanical contraction. The electromechanical window (EMW), defined as the difference between mechanical systole and electrical systole, has emerged as a noninvasive marker of electromechanical coupling. A negative EMW reflects delayed mechanical contraction relative to repolarization and has been associated with arrhythmic risk and myocardial dysfunction.⁸⁻\u0026sup1;\u0026sup1;\u003c/p\u003e \u003cp\u003eCRT has the potential to improve EMW by restoring coordinated ventricular contraction, yet the comparative effects of different pacing modalities on EMW remain poorly studied. Understanding whether physiologic pacing strategies such as LBBAP provide superior normalization of EMW may offer mechanistic insight into differences in remodeling and possibly arrhythmic risk. Therefore, this study compared the impact of BiV pacing and LBBAP on EMW and evaluated the relationship between EMW changes, CRT response, reverse ventricular remodeling, and arrhythmic burden.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eThis prospective, single-center observational study enrolled 80 consecutive patients with HFrEF who underwent device implantation for CRT between January 2023 and June 2025. Eligible patients had left ventricular ejection fraction (LVEF) of 35% or less, New York Heart Association functional class II\u0026ndash;IV symptoms despite guideline-directed medical therapy, and a QRS duration\u0026thinsp;\u0026ge;\u0026thinsp;130 ms with left bundle branch block morphology or \u0026ge;\u0026thinsp;150 ms with non\u0026ndash;left bundle branch block morphology. Exclusion criteria included permanent atrial fibrillation with uncontrolled ventricular rates, significant primary valvular disease requiring surgical intervention, prior CRT implantation, and inadequate echocardiographic imaging windows.\u003c/p\u003e \u003cp\u003ePatients underwent either conventional biventricular (BiV) pacing or left bundle branch area pacing (LBBAP) according to operator expertise and anatomical feasibility. BiV pacing was performed using standard right atrial, right ventricular, and coronary sinus left ventricular leads. LBBAP was achieved via transseptal lead deployment targeting the left bundle branch area. Conduction system capture was confirmed using standard electrocardiographic criteria, including right bundle branch block\u0026ndash;like morphology and short stimulus-to\u0026ndash;left ventricular activation time.\u003c/p\u003e \u003cp\u003eTransthoracic echocardiography with simultaneous electrocardiographic recording was performed at baseline and six months after implantation using a standardized acquisition protocol. Left ventricular volumes and ejection fraction were calculated using the Simpson biplane method, and global longitudinal strain (GLS) was assessed using speckle-tracking echocardiography. Mechanical systole was defined as the interval from QRS onset to aortic valve closure (AoC) measured using continuous-wave Doppler in the left ventricular outflow tract. Electrical systole was defined as the QT interval from QRS onset to the end of the T wave on the simultaneously recorded electrocardiogram. EMW was calculated as mechanical systole minus the QT interval (EMW\u0026thinsp;=\u0026thinsp;QAoC \u0026ndash; QT, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), with negative values indicating electromechanical uncoupling. All EMW measurements were averaged over three consecutive cardiac cycles to improve measurement accuracy and reduce beat-to-beat variability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe primary endpoint was the change in EMW at six months. Secondary endpoints included changes in QRS duration, GLS, left ventricular end-systolic volume (LVESV), and CRT response, defined as a\u0026thinsp;\u0026ge;\u0026thinsp;15% reduction in LVESV at follow-up. Device interrogation at six months was used to assess atrial and ventricular arrhythmic events.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eStatistical analyses were performed using standard statistical software. Continuous variables are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation and categorical variables as counts and percentages. Within-group changes from baseline to six months were assessed using paired t-tests or Wilcoxon signed-rank tests as appropriate. Between-group comparisons (BiV vs LBBAP) were performed using independent t-tests or Mann\u0026ndash;Whitney U tests. Categorical variables were compared using the chi-square or Fisher\u0026rsquo;s exact test.\u003c/p\u003e \u003cp\u003eCorrelations between changes in EMW and echocardiographic parameters were evaluated using Pearson or Spearman correlation coefficients. Multivariable linear regression analysis was performed to identify independent predictors of EMW improvement. Receiver operating characteristic (ROC) analysis was used to assess the ability of baseline EMW to predict CRT response. A two-tailed p value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eBaseline demographic, clinical, and echocardiographic characteristics were comparable between groups. The mean age of the study population was 62\u0026thinsp;\u0026plusmn;\u0026thinsp;10 years, and 72% were male. Baseline mean LVEF was 27.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.5%, mean LVESV was 155\u0026thinsp;\u0026plusmn;\u0026thinsp;35 mL, QRS duration was 163\u0026thinsp;\u0026plusmn;\u0026thinsp;19 ms, and electromechanical window (EMW) was \u0026minus;\u0026thinsp;37\u0026thinsp;\u0026plusmn;\u0026thinsp;21 ms. Both pacing groups had similar baseline parameters (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\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\u003eBaseline Characteristics\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=\"left\" 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=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAll Patients (n\u0026thinsp;=\u0026thinsp;80)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBiV Pacing (n\u0026thinsp;=\u0026thinsp;40)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLBBAP (n\u0026thinsp;=\u0026thinsp;40)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep value (BiV vs LBBAP)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e63\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e61\u0026thinsp;\u0026plusmn;\u0026thinsp;11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.38\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale sex (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e72%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e70%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e75%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.62\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLVEF (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e27\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLVESV (mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e155\u0026thinsp;\u0026plusmn;\u0026thinsp;35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e158\u0026thinsp;\u0026plusmn;\u0026thinsp;36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e152\u0026thinsp;\u0026plusmn;\u0026thinsp;34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQRS (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e163\u0026thinsp;\u0026plusmn;\u0026thinsp;19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e162\u0026thinsp;\u0026plusmn;\u0026thinsp;18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e165\u0026thinsp;\u0026plusmn;\u0026thinsp;20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEMW (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026minus;37\u0026thinsp;\u0026plusmn;\u0026thinsp;21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;36\u0026thinsp;\u0026plusmn;\u0026thinsp;20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;38\u0026thinsp;\u0026plusmn;\u0026thinsp;22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the LBBAP group, successful conduction system capture at implantation was achieved in 36 of 40 patients (90%) and at six-month follow-up, it was maintained in 34 of 40 patients (85%), with loss of capture in 2 patients and transition to myocardial septal pacing in 4 patients. In the BiV pacing group, left ventricular lead placement in lateral or posterolateral coronary sinus branches was achieved in 32 of 40 patients (80%), while the remaining patients had leads positioned in anterolateral or mid-cardiac veins due to anatomical constraints.\u003c/p\u003e \u003cp\u003eAt six months, both pacing strategies resulted in significant QRS narrowing; however, the reduction was greater with LBBAP (42\u0026thinsp;\u0026plusmn;\u0026thinsp;15 ms vs 28\u0026thinsp;\u0026plusmn;\u0026thinsp;13 ms, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). EMW improved significantly in both groups, with a greater degree of normalization in the LBBAP group (from \u0026minus;\u0026thinsp;38\u0026thinsp;\u0026plusmn;\u0026thinsp;22 ms to \u0026minus;\u0026thinsp;5\u0026thinsp;\u0026plusmn;\u0026thinsp;18 ms) compared with the BiV group (from \u0026minus;\u0026thinsp;36\u0026thinsp;\u0026plusmn;\u0026thinsp;20 ms to \u0026minus;\u0026thinsp;18\u0026thinsp;\u0026plusmn;\u0026thinsp;19 ms; between-group p\u0026thinsp;=\u0026thinsp;0.003). Improvements in LVEF, GLS, and LVESV were observed in both groups but were more pronounced with LBBAP (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\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\u003eSix-Month Electrical, Echocardiographic, and Clinical Outcomes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" 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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTime Point\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAll Patients (n\u0026thinsp;=\u0026thinsp;80)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBiV Pacing (n\u0026thinsp;=\u0026thinsp;40)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLBBAP (n\u0026thinsp;=\u0026thinsp;40)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep value (BiV vs LBBAP)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eQRS (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e128\u0026thinsp;\u0026plusmn;\u0026thinsp;17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e134\u0026thinsp;\u0026plusmn;\u0026thinsp;16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e123\u0026thinsp;\u0026plusmn;\u0026thinsp;14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChange\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;35\u0026thinsp;\u0026plusmn;\u0026thinsp;16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;28\u0026thinsp;\u0026plusmn;\u0026thinsp;13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026minus;42\u0026thinsp;\u0026plusmn;\u0026thinsp;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eEMW (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;12\u0026thinsp;\u0026plusmn;\u0026thinsp;19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;18\u0026thinsp;\u0026plusmn;\u0026thinsp;19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026minus;5\u0026thinsp;\u0026plusmn;\u0026thinsp;18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.004\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChange\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e+\u0026thinsp;26\u0026thinsp;\u0026plusmn;\u0026thinsp;18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e+\u0026thinsp;18\u0026thinsp;\u0026plusmn;\u0026thinsp;16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;33\u0026thinsp;\u0026plusmn;\u0026thinsp;17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.003\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLVEF (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e35\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e38\u0026thinsp;\u0026plusmn;\u0026thinsp;7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChange\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e+\u0026thinsp;9\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e+\u0026thinsp;7\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;11\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.004\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eGLS (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;14.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;13.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026minus;16.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChange\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;5.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;4.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026minus;6.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLVESV (mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e125\u0026thinsp;\u0026plusmn;\u0026thinsp;32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e134\u0026thinsp;\u0026plusmn;\u0026thinsp;34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e116\u0026thinsp;\u0026plusmn;\u0026thinsp;28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChange (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;19\u0026thinsp;\u0026plusmn;\u0026thinsp;11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;15\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026minus;22\u0026thinsp;\u0026plusmn;\u0026thinsp;11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCRT Response (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e50%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e70%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.048\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHARE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e40%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.048\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNSVT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e35%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eImprovement in EMW correlated with LVESV reduction (r\u0026thinsp;=\u0026thinsp;0.46, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), GLS improvement (r\u0026thinsp;=\u0026thinsp;0.42, p\u0026thinsp;=\u0026thinsp;0.002), LVEF improvement (r\u0026thinsp;=\u0026thinsp;0.39, p\u0026thinsp;=\u0026thinsp;0.004), and QRS narrowing (r\u0026thinsp;=\u0026thinsp;0.35, p\u0026thinsp;=\u0026thinsp;0.01), supporting its association with both electrical and mechanical recovery (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\u003eCorrelation of Change in EMW with Echocardiographic and Electrical Parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCorrelation Coefficient (r)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ep value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLVESV reduction (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLVEF improvement (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.004\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlobal longitudinal strain improvement\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQRS narrowing (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFinal EMW at 6 months (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eMultivariable linear regression analysis identified independent predictors of EMW improvement at six months. Greater LVESV reduction (β\u0026thinsp;=\u0026thinsp;0.34, p\u0026thinsp;=\u0026thinsp;0.001), GLS improvement (β\u0026thinsp;=\u0026thinsp;0.29, p\u0026thinsp;=\u0026thinsp;0.003), and use of LBBAP rather than BiV pacing (β\u0026thinsp;=\u0026thinsp;0.31, p\u0026thinsp;=\u0026thinsp;0.002) were independently associated with greater EMW normalization. Baseline EMW also independently predicted EMW change (β=\u0026minus;0.22, p\u0026thinsp;=\u0026thinsp;0.01), while QRS narrowing showed a weaker but significant association (β\u0026thinsp;=\u0026thinsp;0.18, p\u0026thinsp;=\u0026thinsp;0.02). The overall model explained 48% of the variance in EMW improvement (R\u0026sup2;=0.48, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMultivariable Linear Regression Analysis for Predictors of EMW Improvement\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStandardized β Coefficient\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eStandard Error\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ep value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLVESV reduction (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGLS improvement\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.003\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLBBAP vs BiV pacing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline EMW (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026minus;0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQRS narrowing (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eDevice interrogation at six months revealed a higher arrhythmic burden in the BiV group (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). High atrial rate episodes (HARE) occurred in 40% of BiV patients compared with 22% in the LBBAP group (p\u0026thinsp;=\u0026thinsp;0.048), and non-sustained ventricular tachycardia (NSVT) was observed in 35% versus 15%, respectively (p\u0026thinsp;=\u0026thinsp;0.03). Persistent EMW negativity at follow-up was associated with a higher incidence of NSVT, irrespective of pacing modality (45% in patients with persistent EMW negativity vs 18% in those with EMW normalization, p\u0026thinsp;=\u0026thinsp;0.01).\u003c/p\u003e \u003cp\u003eCRT response, defined as a\u0026thinsp;\u0026ge;\u0026thinsp;15% reduction in LVESV, occurred more frequently in the LBBAP group than in the BiV group (70% vs 50%, p\u0026thinsp;=\u0026thinsp;0.048). Baseline EMW was significantly more negative in responders than in non-responders (\u0026minus;\u0026thinsp;42\u0026thinsp;\u0026plusmn;\u0026thinsp;21 ms vs\u0026thinsp;\u0026minus;\u0026thinsp;29\u0026thinsp;\u0026plusmn;\u0026thinsp;18 ms, p\u0026thinsp;=\u0026thinsp;0.01). Responders demonstrated greater EMW normalization at follow-up (+\u0026thinsp;34\u0026thinsp;\u0026plusmn;\u0026thinsp;18 ms vs\u0026thinsp;+\u0026thinsp;16\u0026thinsp;\u0026plusmn;\u0026thinsp;14 ms, p\u0026thinsp;=\u0026thinsp;0.002) and less residual EMW negativity (\u0026minus;\u0026thinsp;8\u0026thinsp;\u0026plusmn;\u0026thinsp;17 ms vs\u0026thinsp;\u0026minus;\u0026thinsp;19\u0026thinsp;\u0026plusmn;\u0026thinsp;20 ms, p\u0026thinsp;=\u0026thinsp;0.01) (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Receiver operating characteristic analysis showed that baseline EMW predicted CRT response with moderate accuracy (AUC 0.71) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e); a cutoff value of \u0026minus;\u0026thinsp;35 ms provided 68% sensitivity and 70% specificity.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBaseline and Follow-Up Characteristics of CRT Responders vs Non-Responders\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" 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=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCRT Responders (n\u0026thinsp;=\u0026thinsp;48)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNon-Responders (n\u0026thinsp;=\u0026thinsp;32)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ep value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e61\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e63\u0026thinsp;\u0026plusmn;\u0026thinsp;11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale sex (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e73%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e69%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline LVEF (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline LVESV (mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e160\u0026thinsp;\u0026plusmn;\u0026thinsp;34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e148\u0026thinsp;\u0026plusmn;\u0026thinsp;36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline QRS (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e166\u0026thinsp;\u0026plusmn;\u0026thinsp;19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e159\u0026thinsp;\u0026plusmn;\u0026thinsp;17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaseline EMW (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026minus;42\u0026thinsp;\u0026plusmn;\u0026thinsp;21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;29\u0026thinsp;\u0026plusmn;\u0026thinsp;18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEMW change at 6 months (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e+\u0026thinsp;34\u0026thinsp;\u0026plusmn;\u0026thinsp;18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e+\u0026thinsp;16\u0026thinsp;\u0026plusmn;\u0026thinsp;14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFinal EMW (ms)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026minus;8\u0026thinsp;\u0026plusmn;\u0026thinsp;17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;19\u0026thinsp;\u0026plusmn;\u0026thinsp;20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLVEF improvement (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e+\u0026thinsp;13\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e+\u0026thinsp;4\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLVESV reduction (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026minus;28\u0026thinsp;\u0026plusmn;\u0026thinsp;8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;6\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGLS improvement\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026minus;7.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNSVT at 6 months (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e38%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eStructural and functional recovery were also more pronounced among responders, with larger improvements in LVEF (+\u0026thinsp;13\u0026thinsp;\u0026plusmn;\u0026thinsp;6% vs\u0026thinsp;+\u0026thinsp;4\u0026thinsp;\u0026plusmn;\u0026thinsp;3%, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), greater LVESV reduction (\u0026minus;\u0026thinsp;28\u0026thinsp;\u0026plusmn;\u0026thinsp;8% vs\u0026thinsp;\u0026minus;\u0026thinsp;6\u0026thinsp;\u0026plusmn;\u0026thinsp;5%, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), and greater improvement in global longitudinal strain (\u0026minus;\u0026thinsp;7.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1 vs\u0026thinsp;\u0026minus;\u0026thinsp;2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.6, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Non-responders exhibited a higher incidence of NSVT at follow-up (38% vs 17%, p\u0026thinsp;=\u0026thinsp;0.03), while baseline demographic and clinical characteristics were otherwise similar between groups (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study demonstrates that both conventional BiV pacing and LBBAP improve electromechanical coupling, as reflected by a shift of EMW toward less negative values. However, LBBAP produced significantly greater EMW normalization, more pronounced reverse remodeling, and superior electrical resynchronization at six months. These findings extend growing evidence that conduction system pacing restores more physiological ventricular activation than conventional epicardial left ventricular stimulation.⁴⁻⁷ Importantly, our results indicate that the advantages of LBBAP extend beyond QRS narrowing to more complete restoration of global electromechanical timing.\u003c/p\u003e \u003cp\u003eThe electromechanical window integrates electrical repolarization and mechanical systole into a single parameter, thereby reflecting overall electromechanical interaction rather than isolated electrical or mechanical phenomena. A negative EMW has been associated with arrhythmic risk in long QT syndrome, cardiomyopathies, and acquired repolarization disorders.⁸⁻\u0026sup1;\u0026sup1; In the context of CRT, EMW improvement likely represents better temporal alignment between depolarization, repolarization, and myocardial contraction. The greater EMW normalization observed with LBBAP suggests that activation through the native His\u0026ndash;Purkinje system more effectively restores this delicate electromechanical balance.\u003c/p\u003e \u003cp\u003eConsistent with prior studies, LBBAP achieved greater QRS narrowing and more favorable improvements in LVEF, LVESV, and GLS compared with BiV pacing.⁵⁻⁷,\u0026sup1;\u0026sup2; While earlier investigations primarily emphasized electrical and volumetric outcomes, our study adds mechanistic insight by demonstrating that EMW improvement parallels structural and functional recovery. Correlation analysis showed that EMW normalization was associated with LVESV reduction, GLS improvement, LVEF improvement, and QRS narrowing, supporting the concept that EMW reflects integrated electromechanical recovery rather than electrical resynchronization alone.\u003c/p\u003e \u003cp\u003eMultivariable analysis further strengthened this interpretation, demonstrating that EMW improvement was independently associated with reverse remodeling, myocardial strain recovery, and pacing modality. Importantly, LBBAP remained an independent determinant of EMW normalization even after adjustment for changes in QRS duration and ventricular function, suggesting that conduction system pacing confers intrinsic electromechanical advantages beyond simple electrical shortening.\u003c/p\u003e \u003cp\u003eOur study also highlights the predictive role of EMW. Patients with more negative baseline EMW values were more likely to exhibit CRT response, and baseline EMW demonstrated moderate discriminative ability for predicting reverse remodeling. Responders showed greater EMW normalization and less residual EMW negativity at follow-up, along with larger improvements in LVEF, LVESV, and GLS. These findings suggest that EMW may serve not only as a marker of treatment effect but also as a potential tool for identifying patients most likely to benefit from CRT.\u003c/p\u003e \u003cp\u003eImportantly, electromechanical recovery appeared closely linked to arrhythmic risk. Device interrogation revealed a higher burden of atrial and ventricular arrhythmias in the BiV group, paralleling the lesser degree of EMW normalization observed in these patients. Moreover, persistent EMW negativity at six months was associated with a significantly higher incidence of non-sustained ventricular tachycardia compared with EMW normalization (45% vs 18%), irrespective of pacing modality. Similarly, CRT non-responders\u0026mdash;who exhibited less EMW improvement and greater residual EMW negativity\u0026mdash;had a higher burden of NSVT. These findings support the concept that incomplete restoration of electromechanical synchrony reflects ongoing dispersion of repolarization and mechanical dyssynchrony, creating a substrate vulnerable to ventricular arrhythmias.\u003c/p\u003e \u003cp\u003eFrom a clinical perspective, EMW may represent a novel integrative biomarker linking electrical resynchronization, mechanical recovery, and arrhythmic vulnerability. Traditional CRT assessment relies heavily on QRS duration and volumetric response, which do not consistently capture arrhythmic risk or electromechanical stability. EMW offers a noninvasive measure that bridges electrical and mechanical domains and may provide incremental value for comparing pacing strategies, identifying CRT responders, and recognizing patients at continued arrhythmic risk despite therapy.\u0026sup1;\u0026sup3;,\u0026sup1;⁴\u003c/p\u003e \u003cp\u003eAlthough our study was not powered for definitive clinical arrhythmic endpoints, the consistent association between EMW normalization, reverse remodeling, and reduced ventricular arrhythmia burden raises the hypothesis that conduction system pacing may confer anti-arrhythmic benefit by restoring electromechanical synchrony more effectively than conventional BiV pacing. This mechanistic link warrants validation in larger prospective studies with long-term adjudicated arrhythmic and survival outcomes.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn patients with heart failure undergoing cardiac resynchronization therapy, left bundle branch area pacing resulted in greater normalization of the electromechanical window and superior reverse ventricular remodeling compared with conventional biventricular pacing. Improvement in EMW correlated with reductions in LV end-systolic volume and improvements in myocardial strain, supporting its role as an integrative marker of electromechanical recovery rather than electrical resynchronization alone. Baseline EMW negativity predicted CRT response, and persistent EMW abnormalities were associated with a higher burden of device-detected ventricular arrhythmias, suggesting that EMW may also reflect residual arrhythmic substrate.\u003c/p\u003e \u003cp\u003eThese findings highlight the electromechanical window as a promising noninvasive physiological marker that links electrical activation, mechanical recovery, and arrhythmic vulnerability. Incorporation of EMW assessment into CRT evaluation may improve patient selection, aid comparison of pacing strategies, and help identify individuals at continued arrhythmic risk despite therapy. Larger multicenter studies with long-term clinical outcomes are warranted to validate EMW-guided approaches in cardiac resynchronization therapy.\u003c/p\u003e\n\u003ch3\u003eLimitations and Further Considerations\u003c/h3\u003e\n\u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eSingle-center, nonrandomized design with potential selection bias\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eModest sample size not powered for hard clinical outcomes\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eShort follow-up duration (6 months)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eLack of standardized device optimization protocols across patients\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eEMW measurement not yet widely standardized; possible interobserver variability\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eNo assessment of long-term arrhythmic events or ICD therapies\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eAbsence of advanced imaging (e.g., CMR) to evaluate scar and fibrosis\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eFindings require validation in multicenter randomized trials\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eFuture studies should assess whether EMW-guided CRT optimization improves outcomes\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; BiV\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eBiventricular\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; CRT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eCardiac Resynchronization Therapy\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; EMW\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eElectromechanical Window\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; GLS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eGlobal Longitudinal Strain\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; HARE\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eHigh Atrial Rate Episodes\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; HFrEF\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eHeart Failure with Reduced Ejection Fraction\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; LBBAP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eLeft Bundle Branch Area Pacing\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; LV\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eLeft Ventricle / Left Ventricular\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; LVEF\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eLeft Ventricular Ejection Fraction\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; LVESV\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eLeft Ventricular End\u0026ndash;Systolic Volume\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; NSVT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNon\u0026ndash;Sustained Ventricular Tachycardia\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; NYHA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNew York Heart Association\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; QRS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eQRS Complex\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u0026bull; ROC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eReceiver Operating Characteristic\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDeclaration of generative AI and AI-assisted technologies in the manuscript preparation process\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDuring the preparation of this work the author(s) used ChatGPT in order to paraphrase few sentences. After using this tool/service, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the published article.\u003c/p\u003e\n\u003cp\u003eEthics declarations\u003c/p\u003e\n\u003cp\u003eEthics approval and consent to participate\u003c/p\u003e\n\u003cp\u003eThe study was carried out in accordance with the principles of the Declaration of Helsinki and was approved by Pragma Medical Institute\u0026rsquo;s Institutional Ethics Committee (IEC/2024/004). Written informed consent was taken for each participant.\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eA.K. wrote the main manuscript text and T.B. and S.J. helped in data collection and analysis. All authors reviewed the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMcDonagh TA et al (2021) 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. Eur Heart J\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWriting Committee Members (2022) 2022 AHA/ACC/HFSA Guideline for the Management of Heart Failure. Circulation\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCleland JGF et al (2005) The effect of cardiac resynchronization on morbidity and mortality in heart failure. N Engl J Med\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang W et al (2020) Left bundle branch pacing: current knowledge and future prospects. JACC Clin Electrophysiol\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJastrzębski M et al (2022) Left bundle branch area pacing outcomes: results from the MELOS registry. Eur Heart J\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVijayaraman P et al (2021) Conduction system pacing. J Am Coll Cardiol\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu S et al (2023) Left bundle branch pacing vs biventricular pacing for CRT: a multicenter comparison. Heart Rhythm\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTer Bekke RMA, Volders PGA (2020) The electromechanical window: a novel marker of arrhythmic risk. Heart Rhythm\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOdening KE et al (2021) Electromechanical reciprocity and arrhythmogenesis. Eur Heart J\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDeissler PM, Volders PGA, Ter Bekke RMA (2025) The electromechanical window for arrhythmia-risk assessment. Heart Rhythm 22(1):118\u0026ndash;127. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.hrthm.2024.06.012\u003c/span\u003e\u003cspan address=\"10.1016/j.hrthm.2024.06.012\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003eEpub 2024 Jun 13. PMID: 38878938\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRhee TM et al (2023) Predictive value of electromechanical window for ventricular arrhythmia. J Korean Med Sci\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSharma PS et al (2022) Permanent His bundle pacing and LBB pacing for CRT. JACC Clin Electrophysiol\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMafi-Rad M et al (2016) Mechanical dyssynchrony and CRT response. Europace\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUpadhyay GA et al (2015) On-treatment QRS narrowing and CRT outcomes. Circulation\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"the-egyptian-heart-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"tehj","sideBox":"Learn more about [The Egyptian Heart Journal](https://tehj.springeropen.com)","snPcode":"43044","submissionUrl":"https://submission.springernature.com/new-submission/43044/3","title":"The Egyptian Heart Journal","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Electromechanical window, Cardiac resynchronization therapy, Left bundle branch area pacing, Ventricular remodelling, Arrhythmia","lastPublishedDoi":"10.21203/rs.3.rs-9503125/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9503125/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eThe electromechanical window (EMW), defined as difference between mechanical and electrical systole, is an emerging marker of arrhythmic risk and ventricular dysfunction. Although cardiac resynchronization therapy (CRT) improves mechanical synchrony, the influence of different pacing strategies on EMW is not well established. Left bundle branch area pacing (LBBAP) provides more physiological ventricular activation than biventricular (BiV) pacing. This study compared the effects of BiV pacing and LBBAP on EMW and examined its association with CRT response and arrhythmic burden.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eIn this prospective study, 80 patients with LVEF\u0026thinsp;\u0026le;\u0026thinsp;35% undergoing CRT were assigned to BiV pacing (n\u0026thinsp;=\u0026thinsp;40) or LBBAP (n\u0026thinsp;=\u0026thinsp;40). Echocardiography with simultaneous ECG was performed at baseline and 6 months. EMW was calculated as the interval from QRS onset to aortic valve closure minus the QT interval. Secondary measures included QRS duration, global longitudinal strain (GLS), left ventricular end-systolic volume (LVESV), and LVEF. CRT response was defined as \u0026ge;\u0026thinsp;15% reduction in LVESV.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eLBBAP achieved greater QRS narrowing and larger EMW improvement than BiV pacing. EMW improvement correlated with LVESV reduction (r\u0026thinsp;=\u0026thinsp;0.46, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and GLS improvement (r\u0026thinsp;=\u0026thinsp;0.42, p\u0026thinsp;=\u0026thinsp;0.002). CRT response was more frequent with LBBAP (70% vs 50%, p\u0026thinsp;=\u0026thinsp;0.048). Baseline EMW predicted CRT response (AUC 0.71; cutoff\u0026thinsp;\u0026minus;\u0026thinsp;35 ms: 68% sensitivity, 70% specificity). Persistent EMW negativity was associated with higher non-sustained ventricular tachycardia incidence (45% vs 18%, p\u0026thinsp;=\u0026thinsp;0.01).\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eLBBAP provides greater EMW normalization and reverse remodeling than BiV pacing. EMW correlates with structural recovery and may serve as a physiological marker of CRT response and arrhythmic vulnerability.\u003c/p\u003e","manuscriptTitle":"Electromechanical Window as an Integrative Marker of Remodeling and Arrhythmic Risk in Biventricular vs Left Bundle Branch Area Pacing","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-08 16:27:35","doi":"10.21203/rs.3.rs-9503125/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-04-24T10:00:24+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-23T09:49:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-23T09:48:34+00:00","index":"","fulltext":""},{"type":"submitted","content":"The Egyptian Heart Journal","date":"2026-04-23T06:46:14+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"the-egyptian-heart-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"tehj","sideBox":"Learn more about [The Egyptian Heart Journal](https://tehj.springeropen.com)","snPcode":"43044","submissionUrl":"https://submission.springernature.com/new-submission/43044/3","title":"The Egyptian Heart Journal","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2cb6cab7-a415-47c1-9c37-3a9d40d9c518","owner":[],"postedDate":"May 8th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-08T16:27:36+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-08 16:27:35","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9503125","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9503125","identity":"rs-9503125","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}