Monitoring anti-factor Xa activity in patients with chronic thromboembolic pulmonary hypertension treated with factor Xa inhibitors

Monitoring anti-factor Xa activity in patients with chronic thromboembolic pulmonary hypertension treated with factor Xa inhibitors | 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 Article Monitoring anti-factor Xa activity in patients with chronic thromboembolic pulmonary hypertension treated with factor Xa inhibitors Yoshihisa Nakano, Shiro Adachi, Miku Hirose, Takeshi Adachi, Itsumure Nishiyama, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4893570/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Oct, 2024 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract Direct oral anticoagulants (DOACs) have been used clinically in patients with chronic thromboembolic pulmonary hypertension (CTEPH) for secondary prevention after acute venous thromboembolism, although the data is limited. We evaluated the effects of DOACs—especially factor Xa (FXa) inhibitors—by measuring anti-factor Xa activity (AXA). Fifty consecutive CTEPH patients treated with either rivaroxaban, apixaban, or edoxaban were enrolled. Heparin-calibrated AXA was measured at both peak and trough. The median peak heparin-calibrated AXA across all 50 patients was 1.90 IU/mL and was comparable among the three FXa inhibitors. At trough, heparin-calibrated AXA was significantly higher in apixaban treated patients (median 0.70 IU/mL) than in those with rivaroxaban (median 0.11 IU/mL) or edoxaban (median 0.11 IU/mL, p <.001). Peak heparin-calibrated AXA was significantly lower with reduced-dose FXa inhibitor (edoxaban 30 mg/day) than with the reference dose (edoxaban 60 mg/day, apixaban 10 mg/day, or rivaroxaban 15 mg/day, p =.01). The heparin-calibrated AXA of both rivaroxaban and apixaban was strongly significantly correlated with the plasma concentration of each drug. The cumulative rate of major and clinically relevant non-major bleeding was significantly higher in patients with peak heparin-calibrated AXA ≥2.09 IU/mL. Heparin-calibrated AXA could provide useful information when treating CTEPH patients with FXa inhibitors. Health sciences/Cardiology/Cardiovascular biology/Cardiovascular diseases Health sciences/Diseases/Cardiovascular diseases/Vascular diseases/Thromboembolism factor Xa direct-acting oral anticoagulant pulmonary thromboembolism pulmonary hypertension Chronic thromboembolic pulmonary hypertension Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Chronic thromboembolic pulmonary hypertension (CTEPH) is characterized by persistent organized thrombi of the pulmonary artery and pulmonary hypertension. Therefore, lifelong anticoagulation therapy is indispensable for CTEPH patients. For a period of years, vitamin-K antagonists (VKAs)—mostly warfarin—were the only oral anticoagulants available. Nowadays, the efficacy and safety of direct oral anticoagulants (DOACs) in patients with non-valvular atrial fibrillation (NVAF) or acute venous thromboembolism (VTE) have proven to be non-inferior, or superior, to VKAs. 1–6 However, data on the efficacy and safety of DOACs in CTEPH patients remain limited. KABUKI Trial was the first randomized phase Ⅲ trial that reported the non-inferiority of edoxaban to warfarin in CTEPH patients, although further large-scale multinational long-term study is warranted. 7 In contrast, a UK retrospective study reported that the efficacy and safety of DOACs were comparable to those of VKAs in operable CTEPH patients. 9 Furthermore, although laboratory monitoring of DOACs is basically unnecessary, it is essential to objectively evaluate these drugs’ actions in any investigation of their efficacy and safety. Previous studies have recommended measuring plasma drug concentrations to monitor DOAC effects, and anti-factor Xa activity (AXA) has also been reported as a convenient method of monitoring factor Xa (FXa) inhibitors. 10–13 Therefore, here, we aimed to evaluate the pharmacological effects of FXa inhibitors by measuring heparin-calibrated AXA in patients with CTEPH. In addition, we also aimed to assess the relation of heparin-calibrated AXA value and risk of clinical events. Materials and methods Study population This was a single-center observational study. We screened 164 Japanese patients who were diagnosed with, and treated for, CTEPH at our institution from 2010 to 2021 (Fig. 1 ). The patients were treated with the VKA warfarin or with the FXa inhibitors rivaroxaban, apixaban, or edoxaban. Among those treated with FXa inhibitors, we enrolled 50 consecutive patients who visited our hospital for detailed examination from April 2021 to December 2021. All 50 patients provided written informed consent. This study was conducted in accordance with the Declaration of Helsinki and the ethical standards of the institutional committee on human experimentation, and it was approved by the Human Research Ethics Committees of Nagoya University Hospital (no. 2020 − 0615). Definition Chronic pulmonary thrombi or chronic perfusion obstruction was confirmed by either enhanced computed tomography or perfusion scan after at least 3 months of effective anticoagulation. Pulmonary hypertension was defined as mean pulmonary arterial pressure (PAP) ≥ 25 mmHg and pulmonary arterial wedge pressure (PAWP) ≤ 15 mmHg according to the 2015 European Society of Cardiology/ European Respiratory Society guidelines for the diagnosis and treatment of pulmonary hypertension. 14 Thus, CTEPH was diagnosed when patients met the conditions of both chronic pulmonary thrombi and pulmonary hypertension. Right heart catheterization was performed within median 3 days before or after blood collection. PAWP, PAP, right ventricular pressure, and right atrial pressure were measured. Cardiac output was calculated by using the Fick method, and pulmonary vascular resistance (PVR) was calculated by using the standard formula: PVR = (mean PAP − mean PAWP)/cardiac output. Anticoagulants and measurement of coagulation function The FXa inhibitor used was selected according to the decision of each attending physician. The dosage was decided according to the description of the Japan Pharmaceutical Reference, namely 15 mg once per day for rivaroxaban, 5 mg twice per day for apixaban, and 60 mg or 30 mg once per day for edoxaban. All patients had received continuous anticoagulation therapy with the same drug at least 30 days before heparin-calibrated AXA measurement. Heparin-calibrated AXA, prothrombin time, and activated partial thromboplastin time were examined twice: at trough and peak. In accordance with previous reports, we defined the trough time as immediately before the administration of any FXa inhibitor. 12,13 We defined the peak time as 2 h after drug administration in patients taking edoxaban and 3 h after in those taking rivaroxaban or apixaban. 12,13 To ensure that blood was collected accurately at the trough and peak times, we collected it by using the following procedure: outpatients brought their anticoagulant drug to the outpatient clinic instead of taking it at home and took the tablet at the clinic just after their first blood collection; in the case of inpatients, ward staff managed the time of intake. Blood samples were centrifuged at 3000 g for 5 min, and platelet-poor plasma was frozen at − 80°C until the AXA analysis was performed. AXA was measured with a HemosIL Liquid Heparin Kit (Instrumentation Laboratory, Lexington, KY, USA) and HemosIL Heparin Calibrators on an ACL TOP hemostasis test system (Werfen, Bedford, MA, USA). This test is a one-stage assay consisting of incubation of a diluted plasma sample with a substrate of FXa to measure the optical density at a wavelength of 405 nm after the addition of bovine FXa. The optical density is measured on the ACL TOP instrument. At the same time, we measured the plasma concentration of apixaban with HemosIL Apixaban Calibrators and that of rivaroxaban with HemosIL Rivaroxaban Calibrators, respectively (Instrumentation Laboratory). 15 Since there were no edoxaban calibrator that was commercially available, we could not confirm the plasma concentration of edoxaban. Retrospective analysis The medical records of all 50 patients from the time of initiation of the FXa inhibitor to the day of heparin-calibrated AXA measurement were retrospectively reviewed. Recurrent VTE was defined as newly diagnosed of either deep vein thrombosis, pulmonary embolism, or as an exacerbation CTEPH, or any combination of these, with or without symptoms, as confirmed by the detection of new or exacerbated thrombus on imaging examination. Major bleeding and clinically relevant non-major bleeding (CRNMB) were defined according to the criteria of the International Society on Thrombosis and Haemostasis. 16–18 Major bleeding was diagnosed when at least one of the following criteria was met: bleeding associated with a ≥ 2 g/dL decrease in hemoglobin level, bleeding leading to ≥ 2 units of blood transfusion, symptomatic bleeding in a critical area or organ, or fatal bleeding. CRNMB was diagnosed as clinically overt bleeding that did not meet the criteria for major bleeding but that required medical intervention, hospitalization, increased level of care, or face-to-face evaluation. Statistical analysis Continuous data are presented as medians and interquartile ranges, and categorical data are presented as numbers and percentages. Data of heparin-calibrated AXA were presented as median and 5th to 95th percentiles (with the exception of three cases, in which the 25th to 75th percentiles and 10th to 90th percentiles were used because of the limited numbers of participants; see Table 2 ). Continuous data were compared between two groups by using the Mann–Whitney U -test, or among three or more groups by using the Kruskal–Wallis test. The post-hoc analysis was adjusted for Bonferroni correction. Categorical data were compared by using the chi-square test or Fisher’s exact test, depending on the distribution of the data. Correlation analysis was performed by using Spearman’s rank correlation owing to the distribution of the data. A receiver operating characteristic (ROC) analysis was used to determine the cutoff value of the peak heparin-calibrated AXA level as a predictor of bleeding events. The cutoff value was determined as the point on the ROC curve closest to (0,1). 19 The Kaplan–Meier method was used to estimate cumulated bleeding rates, and differences between groups were evaluated by using the log-rank method. Multi-variate cox proportional-hazards model adjusted by age and presence of invasive treatment was performed to determine the hazard ratio (HR) and 95% confidence intervals (CI) of bleeding events between two groups. A p -value of < .05 was considered statistically significant. Statistical analyses were conducted by using Stata version 17 (Stata Corp, College Station, Texas, USA) and the SPSS statistical software program (version 27.0 for Windows; SPSS, Chicago, IL, USA). Table 1 Characteristics of the 50 patients at baseline Age, years 63 ± 14 Male, n (%) 21 (42) Body weight, kg 62.1 ± 15.8 Body surface area, m 2 1.63 ± 0.24 History of definitively diagnosed acute pulmonary embolism, n (%) 25 (50) History of deep vein thrombosis, n (%) 23 (46) Active cancer a , n (%) 2 (4) Thrombophilia, n (%) 1 (2) Cardiovascular disease, n (%) 2 (4) Chronic lung disease, n (%) 9 (18) Type of CTEPH at diagnosis Central CTEPH 13 (26) Peripheral CTEPH 37 (74) Invasive treatment, n (%) Pulmonary endarterectomy 7 (14) Balloon pulmonary angioplasty 29 (58) Use of oral pulmonary vasodilator (riociguat), n (%) 32 (64) WHO functional class (1/2/3/4), n (%) 4/39/7/0 (8/78/14/0) Laboratory parameters Creatinine clearance S b , mL/min 68.0 (54.4–104.9) Hemoglobin, g/dL 13.5 ± 1.7 Platelets, ×10 4 27.8 ± 11.2 D-dimer, µg/mL 0.52 ± 0.08 Fibrin monomer complex 3.35 ± 1.74 Thrombin antithrombin complex 0.9 (0.6–1.4) Prothrombin fragment 1 + 2 147.5 (111.3–184.5) Troponin T, ng/mL 0.007 (0.005–0.012) BNP, pg/mL 9.7 (5.8–26.7) Echocardiography c LVDd, mm 42.1 ± 6.1 LVEF, % 68.0 ± 5.8 TRPG, mmHg 39.0 (28.8–54.9) TAPSE, mm 17.8 ± 4.2 Hemodynamics Mean PAP, mmHg 30 ± 11 RAP, mmHg 7 ± 3 CI, L/min/m 2 2.2 ± 0.5 PVR, Wood units 5.0 (3.3–8.1) Anticoagulant used, n (%) Edoxaban 10 (20) Apixaban 14 (28) Rivaroxaban 26 (52) BNP, brain natriuretic peptide; CI, cardiac index; LVDd, left ventricular end-diastolic diameter; LVEF, left ventricular ejection fraction; PAP, pulmonary arterial pressure; PVR, pulmonary vascular resistance; RAP, right atrial pressure; TAPSE, tricuspid annular plane systolic excursion; TRPG, tricuspid regurgitation pressure gradient Categorical variables are presented as numbers and percentages, and continuous variables are presented as means ± standard deviation or medians and interquartile range. a Active cancer was defined as any cancer, including locally recurrent, regionally advanced, or metastatic cancer, that had been diagnosed or treated in the 6 months before the enrollment b Creatinine clearance was calculated by using the Cockcroft–Gault equation. c echocardiography was performed in limited participants (n = 39) nearly before or after heparin-calibrated AXA measurement. Table 2 Coagulation markers at trough and peak Trough Peak p value Prothrombin time, s 11.5 ± 0.7 13.3 ± 1.4 < .001 Activated partial thromboplastin time, s 31.7 ± 3.8 37.5 ± 6.1 < .001 Heparin-calibrated AXA in all patients, IU/mL a 0.14 (0.02–1.54) 1.90 (0.84–3.07) < .001 Heparin-calibrated AXA for rivaroxaban, IU/mL a 0.11 (0.05–0.50) 1.98 (0.89–3.08) < .001 Heparin-calibrated AXA for edoxaban, IU/mL a 0.11 (0.01–0.30) e 1.59 (0.46–2.43) e .005 Heparin-calibrated AXA for apixaban, IU/mL a 0.70 (0.23–1.92) e 2.04 (1.16–3.86) e < .001 Heparin-calibrated AXA for once daily FXa inhibitors, IU/mL a 0.11 (0.01–0.36) 1.87 (0.76–3.06) < .001 Heparin-calibrated AXA for reference dose of FXa inhibitor, IU/mL b 0.14 (0.02–1.67) 1.95 (0.91–3.09) < .001 Heparin-calibrated AXA for reduced dose of FXa inhibitor, IU/mL b 0.11 (0.07–0.23) f 1.25 (0.77–1.70) f .04 Apixaban plasma concentration c , ng/mL 116.2 (58.8–362.1) e 273.2 (181.7–564.8) e < .001 Rivaroxaban plasma concentration d , ng/mL 15.4 (2.2–69.3) 216.2 (119.2–457.8) < .001 AXA, anti-factor Xa activity; FXa, factor Xa. Numbers are described as means ± standard deviation, or medians (5th to 95th percentiles). a Heparin-calibrated AXA was measured in all 50 patients: 26 on rivaroxaban, 14 on apixaban, and 10 on edoxaban. Once-daily factor-Xa inhibitor included was rivaroxaban or edoxaban (n = 36). b Reference dose represented rivaroxaban 15 mg/day, apixaban 10 mg/day, or edoxaban 60 mg/day (n = 45). Reduced dose represented edoxaban 30 mg/day (n = 5). c Apixaban drug concentration was measured in 14 patients taking apixaban. d Rivaroxaban drug concentration was measured in 26 patients taking rivaroxaban. e As the number of participants was limited, the 10th and 90th percentiles are described. f As the number of participants was limited, the 25th and 75th percentiles are described. Results The mean age of the 50 patients evaluated was 63 ± 14 years, and 42% were male (Table 1 ). A history of VTE (pulmonary embolism plus deep vein thrombosis, deep vein thrombosis alone, or pulmonary embolism alone) was reported by 66% of patients, and 50% of patients had a history of acute pulmonary embolism. Along with anticoagulation therapy, a pulmonary vasodilator (riociguat) was used in 64% of patients, and invasive treatment (pulmonary endarterectomy [PEA] or balloon pulmonary angioplasty [BPA], or both) was performed in 70% of patients (including one who underwent both procedures) at the time of AXA measurement. The serum D-dimer level was 1.0 µg/mL or lower in all patients, suggesting that none of them was in a hypercoagulability state. The median heparin-calibrated AXA across all 50 patients was significantly higher at peak (1.90 IU/mL) than at trough (0.14 IU/mL, p < .001, Table 2 and Fig. 2 a). We then compared the heparin-calibrated AXA values between pairs of FXa inhibitors. The trough heparin-calibrated AXA was significantly higher in patients treated with apixaban than in those given rivaroxaban or edoxaban (Table 2 and Fig. 2 b, p < .001). In contrast, the peak heparin-calibrated AXA values were comparable among the three groups (Fig. 2 b, p = .09). In addition, when we defined edoxaban 30 mg/day as a reduced dose and all the other doses (edoxaban 60 mg/day, apixaban 10 mg/day, and rivaroxaban 15 mg/day) as the reference dose, the peak heparin-calibrated AXA was significantly lower in the reduced-dose group ( p = .01, Fig. 2 c). Among the 26 patients treated with rivaroxaban, the plasma concentration of the drug was significantly higher at peak (median 216.2 ng/mL) than at trough (median 15.4 ng/mL, p < .001, Table 2 , Fig. 3 a). To confirm the accuracy of the heparin-calibrated AXA, we analyzed its relationship with the plasma rivaroxaban concentration. The two sets of data were very strongly correlated ( R = .957, p < .001; Fig. 3 b). Among the 14 patients treated with apixaban, the plasma concentration of the drug was significantly higher at peak (median 273.2 ng/mL) than at trough (median 116.2 ng/mL, p < .001, Table 2 and Fig. 4 a). The heparin-calibrated AXA value and the plasma concentration of apixaban were very strongly correlated ( R = .980, p < .001; Fig. 4 b). Furthermore, we confirmed the correlation between heparin-calibrated AXA and plasma concentration separately at trough and peak for each drug; we found strong correlations in the cases of both rivaroxaban and apixaban (Supplementary Figs. 1, 2: all p < .001). We then analyzed the relationship between renal function and heparin-calibrated AXA (Fig. 5 ). Peak heparin-calibrated AXA and creatinine clearance (CCr) were significantly negatively correlated ( R = –.314, p = .03) (Fig. 5 a), whereas there was no correlation between CCr and heparin-calibrated AXA at trough in the case of the once-daily anticoagulants (rivaroxaban and edoxaban, p = .19; Fig. 5 b) or the twice daily anticoagulant (apixaban, p = .08; Fig. 5 c). Among the 50 patients, no recurrent VTE occurred, major bleeding events occurred in four, and CRNMB occurred in three during the observational period of median 787 (Interquartile range, 487–1334) days. We performed an ROC analysis to determine the cutoff points of the peak heparin-calibrated AXA level for bleeding events, for which the area under curve was 0.79 (Fig. 6 ). The sensitivity and specificity of the cutoff point of a peak heparin-calibrated AXA of 2.09 IU/mL were 86% and 72%, respectively. We then used this cutoff point to perform a Kaplan–Meier analysis of major bleeding and CRNMB events. The cumulative rate of major bleeding and CRNMB adjusted by age and presence of invasive treatment was significantly higher in patients with peak heparin-calibrated AXA ≥ 2.09 IU/mL than in patients with values below this point (HR 11.5 [95% CI: 1.3–105.2], Fig. 6 ). Discussion We report four main findings from this study of CTEPH patients. First, peak heparin-calibrated AXA was significantly higher than trough with all three FXa inhibitors, and the trough heparin-calibrated AXA of apixaban was significantly higher than that of rivaroxaban or edoxaban, reflecting the twice-daily dosing of apixaban. Secondly, peak heparin-calibrated AXA was significantly lower with the reduced-dose FXa inhibitor than with the reference dose. Thirdly, heparin-calibrated AXA was very strongly correlated with the plasma concentrations of rivaroxaban and apixaban. Lastly, major bleeding and CRNMB occurred significantly in patients with peak heparin-calibrated AXA ≥ 2.09 IU/mL. In recent years, DOACs have proven to be at least non-inferior to VKAs in patients with VTE. 1–3 However, DOACs are contraindicated in patients with mechanical heart valves or with anti-phospholipid syndrome. 20–22 In patients with CTEPH, lifelong anticoagulation with sufficient effect is the most fundamental and important treatment, as these patients are at high risk of the clinical condition of VTE. Therefore, although DOACs are used in CTEPH patients worldwide for secondary prevention of VTE (despite their still not being strictly recommended for use in these patients), we need to carefully validate the effect of DOACs in CTEPH patients. As FXa inhibitors prevent thrombus formation by inhibiting FXa, several studies have demonstrated the measurement of AXA in atrial fibrillation or VTE patients treated with FXa inhibitors. 23–26 However, to our knowledge, this is the first study to precisely evaluate the effects of FXa inhibitors by measuring AXA in CTEPH patients. We confirmed that the peak heparin-calibrated AXA was significantly higher than the trough with all FXa inhibitors, despite differences in their dosages, namely twice daily for apixaban and once daily for rivaroxaban and edoxaban. In previous reports of CTEPH patients using DOACs, 76% of the patients received rivaroxaban, which was the most frequently used, followed by 17% using apixaban and only 1% using edoxaban. 9 In another prospective cohort study of CTEPH patients, 83% of those receiving DOACs were taking rivaroxaban. 8 Although these studies reported the results for DOACs generally, differences between the effects of each DOAC were not evident. We confirmed here that the trough heparin-calibrated AXA of apixaban was significantly higher than that of rivaroxaban or edoxaban because of the former’s twice-daily dosing ( p < .001); moreover, the peak heparin-calibrated AXA of the reduced-dose FXa inhibitor (edoxaban 30 mg/day) was significantly lower than those of the reference dose FXa inhibitors ( p = .01). These data from the present study provide fundamental knowledge for the use of FXa inhibitors in CTEPH patients. Heparin-calibrated AXA measurements should be carefully interpreted, as this method might not be sufficiently accurate for estimating plasma drug concentrations. 27 However, heparin calibrators are used commercially and are versatile, and their availability has made it possible for us, and previous studies, to compare the anticoagulant effects of different FXa inhibitors. 23,25 We also measured the plasma concentrations of rivaroxaban and apixaban to confirm the reliability of heparin-calibrated AXA, as recommended by Sabor et al. 27 In the 26 rivaroxaban-treated patients, heparin-calibrated AXA was very strongly correlated with the rivaroxaban plasma concentration ( p < .001). In addition, among the 14 patients treated with apixaban, heparin-calibrated AXA was also very strongly correlated with the apixaban plasma concentration ( p < .001). Although concern for accuracy is mentioned in previous reports 10,27 , there was still a very strong correlation with heparin-calibrated AXA for both rivaroxaban and apixaban at peak (both p < .001) and at trough (both p < .001, Supplementary Fig. 1, 2). The renal elimination of rivaroxaban, apixaban, and edoxaban has been reported as 36%, 27%, and 50% respectively. 28 Previous studies of rivaroxaban and apixaban have demonstrated that the area under the plasma concentration – time curve following a single dose significantly correlated with CCr, whereas the maximum plasma concentration did not correlated with CCr. 29,30 Although our patients were all in a steady state of anticoagulation therapy, we found that the peak heparin-calibrated AXA was only weakly negatively correlated with CCr and the trough heparin-calibrated AXA showed no significant correlation; these findings were compatible with those of the previous reports. In addition, Cirincione et al. reported that the area under the plasma concentration –time curve or the maximum plasma concentration was lower in NVAF patients treated with 2.5 mg twice daily apixaban than in those treated with 5.0 mg twice daily. 31 Although our patient numbers were very limited, we confirmed here that the peak heparin-calibrated AXA was lower in those treated with reduced-dose FXa inhibitor (edoxaban 30 mg) than with a reference dose of FXa inhibitors; this finding therefore agreed with the results of Cirincione et al. Our results suggest that we need to be cautious in considering using reduced doses of FXa inhibitors. Sakaguchi et al. 24 reported a peak heparin-calibrated AXA cutoff value of 2.19 IU/mL for major bleeding and CRNMB in NVAF patients receiving rivaroxaban. Here, we found that major bleeding and CRNMB occurred significantly in patients with a peak heparin-calibrated AXA ≥ 2.09 IU/mL, a value comparable to those in the previous study by Sakaguchi et al. Their report and our results support the concept that heparin-calibrated AXA—a widely available method—might be useful for assessing the risk of bleeding events. In previous studies, the efficacy of DOAC in CTEPH patients has been controversial. 32 Hosokawa et al. 33 reported a Japanese prospective cohort study of CTEPH patients. They reported that composite morbidity and mortality outcome was comparable between DOACs and warfarin groups, and the incidence of clinically relevant bleeding event was significantly lower in DOACs group. In contrast, Humbert et al. and Bunclark et al. 8,9 reported a higher incidence of recurrent VTE in CTEPH patients treated with DOACs than in those treated with VKAs. They hypothesized that this was because there may have been underdiagnosis of antiphospholipid syndrome or inadequate treatment adherence, partly because of the lack of a method for monitoring drug effects. In our CTEPH patients, no obvious VTEs occurred during the study period. We surmised that no recurrent thrombotic events occurred in our patients because they were still being diagnosed and followed cautiously, with detailed examinations owing to their continuing anticoagulation therapy with FXa inhibitors. This study has several limitations. First, as CTEPH is a rare disease and our study was performed in a single center, the number of participants was limited. In addition, all the participants were Japanese so the difference among the race was not confirmed. Secondly, bleeding and thrombotic events were retrospectively analyzed. Especially, we could not evaluate the relation of heparin-calibrated AXA value and recurrent VTE since no recurrent VTE event occurred in our patients. Thirdly, although we confirmed the accuracy of heparin-calibrated AXA by determining the plasma concentrations of rivaroxaban and apixaban, we could not confirm this in the cases of edoxaban because an edoxaban calibrator is not commercially available. Lastly, because this study was not performed in a prospective blinded manner, adjustment for confounders or differences among participants in the comparison of FXa inhibitors could not be totally taken into account. Furthermore, we did not compare our CTEPH patients treated with FXa inhibitors with those treated with VKAs, which is the first choice of oral anticoagulant for CTEPH patients. Nonetheless, we consider it worthwhile to have reported heparin-calibrated AXA values at both peak and trough, as this will improve understanding of the pharmacological effects in CTEPH patients treated with FXa inhibitors. Further studies are warranted, including prospective comparative studies. In conclusion, measuring heparin-calibrated AXA in CTEPH patients treated with FXa inhibitors could provide useful information, especially to predict bleeding events. Declarations Additional Information Yoshihisa Nakano reports receiving speaker and lecturer fees from Bayer, Janssen Pharmaceutical, Nippon Shinyaku, and Viatris outside the submitted work. In addition, english proofreading and article processing charges were subsidized by Adempas Post Marketing Surveillance by Bayer. Shiro Adachi reports receiving speaker and lecturer fee from Bayer, Bristol Myers Squibb, Daiichi-Sankyo, Janssen Pharmaceutical, Mochida Pharmaceutical, Nippon Shinyaku, Pfizer, and Viatris outside the submitted work. Toyoaki Murohara reports receiving speaker and lecturer fee from Bayer, Daiichi-Sankyo, and Janssen Pharmaceutical outside the submitted work. Takahisa Kondo reports receiving speaker and lecturer fee from Bayer, Bristol Myers Squibb, Daiichi-Sankyo, Janssen Pharmaceutical, Nippon Shinyaku, and Pfizer outside the submitted work. All of the other authors declare that they have no conflicts of interest to disclose. Acknowledgments We appreciate the support of the co-investigators who participated in this study. Author Contributions TM and SA were guarantors of this study. YN and TK conceived the study. YN, SA, MH, TA, IN, KY, and MY pooled the data. YN and HY analyzed the data. YN wrote the manuscript. All authors discussed the results, reviewed the manuscript, and approved the final manuscript. Data availability statement The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Ethical approval This study was approved by the Human Research Ethics Committees of Nagoya University Hospital (no. 2020-0615). References Bauersachs, R. et al. Oral Rivaroxaban for Symptomatic Venous Thromboembolism. N. Engl. J. Med. 363 , 2499–510 (2010). Büller, H. R. et al. 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Tobe, A. et al. Comparison of Anti-factor Xa Activity Among Three Different Factor Xa Inhibitors in Non-valvular Atrial Fibrillation Patients with Renal Impairment. Clin. Drug Investig. 40 , 567–573 (2020). Ono, R. et al. Impact of Renal Function on Anti-factor Xa Activity Concentrations with Edoxaban Use in Patients with Non-valvular Atrial Fibrillation. Drugs R D 22 , 281–288 (2022). Sabor, L., Raphaël, M., Dogné, J. M., Mullier, F. & Douxfils, J. Heparin-calibrated chromogenic anti-Xa assays are not suitable to assess the presence of significant direct factor Xa inhibitors levels. Thromb. Res. 156 , 36–38 (2017). Parker, K. et al. A systematic review of the efficacy and safety of anticoagulants in advanced chronic kidney disease. J. Nephrol. 35 , 2015–2033 (2022). Chang, M. et al. Effect of renal impairment on the pharmacokinetics, pharmacodynamics, and safety of apixaban. J. Clin. Pharmacol. 56 , 637–645 (2016). Kubitza, D. et al. Effects of renal impairment on the pharmacokinetics, pharmacodynamics and safety of rivaroxaban, an oral, direct Factor Xa inhibitor. Br. J. Clin. Pharmacol. 70 , 703–712 (2010). Cirincione, B. et al. Population Pharmacokinetics of Apixaban in Subjects With Nonvalvular Atrial Fibrillation. CPT Pharmacometrics Syst. Pharmacol. 7 , 728–738 (2018). Porres-Aguilar, M. et al. Direct oral anticoagulants in chronic thromboembolic pulmonary hypertension. J. Thromb. Thrombolysis 52 , 791–796 (2021). Hosokawa, K. et al. Long-term outcome of chronic thromboembolic pulmonary hypertension using direct oral anticoagulants and warfarin: a Japanese prospective cohort study. J. Thromb. Haemost. S1538-7836(23)00270–2 (2023) doi:10.1016/j.jtha.2023.03.036. Additional Declarations Competing interest reported. Yoshihisa Nakano reports receiving speaker and lecturer fees from Bayer, Janssen Pharmaceutical, Nippon Shinyaku, and Viatris outside the submitted work. In addition, english proofreading and article processing charges were subsidized by Adempas Post Marketing Surveillance by Bayer. Shiro Adachi reports receiving speaker and lecturer fee from Bayer, Bristol Myers Squibb, Daiichi-Sankyo, Janssen Pharmaceutical, Mochida Pharmaceutical, Nippon Shinyaku, Pfizer, and Viatris outside the submitted work. Toyoaki Murohara reports receiving speaker and lecturer fee from Bayer, Daiichi-Sankyo, and Janssen Pharmaceutical outside the submitted work. Takahisa Kondo reports receiving speaker and lecturer fee from Bayer, Bristol Myers Squibb, Daiichi-Sankyo, Janssen Pharmaceutical, Nippon Shinyaku, and Pfizer outside the submitted work. All of the other authors declare that they have no conflicts of interest to disclose. 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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-4893570","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":352990398,"identity":"08bd2f4b-45b5-49b5-aaf6-74b84a6ddd05","order_by":0,"name":"Yoshihisa Nakano","email":"","orcid":"","institution":"Nagoya University Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yoshihisa","middleName":"","lastName":"Nakano","suffix":""},{"id":352990399,"identity":"e9d9afac-51b5-42df-a438-417fe3be60e3","order_by":1,"name":"Shiro Adachi","email":"data:image/png;base64,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","orcid":"","institution":"Nagoya University Hospital","correspondingAuthor":true,"prefix":"","firstName":"Shiro","middleName":"","lastName":"Adachi","suffix":""},{"id":352990400,"identity":"cc12f6f9-294a-4b70-b61b-3d9434ec97ac","order_by":2,"name":"Miku Hirose","email":"","orcid":"","institution":"Nagoya University Graduate School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Miku","middleName":"","lastName":"Hirose","suffix":""},{"id":352990403,"identity":"fce25314-4337-419a-ac51-30d98b4051ef","order_by":3,"name":"Takeshi Adachi","email":"","orcid":"","institution":"Nagoya University Graduate School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Takeshi","middleName":"","lastName":"Adachi","suffix":""},{"id":352990405,"identity":"0e358021-5e32-4be8-a232-aac99dbaca4b","order_by":4,"name":"Itsumure Nishiyama","email":"","orcid":"","institution":"Nagoya University Graduate School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Itsumure","middleName":"","lastName":"Nishiyama","suffix":""},{"id":352990408,"identity":"191f7bbd-ae90-429e-a2ee-7ffe2532ec7e","order_by":5,"name":"Kenichiro Yasuda","email":"","orcid":"","institution":"Nihon Sekijujisha Aichi Iryo Center Nagoya Daiichi Byoin","correspondingAuthor":false,"prefix":"","firstName":"Kenichiro","middleName":"","lastName":"Yasuda","suffix":""},{"id":352990409,"identity":"23a4295c-8f40-4398-8419-66810966eb93","order_by":6,"name":"Masahiro Yoshida","email":"","orcid":"","institution":"Meijyo Hospital","correspondingAuthor":false,"prefix":"","firstName":"Masahiro","middleName":"","lastName":"Yoshida","suffix":""},{"id":352990410,"identity":"655adb11-c15d-4ce8-82fc-0bd276a2ed7a","order_by":7,"name":"Takahisa Kondo","email":"","orcid":"","institution":"Nagoya Medical Center","correspondingAuthor":false,"prefix":"","firstName":"Takahisa","middleName":"","lastName":"Kondo","suffix":""},{"id":352990411,"identity":"f39540d7-199f-4a1a-ae63-6f8a64718bba","order_by":8,"name":"Toyoaki Murohara","email":"","orcid":"","institution":"Nagoya University Graduate School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Toyoaki","middleName":"","lastName":"Murohara","suffix":""}],"badges":[],"createdAt":"2024-08-11 03:23:28","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4893570/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4893570/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-024-74481-7","type":"published","date":"2024-10-28T16:05:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":66632956,"identity":"1fbbd075-4314-4fdf-b3b0-e2e1598afa4d","added_by":"auto","created_at":"2024-10-15 05:02:04","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":760479,"visible":true,"origin":"","legend":"\u003cp\u003eStudy flow chart of the patients enrolled. CTEPH, chronic thromboembolic pulmonary hypertension.\u003c/p\u003e","description":"","filename":"Figure1SientificReports.png","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/2ea43c9e2528ca0af25b574d.png"},{"id":66632955,"identity":"b344254b-28ee-45bc-bac1-52e2faf7a1f9","added_by":"auto","created_at":"2024-10-15 05:02:04","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2013986,"visible":true,"origin":"","legend":"\u003cp\u003eHeparin-calibrated anti-factor Xa activity in all 50 patients. a) Comparison between trough and peak. b) Comparison between rivaroxaban, apixaban, and edoxaban at trough and peak. c) Comparison between reduced-dose factor Xa inhibitor and reference-dose factor Xa inhibitor. AXA, anti-factor Xa activity.\u003c/p\u003e","description":"","filename":"Figure2SientificReports.png","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/2ef2548caecc0137264e5a19.png"},{"id":66632964,"identity":"73963941-2fd9-4ed1-a26d-5ea6355a0692","added_by":"auto","created_at":"2024-10-15 05:02:05","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1236332,"visible":true,"origin":"","legend":"\u003cp\u003ea) Plasma concentration of rivaroxaban at peak and trough. b) Correlation of heparin-calibrated anti-factor Xa activity and plasma concentration of rivaroxaban. AXA, anti-factor Xa activity.\u003c/p\u003e","description":"","filename":"Figure3SientificReports.png","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/503ee938a7800548d720cadf.png"},{"id":66632957,"identity":"9fdb3974-9a33-48db-a86b-a4f8914eb9ea","added_by":"auto","created_at":"2024-10-15 05:02:04","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":922792,"visible":true,"origin":"","legend":"\u003cp\u003ea) Plasma concentration of apixaban at peak and trough. b) Correlation of heparin-calibrated anti-factor Xa activity and plasma concentration of apixaban. AXA, anti-factor Xa activity.\u003c/p\u003e","description":"","filename":"Figure4SientificReports.png","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/021655d6c79c5a351bc282ff.png"},{"id":66634794,"identity":"c8fffd67-5365-420d-ab32-1e2740beff4c","added_by":"auto","created_at":"2024-10-15 05:10:04","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":749361,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation of creatinine clearance and heparin-calibrated anti-factor Xa activity: a) at peak for all factor Xa inhibitors; b) at trough of once-daily factor Xa inhibitor; c) at trough of twice-daily factor Xa­­­ inhibitor. AXA, anti-factor Xa activity; BID, twice daily; CCr, creatinine clearance; QD, once daily.\u003c/p\u003e","description":"","filename":"Figure5SientificReports.png","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/989d5cb71d16e8ccf7fbdd68.png"},{"id":66632960,"identity":"149a546f-aa5d-4b44-b204-4ec8c36fba09","added_by":"auto","created_at":"2024-10-15 05:02:04","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1029571,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between heparin-calibrated anti-factor Xa activity and bleeding events: a) receiver-operating characteristic curve analysis for major and non-major clinically relevant bleeding events using peak heparin-calibrated anti-factor Xa activity, b) Kaplan-Meier analysis of major and non-major clinically relevant bleeding events. AUC, area under curve; AXA, anti-factor Xa activity; CI, confidence intervals; HR, hazard ratio; ROC, receiver operating characteristic.\u003c/p\u003e\n\u003cp\u003e*: Multi-variate cox proportional-hazards model adjusted by age and presence of invasive treatment.\u003c/p\u003e","description":"","filename":"Figure6SientificReports.png","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/72ea8154e163d61b418b89fd.png"},{"id":68206742,"identity":"679d38a0-fe6e-4217-9366-fc08171f035a","added_by":"auto","created_at":"2024-11-04 16:33:22","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7384421,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/5a61adae-9322-402c-8ad5-2a5d022dee94.pdf"},{"id":66632959,"identity":"a5515b6a-f590-49a0-8a1e-5e744e846f15","added_by":"auto","created_at":"2024-10-15 05:02:04","extension":"docx","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":14008,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformationScientificReports.docx","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/4dea386e39a7d832231b9b8d.docx"},{"id":66632961,"identity":"cea13d1e-8a6f-4a39-8770-d649cc298a4d","added_by":"auto","created_at":"2024-10-15 05:02:04","extension":"tif","order_by":9,"title":"","display":"","copyAsset":false,"role":"supplement","size":2315266,"visible":true,"origin":"","legend":"","description":"","filename":"SupplemetaryFigure1.tif","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/347fc4317c93a249ab200211.tif"},{"id":66632962,"identity":"a2f7bf17-f575-402e-8f0d-6d36283f5291","added_by":"auto","created_at":"2024-10-15 05:02:04","extension":"tif","order_by":10,"title":"","display":"","copyAsset":false,"role":"supplement","size":2238938,"visible":true,"origin":"","legend":"","description":"","filename":"SupplemetaryFigure2.tif","url":"https://assets-eu.researchsquare.com/files/rs-4893570/v1/087df06d2f1bf51ef2945445.tif"}],"financialInterests":"Competing interest reported. Yoshihisa Nakano reports receiving speaker and lecturer fees from Bayer, Janssen Pharmaceutical, Nippon Shinyaku, and Viatris outside the submitted work. In addition, english proofreading and article processing charges were subsidized by Adempas Post Marketing Surveillance by Bayer. Shiro Adachi reports receiving speaker and lecturer fee from Bayer, Bristol Myers Squibb, Daiichi-Sankyo, Janssen Pharmaceutical, Mochida Pharmaceutical, Nippon Shinyaku, Pfizer, and Viatris outside the submitted work. Toyoaki Murohara reports receiving speaker and lecturer fee from Bayer, Daiichi-Sankyo, and Janssen Pharmaceutical outside the submitted work. Takahisa Kondo reports receiving speaker and lecturer fee from Bayer, Bristol Myers Squibb, Daiichi-Sankyo, Janssen Pharmaceutical, Nippon Shinyaku, and Pfizer outside the submitted work. All of the other authors declare that they have no conflicts of interest to disclose.","formattedTitle":"Monitoring anti-factor Xa activity in patients with chronic thromboembolic pulmonary hypertension treated with factor Xa inhibitors","fulltext":[{"header":"Introduction","content":"\u003cp\u003eChronic thromboembolic pulmonary hypertension (CTEPH) is characterized by persistent organized thrombi of the pulmonary artery and pulmonary hypertension. Therefore, lifelong anticoagulation therapy is indispensable for CTEPH patients. For a period of years, vitamin-K antagonists (VKAs)\u0026mdash;mostly warfarin\u0026mdash;were the only oral anticoagulants available. Nowadays, the efficacy and safety of direct oral anticoagulants (DOACs) in patients with non-valvular atrial fibrillation (NVAF) or acute venous thromboembolism (VTE) have proven to be non-inferior, or superior, to VKAs.\u003csup\u003e1\u0026ndash;6\u003c/sup\u003e However, data on the efficacy and safety of DOACs in CTEPH patients remain limited. KABUKI Trial was the first randomized phase Ⅲ trial that reported the non-inferiority of edoxaban to warfarin in CTEPH patients, although further large-scale multinational long-term study is warranted.\u003csup\u003e7\u003c/sup\u003e In contrast, a UK retrospective study reported that the efficacy and safety of DOACs were comparable to those of VKAs in operable CTEPH patients.\u003csup\u003e9\u003c/sup\u003e Furthermore, although laboratory monitoring of DOACs is basically unnecessary, it is essential to objectively evaluate these drugs\u0026rsquo; actions in any investigation of their efficacy and safety. Previous studies have recommended measuring plasma drug concentrations to monitor DOAC effects, and anti-factor Xa activity (AXA) has also been reported as a convenient method of monitoring factor Xa (FXa) inhibitors.\u003csup\u003e10\u0026ndash;13\u003c/sup\u003e Therefore, here, we aimed to evaluate the pharmacological effects of FXa inhibitors by measuring heparin-calibrated AXA in patients with CTEPH. In addition, we also aimed to assess the relation of heparin-calibrated AXA value and risk of clinical events.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy population\u003c/h2\u003e \u003cp\u003eThis was a single-center observational study. We screened 164 Japanese patients who were diagnosed with, and treated for, CTEPH at our institution from 2010 to 2021 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The patients were treated with the VKA warfarin or with the FXa inhibitors rivaroxaban, apixaban, or edoxaban. Among those treated with FXa inhibitors, we enrolled 50 consecutive patients who visited our hospital for detailed examination from April 2021 to December 2021. All 50 patients provided written informed consent. This study was conducted in accordance with the Declaration of Helsinki and the ethical standards of the institutional committee on human experimentation, and it was approved by the Human Research Ethics Committees of Nagoya University Hospital (no. 2020\u0026thinsp;\u0026minus;\u0026thinsp;0615).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eDefinition\u003c/h2\u003e \u003cp\u003eChronic pulmonary thrombi or chronic perfusion obstruction was confirmed by either enhanced computed tomography or perfusion scan after at least 3 months of effective anticoagulation. Pulmonary hypertension was defined as mean pulmonary arterial pressure (PAP)\u0026thinsp;\u0026ge;\u0026thinsp;25 mmHg and pulmonary arterial wedge pressure (PAWP)\u0026thinsp;\u0026le;\u0026thinsp;15 mmHg according to the 2015 European Society of Cardiology/ European Respiratory Society guidelines for the diagnosis and treatment of pulmonary hypertension.\u003csup\u003e14\u003c/sup\u003e Thus, CTEPH was diagnosed when patients met the conditions of both chronic pulmonary thrombi and pulmonary hypertension.\u003c/p\u003e \u003cp\u003eRight heart catheterization was performed within median 3 days before or after blood collection. PAWP, PAP, right ventricular pressure, and right atrial pressure were measured. Cardiac output was calculated by using the Fick method, and pulmonary vascular resistance (PVR) was calculated by using the standard formula: PVR = (mean PAP\u0026thinsp;\u0026minus;\u0026thinsp;mean PAWP)/cardiac output.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eAnticoagulants and measurement of coagulation function\u003c/h2\u003e \u003cp\u003eThe FXa inhibitor used was selected according to the decision of each attending physician. The dosage was decided according to the description of the Japan Pharmaceutical Reference, namely 15 mg once per day for rivaroxaban, 5 mg twice per day for apixaban, and 60 mg or 30 mg once per day for edoxaban.\u003c/p\u003e \u003cp\u003eAll patients had received continuous anticoagulation therapy with the same drug at least 30 days before heparin-calibrated AXA measurement. Heparin-calibrated AXA, prothrombin time, and activated partial thromboplastin time were examined twice: at trough and peak. In accordance with previous reports, we defined the trough time as immediately before the administration of any FXa inhibitor.\u003csup\u003e12,13\u003c/sup\u003e We defined the peak time as 2 h after drug administration in patients taking edoxaban and 3 h after in those taking rivaroxaban or apixaban.\u003csup\u003e12,13\u003c/sup\u003e To ensure that blood was collected accurately at the trough and peak times, we collected it by using the following procedure: outpatients brought their anticoagulant drug to the outpatient clinic instead of taking it at home and took the tablet at the clinic just after their first blood collection; in the case of inpatients, ward staff managed the time of intake.\u003c/p\u003e \u003cp\u003eBlood samples were centrifuged at 3000\u003cem\u003eg\u003c/em\u003e for 5 min, and platelet-poor plasma was frozen at \u0026minus;\u0026thinsp;80\u0026deg;C until the AXA analysis was performed. AXA was measured with a HemosIL Liquid Heparin Kit (Instrumentation Laboratory, Lexington, KY, USA) and HemosIL Heparin Calibrators on an ACL TOP hemostasis test system (Werfen, Bedford, MA, USA). This test is a one-stage assay consisting of incubation of a diluted plasma sample with a substrate of FXa to measure the optical density at a wavelength of 405 nm after the addition of bovine FXa. The optical density is measured on the ACL TOP instrument. At the same time, we measured the plasma concentration of apixaban with HemosIL Apixaban Calibrators and that of rivaroxaban with HemosIL Rivaroxaban Calibrators, respectively (Instrumentation Laboratory).\u003csup\u003e15\u003c/sup\u003e Since there were no edoxaban calibrator that was commercially available, we could not confirm the plasma concentration of edoxaban.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eRetrospective analysis\u003c/h2\u003e \u003cp\u003eThe medical records of all 50 patients from the time of initiation of the FXa inhibitor to the day of heparin-calibrated AXA measurement were retrospectively reviewed. Recurrent VTE was defined as newly diagnosed of either deep vein thrombosis, pulmonary embolism, or as an exacerbation CTEPH, or any combination of these, with or without symptoms, as confirmed by the detection of new or exacerbated thrombus on imaging examination. Major bleeding and clinically relevant non-major bleeding (CRNMB) were defined according to the criteria of the International Society on Thrombosis and Haemostasis.\u003csup\u003e16\u0026ndash;18\u003c/sup\u003e Major bleeding was diagnosed when at least one of the following criteria was met: bleeding associated with a\u0026thinsp;\u0026ge;\u0026thinsp;2 g/dL decrease in hemoglobin level, bleeding leading to \u0026ge;\u0026thinsp;2 units of blood transfusion, symptomatic bleeding in a critical area or organ, or fatal bleeding. CRNMB was diagnosed as clinically overt bleeding that did not meet the criteria for major bleeding but that required medical intervention, hospitalization, increased level of care, or face-to-face evaluation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eContinuous data are presented as medians and interquartile ranges, and categorical data are presented as numbers and percentages. Data of heparin-calibrated AXA were presented as median and 5th to 95th percentiles (with the exception of three cases, in which the 25th to 75th percentiles and 10th to 90th percentiles were used because of the limited numbers of participants; see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Continuous data were compared between two groups by using the Mann\u0026ndash;Whitney \u003cem\u003eU\u003c/em\u003e-test, or among three or more groups by using the Kruskal\u0026ndash;Wallis test. The post-hoc analysis was adjusted for Bonferroni correction. Categorical data were compared by using the chi-square test or Fisher\u0026rsquo;s exact test, depending on the distribution of the data. Correlation analysis was performed by using Spearman\u0026rsquo;s rank correlation owing to the distribution of the data. A receiver operating characteristic (ROC) analysis was used to determine the cutoff value of the peak heparin-calibrated AXA level as a predictor of bleeding events. The cutoff value was determined as the point on the ROC curve closest to (0,1).\u003csup\u003e19\u003c/sup\u003e The Kaplan\u0026ndash;Meier method was used to estimate cumulated bleeding rates, and differences between groups were evaluated by using the log-rank method. Multi-variate cox proportional-hazards model adjusted by age and presence of invasive treatment was performed to determine the hazard ratio (HR) and 95% confidence intervals (CI) of bleeding events between two groups. A \u003cem\u003ep\u003c/em\u003e-value of \u0026lt;\u0026thinsp;.05 was considered statistically significant. Statistical analyses were conducted by using Stata version 17 (Stata Corp, College Station, Texas, USA) and the SPSS statistical software program (version 27.0 for Windows; SPSS, Chicago, IL, USA).\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 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of the 50 patients at baseline\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge, years\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e63\u0026thinsp;\u0026plusmn;\u0026thinsp;14\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21 (42)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBody weight, kg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62.1\u0026thinsp;\u0026plusmn;\u0026thinsp;15.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBody surface area, m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHistory of definitively diagnosed acute pulmonary embolism, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25 (50)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHistory of deep vein thrombosis, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23 (46)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActive cancer \u003csup\u003ea\u003c/sup\u003e, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 (4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThrombophilia, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1 (2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCardiovascular disease, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 (4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChronic lung disease, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9 (18)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eType of CTEPH at diagnosis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCentral CTEPH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13 (26)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePeripheral CTEPH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e37 (74)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInvasive treatment, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePulmonary endarterectomy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7 (14)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBalloon pulmonary angioplasty\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29 (58)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUse of oral pulmonary vasodilator (riociguat), n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e32 (64)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWHO functional class (1/2/3/4), n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4/39/7/0 (8/78/14/0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLaboratory parameters\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCreatinine clearance S\u003csup\u003eb\u003c/sup\u003e, mL/min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e68.0 (54.4\u0026ndash;104.9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHemoglobin, g/dL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlatelets, \u0026times;10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27.8\u0026thinsp;\u0026plusmn;\u0026thinsp;11.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eD-dimer, \u0026micro;g/mL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFibrin monomer complex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.35\u0026thinsp;\u0026plusmn;\u0026thinsp;1.74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThrombin antithrombin complex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.9 (0.6\u0026ndash;1.4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProthrombin fragment 1\u0026thinsp;+\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e147.5 (111.3\u0026ndash;184.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTroponin T, ng/mL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.007 (0.005\u0026ndash;0.012)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBNP, pg/mL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9.7 (5.8\u0026ndash;26.7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEchocardiography\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLVDd, mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e42.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.1\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\u003e68.0\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTRPG, mmHg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e39.0 (28.8\u0026ndash;54.9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTAPSE, mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17.8\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHemodynamics\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean PAP, mmHg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30\u0026thinsp;\u0026plusmn;\u0026thinsp;11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRAP, mmHg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCI, L/min/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePVR, Wood units\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.0 (3.3\u0026ndash;8.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnticoagulant used, n (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEdoxaban\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10 (20)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eApixaban\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14 (28)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRivaroxaban\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26 (52)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003eBNP, brain natriuretic peptide; CI, cardiac index; LVDd, left ventricular end-diastolic diameter; LVEF, left ventricular ejection fraction; PAP, pulmonary arterial pressure; PVR, pulmonary vascular resistance; RAP, right atrial pressure; TAPSE, tricuspid annular plane systolic excursion; TRPG, tricuspid regurgitation pressure gradient\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003eCategorical variables are presented as numbers and percentages, and continuous variables are presented as means\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation or medians and interquartile range.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e\u003csup\u003ea\u003c/sup\u003e Active cancer was defined as any cancer, including locally recurrent, regionally advanced, or metastatic cancer, that had been diagnosed or treated in the 6 months before the enrollment\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e\u003csup\u003eb\u003c/sup\u003e Creatinine clearance was calculated by using the Cockcroft\u0026ndash;Gault equation.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e\u003csup\u003ec\u003c/sup\u003e echocardiography was performed in limited participants (n\u0026thinsp;=\u0026thinsp;39) nearly before or after heparin-calibrated AXA measurement.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\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 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCoagulation markers at trough and peak\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=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTrough\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePeak\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProthrombin time, s\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActivated partial thromboplastin time, s\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37.5\u0026thinsp;\u0026plusmn;\u0026thinsp;6.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeparin-calibrated AXA in all patients, IU/mL \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.14 (0.02\u0026ndash;1.54)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.90 (0.84\u0026ndash;3.07)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeparin-calibrated AXA for rivaroxaban, IU/mL \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.11 (0.05\u0026ndash;0.50)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.98 (0.89\u0026ndash;3.08)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeparin-calibrated AXA for edoxaban, IU/mL \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.11 (0.01\u0026ndash;0.30) \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.59 (0.46\u0026ndash;2.43) \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e.005\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeparin-calibrated AXA for apixaban, IU/mL \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.70 (0.23\u0026ndash;1.92) \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.04 (1.16\u0026ndash;3.86) \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeparin-calibrated AXA for once daily FXa inhibitors, IU/mL \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.11 (0.01\u0026ndash;0.36)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.87 (0.76\u0026ndash;3.06)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeparin-calibrated AXA for reference dose of FXa inhibitor, IU/mL \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.14 (0.02\u0026ndash;1.67)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.95 (0.91\u0026ndash;3.09)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeparin-calibrated AXA for reduced dose of FXa inhibitor, IU/mL \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.11 (0.07\u0026ndash;0.23) \u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.25 (0.77\u0026ndash;1.70) \u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eApixaban plasma concentration \u003csup\u003ec\u003c/sup\u003e, ng/mL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e116.2 (58.8\u0026ndash;362.1) \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e273.2 (181.7\u0026ndash;564.8) \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRivaroxaban plasma concentration \u003csup\u003ed\u003c/sup\u003e, ng/mL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15.4 (2.2\u0026ndash;69.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e216.2 (119.2\u0026ndash;457.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eAXA, anti-factor Xa activity; FXa, factor Xa.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eNumbers are described as means\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation, or medians (5th to 95th percentiles).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003csup\u003ea\u003c/sup\u003e Heparin-calibrated AXA was measured in all 50 patients: 26 on rivaroxaban, 14 on apixaban, and 10 on edoxaban. Once-daily factor-Xa inhibitor included was rivaroxaban or edoxaban (n\u0026thinsp;=\u0026thinsp;36).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003csup\u003eb\u003c/sup\u003e Reference dose represented rivaroxaban 15 mg/day, apixaban 10 mg/day, or edoxaban 60 mg/day (n\u0026thinsp;=\u0026thinsp;45). Reduced dose represented edoxaban 30 mg/day (n\u0026thinsp;=\u0026thinsp;5).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003csup\u003ec\u003c/sup\u003e Apixaban drug concentration was measured in 14 patients taking apixaban.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003csup\u003ed\u003c/sup\u003e Rivaroxaban drug concentration was measured in 26 patients taking rivaroxaban.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003csup\u003ee\u003c/sup\u003e As the number of participants was limited, the 10th and 90th percentiles are described.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003csup\u003ef\u003c/sup\u003e As the number of participants was limited, the 25th and 75th percentiles are described.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eThe mean age of the 50 patients evaluated was 63\u0026thinsp;\u0026plusmn;\u0026thinsp;14 years, and 42% were male (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A history of VTE (pulmonary embolism plus deep vein thrombosis, deep vein thrombosis alone, or pulmonary embolism alone) was reported by 66% of patients, and 50% of patients had a history of acute pulmonary embolism. Along with anticoagulation therapy, a pulmonary vasodilator (riociguat) was used in 64% of patients, and invasive treatment (pulmonary endarterectomy [PEA] or balloon pulmonary angioplasty [BPA], or both) was performed in 70% of patients (including one who underwent both procedures) at the time of AXA measurement. The serum D-dimer level was 1.0 \u0026micro;g/mL or lower in all patients, suggesting that none of them was in a hypercoagulability state.\u003c/p\u003e \u003cp\u003eThe median heparin-calibrated AXA across all 50 patients was significantly higher at peak (1.90 IU/mL) than at trough (0.14 IU/mL, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). We then compared the heparin-calibrated AXA values between pairs of FXa inhibitors. The trough heparin-calibrated AXA was significantly higher in patients treated with apixaban than in those given rivaroxaban or edoxaban (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, p\u0026thinsp;\u0026lt;\u0026thinsp;.001). In contrast, the peak heparin-calibrated AXA values were comparable among the three groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, p\u0026thinsp;=\u0026thinsp;.09). In addition, when we defined edoxaban 30 mg/day as a reduced dose and all the other doses (edoxaban 60 mg/day, apixaban 10 mg/day, and rivaroxaban 15 mg/day) as the reference dose, the peak heparin-calibrated AXA was significantly lower in the reduced-dose group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.01, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAmong the 26 patients treated with rivaroxaban, the plasma concentration of the drug was significantly higher at peak (median 216.2 ng/mL) than at trough (median 15.4 ng/mL, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). To confirm the accuracy of the heparin-calibrated AXA, we analyzed its relationship with the plasma rivaroxaban concentration. The two sets of data were very strongly correlated (\u003cem\u003eR\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.957, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Among the 14 patients treated with apixaban, the plasma concentration of the drug was significantly higher at peak (median 273.2 ng/mL) than at trough (median 116.2 ng/mL, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). The heparin-calibrated AXA value and the plasma concentration of apixaban were very strongly correlated (\u003cem\u003eR\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.980, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). Furthermore, we confirmed the correlation between heparin-calibrated AXA and plasma concentration separately at trough and peak for each drug; we found strong correlations in the cases of both rivaroxaban and apixaban (Supplementary Figs.\u0026nbsp;1, 2: all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWe then analyzed the relationship between renal function and heparin-calibrated AXA (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Peak heparin-calibrated AXA and creatinine clearance (CCr) were significantly negatively correlated (\u003cem\u003eR\u003c/em\u003e = \u0026ndash;.314, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.03) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), whereas there was no correlation between CCr and heparin-calibrated AXA at trough in the case of the once-daily anticoagulants (rivaroxaban and edoxaban, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.19; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb) or the twice daily anticoagulant (apixaban, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.08; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAmong the 50 patients, no recurrent VTE occurred, major bleeding events occurred in four, and CRNMB occurred in three during the observational period of median 787 (Interquartile range, 487\u0026ndash;1334) days. We performed an ROC analysis to determine the cutoff points of the peak heparin-calibrated AXA level for bleeding events, for which the area under curve was 0.79 (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The sensitivity and specificity of the cutoff point of a peak heparin-calibrated AXA of 2.09 IU/mL were 86% and 72%, respectively. We then used this cutoff point to perform a Kaplan\u0026ndash;Meier analysis of major bleeding and CRNMB events. The cumulative rate of major bleeding and CRNMB adjusted by age and presence of invasive treatment was significantly higher in patients with peak heparin-calibrated AXA\u0026thinsp;\u0026ge;\u0026thinsp;2.09 IU/mL than in patients with values below this point (HR 11.5 [95% CI: 1.3\u0026ndash;105.2], Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eWe report four main findings from this study of CTEPH patients. First, peak heparin-calibrated AXA was significantly higher than trough with all three FXa inhibitors, and the trough heparin-calibrated AXA of apixaban was significantly higher than that of rivaroxaban or edoxaban, reflecting the twice-daily dosing of apixaban. Secondly, peak heparin-calibrated AXA was significantly lower with the reduced-dose FXa inhibitor than with the reference dose. Thirdly, heparin-calibrated AXA was very strongly correlated with the plasma concentrations of rivaroxaban and apixaban. Lastly, major bleeding and CRNMB occurred significantly in patients with peak heparin-calibrated AXA\u0026thinsp;\u0026ge;\u0026thinsp;2.09 IU/mL.\u003c/p\u003e \u003cp\u003eIn recent years, DOACs have proven to be at least non-inferior to VKAs in patients with VTE.\u003csup\u003e1\u0026ndash;3\u003c/sup\u003e However, DOACs are contraindicated in patients with mechanical heart valves or with anti-phospholipid syndrome.\u003csup\u003e20\u0026ndash;22\u003c/sup\u003e In patients with CTEPH, lifelong anticoagulation with sufficient effect is the most fundamental and important treatment, as these patients are at high risk of the clinical condition of VTE. Therefore, although DOACs are used in CTEPH patients worldwide for secondary prevention of VTE (despite their still not being strictly recommended for use in these patients), we need to carefully validate the effect of DOACs in CTEPH patients. As FXa inhibitors prevent thrombus formation by inhibiting FXa, several studies have demonstrated the measurement of AXA in atrial fibrillation or VTE patients treated with FXa inhibitors.\u003csup\u003e23\u0026ndash;26\u003c/sup\u003e However, to our knowledge, this is the first study to precisely evaluate the effects of FXa inhibitors by measuring AXA in CTEPH patients. We confirmed that the peak heparin-calibrated AXA was significantly higher than the trough with all FXa inhibitors, despite differences in their dosages, namely twice daily for apixaban and once daily for rivaroxaban and edoxaban.\u003c/p\u003e \u003cp\u003eIn previous reports of CTEPH patients using DOACs, 76% of the patients received rivaroxaban, which was the most frequently used, followed by 17% using apixaban and only 1% using edoxaban.\u003csup\u003e9\u003c/sup\u003e In another prospective cohort study of CTEPH patients, 83% of those receiving DOACs were taking rivaroxaban.\u003csup\u003e8\u003c/sup\u003e Although these studies reported the results for DOACs generally, differences between the effects of each DOAC were not evident. We confirmed here that the trough heparin-calibrated AXA of apixaban was significantly higher than that of rivaroxaban or edoxaban because of the former\u0026rsquo;s twice-daily dosing (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001); moreover, the peak heparin-calibrated AXA of the reduced-dose FXa inhibitor (edoxaban 30 mg/day) was significantly lower than those of the reference dose FXa inhibitors (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.01). These data from the present study provide fundamental knowledge for the use of FXa inhibitors in CTEPH patients.\u003c/p\u003e \u003cp\u003eHeparin-calibrated AXA measurements should be carefully interpreted, as this method might not be sufficiently accurate for estimating plasma drug concentrations.\u003csup\u003e27\u003c/sup\u003e However, heparin calibrators are used commercially and are versatile, and their availability has made it possible for us, and previous studies, to compare the anticoagulant effects of different FXa inhibitors.\u003csup\u003e23,25\u003c/sup\u003e We also measured the plasma concentrations of rivaroxaban and apixaban to confirm the reliability of heparin-calibrated AXA, as recommended by Sabor et al.\u003csup\u003e27\u003c/sup\u003e In the 26 rivaroxaban-treated patients, heparin-calibrated AXA was very strongly correlated with the rivaroxaban plasma concentration (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001). In addition, among the 14 patients treated with apixaban, heparin-calibrated AXA was also very strongly correlated with the apixaban plasma concentration (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001). Although concern for accuracy is mentioned in previous reports\u003csup\u003e10,27\u003c/sup\u003e, there was still a very strong correlation with heparin-calibrated AXA for both rivaroxaban and apixaban at peak (both \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001) and at trough (both \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.001, Supplementary Fig.\u0026nbsp;1, 2).\u003c/p\u003e \u003cp\u003eThe renal elimination of rivaroxaban, apixaban, and edoxaban has been reported as 36%, 27%, and 50% respectively.\u003csup\u003e28\u003c/sup\u003e Previous studies of rivaroxaban and apixaban have demonstrated that the area under the plasma concentration \u0026ndash; time curve following a single dose significantly correlated with CCr, whereas the maximum plasma concentration did not correlated with CCr.\u003csup\u003e29,30\u003c/sup\u003e Although our patients were all in a steady state of anticoagulation therapy, we found that the peak heparin-calibrated AXA was only weakly negatively correlated with CCr and the trough heparin-calibrated AXA showed no significant correlation; these findings were compatible with those of the previous reports. In addition, Cirincione et al. reported that the area under the plasma concentration \u0026ndash;time curve or the maximum plasma concentration was lower in NVAF patients treated with 2.5 mg twice daily apixaban than in those treated with 5.0 mg twice daily.\u003csup\u003e31\u003c/sup\u003e Although our patient numbers were very limited, we confirmed here that the peak heparin-calibrated AXA was lower in those treated with reduced-dose FXa inhibitor (edoxaban 30 mg) than with a reference dose of FXa inhibitors; this finding therefore agreed with the results of Cirincione et al. Our results suggest that we need to be cautious in considering using reduced doses of FXa inhibitors.\u003c/p\u003e \u003cp\u003eSakaguchi et al.\u003csup\u003e24\u003c/sup\u003e reported a peak heparin-calibrated AXA cutoff value of 2.19 IU/mL for major bleeding and CRNMB in NVAF patients receiving rivaroxaban. Here, we found that major bleeding and CRNMB occurred significantly in patients with a peak heparin-calibrated AXA\u0026thinsp;\u0026ge;\u0026thinsp;2.09 IU/mL, a value comparable to those in the previous study by Sakaguchi et al. Their report and our results support the concept that heparin-calibrated AXA\u0026mdash;a widely available method\u0026mdash;might be useful for assessing the risk of bleeding events.\u003c/p\u003e \u003cp\u003eIn previous studies, the efficacy of DOAC in CTEPH patients has been controversial.\u003csup\u003e32\u003c/sup\u003e Hosokawa et al.\u003csup\u003e33\u003c/sup\u003e reported a Japanese prospective cohort study of CTEPH patients. They reported that composite morbidity and mortality outcome was comparable between DOACs and warfarin groups, and the incidence of clinically relevant bleeding event was significantly lower in DOACs group. In contrast, Humbert et al. and Bunclark et al.\u003csup\u003e8,9\u003c/sup\u003e reported a higher incidence of recurrent VTE in CTEPH patients treated with DOACs than in those treated with VKAs. They hypothesized that this was because there may have been underdiagnosis of antiphospholipid syndrome or inadequate treatment adherence, partly because of the lack of a method for monitoring drug effects. In our CTEPH patients, no obvious VTEs occurred during the study period. We surmised that no recurrent thrombotic events occurred in our patients because they were still being diagnosed and followed cautiously, with detailed examinations owing to their continuing anticoagulation therapy with FXa inhibitors.\u003c/p\u003e \u003cp\u003eThis study has several limitations. First, as CTEPH is a rare disease and our study was performed in a single center, the number of participants was limited. In addition, all the participants were Japanese so the difference among the race was not confirmed. Secondly, bleeding and thrombotic events were retrospectively analyzed. Especially, we could not evaluate the relation of heparin-calibrated AXA value and recurrent VTE since no recurrent VTE event occurred in our patients. Thirdly, although we confirmed the accuracy of heparin-calibrated AXA by determining the plasma concentrations of rivaroxaban and apixaban, we could not confirm this in the cases of edoxaban because an edoxaban calibrator is not commercially available. Lastly, because this study was not performed in a prospective blinded manner, adjustment for confounders or differences among participants in the comparison of FXa inhibitors could not be totally taken into account. Furthermore, we did not compare our CTEPH patients treated with FXa inhibitors with those treated with VKAs, which is the first choice of oral anticoagulant for CTEPH patients. Nonetheless, we consider it worthwhile to have reported heparin-calibrated AXA values at both peak and trough, as this will improve understanding of the pharmacological effects in CTEPH patients treated with FXa inhibitors. Further studies are warranted, including prospective comparative studies.\u003c/p\u003e \u003cp\u003eIn conclusion, measuring heparin-calibrated AXA in CTEPH patients treated with FXa inhibitors could provide useful information, especially to predict bleeding events.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAdditional Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYoshihisa Nakano reports receiving speaker and lecturer fees from Bayer, Janssen Pharmaceutical, Nippon Shinyaku, and Viatris outside the submitted work. In addition, english proofreading and article processing charges were subsidized by Adempas Post Marketing Surveillance by Bayer. Shiro Adachi reports receiving speaker and lecturer fee from Bayer, Bristol Myers Squibb, Daiichi-Sankyo, Janssen Pharmaceutical, Mochida Pharmaceutical, Nippon Shinyaku, Pfizer, and Viatris outside the submitted work. Toyoaki Murohara reports receiving speaker and lecturer fee from Bayer, Daiichi-Sankyo, and Janssen Pharmaceutical outside the submitted work. Takahisa Kondo reports receiving speaker and lecturer fee from Bayer, Bristol Myers Squibb, Daiichi-Sankyo, Janssen Pharmaceutical, Nippon Shinyaku, and Pfizer outside the submitted work. All of the other authors declare that they have no conflicts of interest to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe appreciate the support of the co-investigators who participated in this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTM and SA were guarantors of this study. YN and TK conceived the study. YN, SA, MH, TA, IN, KY, and MY pooled the data. YN and HY analyzed the data. YN wrote the manuscript. All authors discussed the results, reviewed the manuscript, and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\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\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by the Human Research Ethics Committees of Nagoya University Hospital (no. 2020-0615).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBauersachs, R. \u003cem\u003eet al.\u003c/em\u003e Oral Rivaroxaban for Symptomatic Venous Thromboembolism. \u003cem\u003eN. 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Pharmacol.\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, 728\u0026ndash;738 (2018).\u003c/li\u003e\n\u003cli\u003ePorres-Aguilar, M. \u003cem\u003eet al.\u003c/em\u003e Direct oral anticoagulants in chronic thromboembolic pulmonary hypertension. \u003cem\u003eJ. Thromb. Thrombolysis\u003c/em\u003e \u003cstrong\u003e52\u003c/strong\u003e, 791\u0026ndash;796 (2021).\u003c/li\u003e\n\u003cli\u003eHosokawa, K. \u003cem\u003eet al.\u003c/em\u003e Long-term outcome of chronic thromboembolic pulmonary hypertension using direct oral anticoagulants and warfarin: a Japanese prospective cohort study. \u003cem\u003eJ. Thromb. Haemost.\u003c/em\u003e S1538-7836(23)00270\u0026ndash;2 (2023) doi:10.1016/j.jtha.2023.03.036.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"factor Xa, direct-acting oral anticoagulant; pulmonary thromboembolism, pulmonary hypertension, Chronic thromboembolic pulmonary hypertension","lastPublishedDoi":"10.21203/rs.3.rs-4893570/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4893570/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDirect oral anticoagulants (DOACs) have been used clinically in patients with chronic thromboembolic pulmonary hypertension (CTEPH) for secondary prevention after acute venous thromboembolism, although the data is limited. We evaluated the effects of DOACs—especially factor Xa (FXa) inhibitors—by measuring anti-factor Xa activity (AXA). Fifty consecutive CTEPH patients treated with either rivaroxaban, apixaban, or edoxaban were enrolled. Heparin-calibrated AXA was measured at both peak and trough. The median peak heparin-calibrated AXA across all 50 patients was 1.90 IU/mL and was comparable among the three FXa inhibitors. At trough, heparin-calibrated AXA was significantly higher in apixaban treated patients (median 0.70 IU/mL) than in those with rivaroxaban (median 0.11 IU/mL) or edoxaban (median 0.11 IU/mL, \u003cem\u003ep\u003c/em\u003e \u0026lt;.001). Peak heparin-calibrated AXA was significantly lower with reduced-dose FXa inhibitor (edoxaban 30 mg/day) than with the reference dose (edoxaban 60 mg/day, apixaban 10 mg/day, or rivaroxaban 15 mg/day, \u003cem\u003ep\u003c/em\u003e =.01). The heparin-calibrated AXA of both rivaroxaban and apixaban was strongly significantly correlated with the plasma concentration of each drug. The cumulative rate of major and clinically relevant non-major bleeding was significantly higher in patients with peak heparin-calibrated AXA ≥2.09 IU/mL. Heparin-calibrated AXA could provide useful information when treating CTEPH patients with FXa inhibitors.\u003c/p\u003e","manuscriptTitle":"Monitoring anti-factor Xa activity in patients with chronic thromboembolic pulmonary hypertension treated with factor Xa inhibitors","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-10-15 05:01:59","doi":"10.21203/rs.3.rs-4893570/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-09-12T08:28:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-03T04:36:29+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-26T07:35:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"83290261112765806884650370899207861865","date":"2024-08-26T07:24:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"243130285459982769804658663815324003582","date":"2024-08-21T12:18:41+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-08-20T22:35:22+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-08-20T22:34:35+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-08-20T18:25:12+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-08-20T07:21:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-08-11T03:18:45+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"cf2d0a60-da38-47c5-8fe1-036347577882","owner":[],"postedDate":"October 15th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":37495085,"name":"Health sciences/Cardiology/Cardiovascular biology/Cardiovascular diseases"},{"id":37495086,"name":"Health sciences/Diseases/Cardiovascular diseases/Vascular diseases/Thromboembolism"}],"tags":[],"updatedAt":"2024-11-04T16:22:35+00:00","versionOfRecord":{"articleIdentity":"rs-4893570","link":"https://doi.org/10.1038/s41598-024-74481-7","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2024-10-28 16:05:00","publishedOnDateReadable":"October 28th, 2024"},"versionCreatedAt":"2024-10-15 05:01:59","video":"","vorDoi":"10.1038/s41598-024-74481-7","vorDoiUrl":"https://doi.org/10.1038/s41598-024-74481-7","workflowStages":[]},"version":"v1","identity":"rs-4893570","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4893570","identity":"rs-4893570","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}