Apixaban Versus Warfarin for Mechanical Heart Valve Thromboprophylaxis in a Swine Aortic Heterotopic Valve Model

DOACs in the Anticoagulation of Mechanical Valves: A Systematic Review and Future Perspectives

Valvular heart disease is a common disease often necessitating valve replacement. Mechanical heart valves (MHVs) are often used in younger patients because of their longer durability. Their main disadvantage is the need for lifelong anticoagulation. Warfarin is considered a standard treatment, but it is far from perfect. Direct oral anticoagulants (DOACs) are a new and more patient-friendly alternative to warfarin when anticoagulation is required, but have not yet been approved for the indication of mechanical valves.

EVIDENCE ACQUISITION

A literature search of Pubmed, Embase, Web of Science (Core Collection), and Cochrane Library (from inception to May 2023) was performed using a search string that was well defined and not modified during the study. An extensive overview of the search terms used in each database can be found in the Appendix. Only prospective clinical trials were included in this review. A total of 10 publications were included in this review.

RELEVANCE TO CLINICAL PRACTICE

This systematic review summarizes the different types of DOACs and their possible use in the anticoagulation of mechanical valves. We aim to propose future directions in anticoagulation research for mechanical valves.

CONCLUSIONS

DOAC use in MHVs has been halted due to the failure of both dabigatran and apixaban in two major clinical trials. However, rivaroxaban was successful in two small clinical trials. Ample research is still needed to explore new valve designs as well as new anticoagulation targets.

Apixaban or Warfarin in Patients with an On-X Mechanical Aortic Valve

Apixaban, Warfarin, and On-X Mechanical Aortic ValvesAlthough vitamin K antagonists are the only oral anticoagulants approved with mechanical heart valves, this trial examined whether apixaban could be safely used in patients with an On-X mechanical aortic valve. A total of 863 such patients were assigned apixaban 5 mg twice daily or warfarin (target international normalized ratio 2.0 to 3.0). A total of 20 thrombotic events occurred in the apixaban group (4.2%/patient-year) and 6 events in the warfarin group (1.3%/patient-year). Major bleeding rates were 3.6%/patient-year with apixaban and 4.5%/patient-year with warfarin.

Hepatic and Renal Histotripsy in an Anticoagulated Porcine Model

PURPOSE

To determine the risk of mechanical vessel wall damage resulting in hemorrhage during and after hepatic and renal histotripsy in an anticoagulated in vivo porcine model.

MATERIALS AND METHODS

Non-tumor-bearing pigs (n = 8; mean weight, 52.5 kg) were anticoagulated with warfarin (initial dose, 0.08 mg/kg) to a target prothrombin time (PT) of 30%-50% above baseline. A total of 15 histotripsy procedures were performed (kidney: n = 8, 2.0-cm sphere; liver: n = 7, 2.5-cm sphere). Treatments were immediately followed by computed tomography (CT) imaging. Animals were observed for 7 days while continuing anticoagulation, followed by repeat CT and necropsy.

RESULTS

All animals survived to complete the entire protocol with no signs of disability or distress. Three animals had hematuria (pink urine without clots). Baseline PT values (mean, 16.0 seconds) were elevated to 22.0 seconds (37.5% above baseline, P = .003) on the day of treatment and to 28.8 seconds (77.8% above baseline, P < .001) on the day of necropsy. At the time of treatment, 5 of 8 (63%) animals were at a therapeutic anticoagulation level, and all 8 animals (100%) reached therapeutic levels by the time of necropsy. There were no cases of intraparenchymal, peritoneal, or retroperitoneal hemorrhage associated with any treatments despite 5 of 7 (71%) liver and all 8 (100%) kidney treatments extending to the organ surface.

CONCLUSIONS

Liver and kidney histotripsy seems safe with no elevated bleeding risk in this anticoagulated animal model, supporting the possibility of histotripsy treatments in patients on anticoagulation.

Effective, safe and efficient porcine model of Forrest Ib bleeding gastric and colonic ulcers

BACKGROUND

Developing effective gastrointestinal (GI) bleeding animal models is necessary to advance endoscopic hemostasis methods and train endoscopists on their use. Our aim, therefore, was to develop an effective and safe porcine GI bleeding model in the stomach and colon of large and small-sized oozing-type ulcers.

METHODS

Gastric and colonic bleeding ulcers were created using either a hybrid endoscopic submucosal dissection (ESD) technique or a cap-assisted endoscopic mucosal resection (EMR-C) technique in 14 pigs. Prior to ulcer creation, animals were treated with either oral apixaban or intravenous (IV) unfractionated heparin anticoagulation in combination with clopidogrel and aspirin. The primary outcome was the technical success of inducing oozing-type Forrest Ib bleeding ulcers. Secondary outcomes included ulcer diameter, number, creation time and the number of complications associated with each technique.

RESULTS

Using hybrid ESD and IV heparin anticoagulation, bleeding was observed in 21/23 (91.3%) gastric ulcers and 6/7 (85.7%) colonic ulcers created. The mean diameter and ulcer creation time were 2.3 ± 0.3 cm and 5.3 ± 0.5 min, respectively, for gastric ulcers and 2.2 ± 0.4 cm and 4.06 ± 0.6 min, respectively, for colonic ulcers. Using EMR-C and IV heparin anticoagulation, bleeding was observed in 14/15 (93.3%) gastric ulcers and 6/6 (100%) colonic ulcers created. The mean diameter and ulcer creation time were 0.8 ± 0.2 cm and 2.1 ± 0.5 min, respectively, for gastric ulcers and 0.7 ± 0.2 cm and 1.7 ± 0.3 min, respectively, for colonic ulcers. None of the ulcers created in animals anticoagulated with apixaban developed bleeding. None of the 14 pigs developed any complications.

CONCLUSION

We have demonstrated the effectiveness and safety of a porcine GI bleeding model utilizing IV heparin anticoagulation and either hybrid ESD or EMR-C techniques to create oozing-type bleeding ulcers in the stomach and colon with customizable size.

DOACs in Mechanical and Bioprosthetic Heart Valves: A Narrative Review of Emerging Data and Future Directions

In the recent years, there has been significant transformation in the management of valvular heart disease (VHD), as a result of new minimally invasive technologies, such as the transcatheter aortic valve implantation (TAVI). Conventionally, mechanical heart valves require anticoagulation with warfarin to prevent thrombogenic events. Lately, there has been an uptrend in the usage of direct-acting oral anticoagulants (DOACs) in both mechanical and bioprosthetic heart valves. In clinical practice, there has shown to be notable heterogeneity in the antithrombotic regimen for patients. Recommendations from clinical guidelines and emerging data on DOAC use in these settings will be critically reviewed here. Future large, randomized-controlled trials are warranted to delineate the role of DOACs in patients receiving a bioprosthetic valve/TAVI or mechanical heart valve, with and without a baseline indication for anticoagulation or antiplatelets. Until clinical trial data from well-designed studies are available, providers must remain vigilant about DOAC use in patients with VHD, especially in patients with a bioprosthetic or mechanical heart valve.

Analysis of Anticoagulation Therapy and Anticoagulation-Related Outcomes Among Asian Patients After Mechanical Valve Replacement

IMPORTANCE

Current international normalized ratio (INR) guidelines are based on trials involving European and US populations. To our knowledge, no adequate study involving Asian patients has been conducted to date.

OBJECTIVE

To evaluate the association between INR and anticoagulation-related outcomes in an Asian population after mechanical aortic valve replacement (AVR) or mitral VR (MVR).

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study was conducted between 2001 and 2018, with follow-up until December 31, 2018, among patients who underwent AVR, MVR, or combined AVR-MVR at 3 medical centers and 4 regional hospitals and contributed electronic medical records to the Chang Gung Research Database. Exclusion criteria were missing demographic characteristics, younger than 20 years, fewer than 2 INR records, and having died during the hospitalization of the index surgery.

MAIN OUTCOMES AND MEASURES

Bleeding and thromboembolic complications were analyzed. The possibility of nonlinearity and cutoff potential for the INR were explored using a logistic regression model, which considered the INR a restricted cubic spline (RCS) variable.

RESULTS

The study population consisted of 900 patients, with 525 (58.3%) men and 375 (41.7%) women and a mean (SD) age of 52.0 (12.5) years. Overall, 474 (52.7%) received AVR alone, 329 (36.6%) received MVR alone, and 97 (10.8%) received combined AVR-MVR. All patients had at least 2 INR examinations after discharge, providing 16 676 INR records for the AVR group and 18 207 for the MVR and combined AVR-MVR groups. In the AVR group, the RCS model showed that higher risks of composite thromboembolic events were associated with an INR of less than 2.0 or greater than 2.6 vs an INR of 2.0, and a higher risk of bleeding events was associated with an INR of less than 1.8 or greater than 2.4 vs an INR of 2.0. When treating the INR as a categorical variable, the risk of composite thromboembolic and composite bleeding events was significantly higher among patients with INRs less than 1.5 (adjusted odds ratio [aOR], 2.55; 95% CI, 1.37-4.73) and with INRs of 3.0 or greater (aOR, 3.48; 95% CI, 1.95-6.23) vs those with INRs between 2.0 and 2.5.In the MVR and combined AVR-MVR groups, higher risks of composite thromboembolic events were associated with an INR of less than 2.1 or greater than 2.7 vs an INR of 2.5, and a higher risk of bleeding events was associated with an INR of less than 2.1 or greater than 2.8 vs an INR of 2.5. When treating the INR as a categorical variable, the risk of a composite bleeding events was significantly higher among patients with INRs of 3.5 or greater (aOR, 2.25; 95% CI, 1.35-3.76) vs those with INRs between 2.5 and 3.0.

CONCLUSIONS AND RELEVANCE

Among Asian patients in this study, the incidence of thromboembolic events in the MVR group with INRs in the range of 2.0 to 2.5 was not significantly higher than that among those with INRs in the range of 2.5 to 3.0; in the AVR group, the incidence for those with INRs in 1.5 to 2.0 range was not significantly higher than for those with INRs in the range of 2.0 to 2.5.

Factor Xa Inhibitors for Patients after Mechanical Heart Valve Replacement?

Patients with a mechanical heart valve need a lifelong anticoagulation due to the increased risk of valve thrombosis and thrombo-embolism. Currently, vitamin K antagonists (VKA) are the only approved class of oral anticoagulants, but relevant interactions and side effects lead to a large number of patients not achieving the optimal therapeutic target international normalized ration (INR). Therefore, steady measurements of the INR are imperative to ensure potent anticoagulation within a distinctive range. Direct oral anticoagulants (DOACs) with newer agents could serve as a possible alternative to VKAs in this patient cohort. DOACs are approved for several indications, e.g., atrial fibrillation (AF). They only have a minor interaction potential, which is why monitoring is not needed. Thereby, DOACs improve the livability of patients in need of chronical anticoagulation compared with VKAs. In contrast to dual platelet inhibition using aspirin in combination with an ADP receptor antagonist and the direct thrombin inhibitor dabigatran, the oral factor Xa inhibitors apixaban and rivaroxaban show promising results according to current evidence. In small-scale studies, factor Xa inhibitors were able to prevent thrombosis and thrombo-embolic events in patients with mechanical heart valves. Finally, DOACs seem to represent a feasible treatment option in patients with mechanical heart valves, but further studies are needed to evaluate clinical safety. In addition to the ongoing PROACT Xa trial with apixaban in patients after aortic On-X valve implantation, studies in an all-comer collective with rivaroxaban could be promising.

Apixaban use in an atrial fibrillation patient with double mechanical heart valves: a case report

Background

Warfarin is the only approved oral anticoagulant for long-term prophylaxis against valve thrombosis and thromboembolism in patients with mechanical heart valves. To date, apixaban for patients with double (aortic and mitral) mechanical heart valves has not been reported in the literature.

Case summary

We report the case of a 50-year-old female who underwent double (aortic and mitral) mechanical valve replacement in February 2017. Warfarin was prescribed after mechanical valve replacement. However, she complained of side effects of warfarin, including tingling sensation and numbness of legs, urticaria, skin rash, and nausea and voluntarily stopped taking medication. In December 2018, she was admitted to the emergency room due to ongoing chest pain. Coronary angiogram revealed embolic myocardial infarction at the left circumflex coronary artery. Nevertheless, she continued to refuse to take warfarin after anticoagulant therapy for coronary artery embolism. Given the patient’s objection, we prescribed apixaban 5 mg b.i.d. since February 2019. When she was diagnosed with atrial fibrillation in April 2020, no intracardiac thrombosis was confirmed on computed tomography and electrical cardioversion was performed safely. While on apixaban, no evidence of prosthetic valve thrombosis or thrombo-embolic events was observed during a 24-month period.

Conclusion

We report the efficacy and safety of apixaban in a patient with atrial fibrillation and double mechanical heart valves for preventing prosthetic valve thrombus and systemic embolism.

Ex Vivo Assessment of Different Oral Anticoagulant Regimens on Pump Thrombosis in a HeartWare Ventricular Assist Device

BACKGROUND

In light of decreased intracranial hemorrhage with direct oral anticoagulants and concerns about their safety in continuous flow left ventricular assist devices, we conducted an ex vivo study of thrombus formation using multiple anticoagulation agents.

METHODS

A continuous flow left ventricular assist device (HeartWare ventricular assist device) hemocompatibility loop was run using human blood under 7 conditions: control (no anticoagulation or antiplatelet); in vitro addition of aspirin; in vitro addition of apixaban at low dose (equivalent 2.5 mg twice daily); addition of apixaban at high dose (equivalent 5 mg twice daily); patients on warfarin; patients on apixaban (5 mg twice daily); and patients on dabigatran (150 mg twice daily). The primary outcome was time to formation of intrapump thrombosis. Secondary outcomes were reduction in clotting times over 1 hour, hemolysis, reduced platelet aggregation, and von Willebrand activity.

RESULTS

Twenty-one runs were completed. Times to thrombosis in median (interquartile range) were control, 131 (127-134.5); in vitro aspirin, 124 (114.5-137); and patients on dabigatran, 131 (130.5-135.5) minutes, respectively. Times in patients on warfarin were, 137 (136.5-143.5); in vitro low-dose apixaban, 141 (138.5-142); and patients on apixaban, 140 (138-142.5) minutes, respectively. No thrombus formed in the in vitro high-dose apixaban group. There were no significant differences between the individual groups. When all apixaban groups were compared with nonapixaban groups, the time to thrombosis formation was significantly longer, 143 (137-150) versus 133.5 (128.5-140) minutes, P=0.02. There were similar changes in lactate dehydrogenase levels and other secondary end points.

CONCLUSIONS

In an in vitro study of anticoagulation using human blood in a mock loop with a HeartWare HVAD, we demonstrated similar thrombosis times for apixaban and warfarin. Time to clotting was longer in the combined apixaban groups compared with combined other groups, but thrombosis times between individual groups were not significantly different.

Alternatives for Vitamin K Antagonists as Thromboprophylaxis for Mechanical Heart Valves and Mechanical Circulatory Support Devices: A Systematic Review

The holy grail of anticoagulation in patients with intracardiac devices, such as mechanical heart valves (MHVs) and left ventricular assist devices (LVADs), comprises safe prevention of thrombosis without interrupting normal hemostasis. Device-induced thrombosis and anticoagulant-related bleeding problems are dreaded complications that may cause a significantly reduced quality of life and increased morbidity and mortality. Vitamin K antagonists are the current standard for oral anticoagulation therapy in patients with MHVs and LVADs. Even within the therapeutic range, hemorrhage is the primary complication of these drugs, which emphasizes the need for safer anticoagulants for the prevention of device-induced thrombosis. Device-induced thrombosis is a complex multifactorial phenomenon that likely requires anticoagulant therapy targeting multiple pathways. Here, we review the preclinical and clinical data describing the efficacy of a variety of anticoagulants as thromboprophylaxis after implantation of intracardiac devices.

Rivaroxaban Versus Warfarin in Patients with Mechanical Heart Valves: Open-Label, Proof-of-Concept trial-The RIWA study

BACKGROUND AND PURPOSE

To date, vitamin K antagonists are the only available oral anticoagulants in patients with mechanical heart valves. In this way, we developed a pilot trial with rivaroxaban.

METHODS

 The RIWA study was a proof-of-concept, open-label, randomized clinical trial and was designed to assess the incidence of thromboembolic and bleeding events of the rivaroxaban-based strategy (15 mg twice daily) in comparison to dose-adjusted warfarin. Patients were randomly assigned in a 1:1 ratio and were followed prospectively for 90 days.

RESULTS

 A total of 72 patients were enrolled in the present study. Of these, 44 patients were randomized: 23 patients were allocated to the rivaroxaban group and 21 to the warfarin group. After 90 days of follow-up, the primary outcome occurred in one patient (4.3%) in the rivaroxaban group and three patients (14.3%) in the warfarin group (risk ratio [RR] 0.27; 95% confidence interval [CI] 0.02-2.85; P = 0.25). Minor bleeding (without discontinuation of medical therapy) occurred in six patients (26.1%) in the rivaroxaban group versus six patients (28.6%) in the warfarin group (RR 0.88; 95% CI 0.23-3.32; P = 0.85). One patient in the warfarin group died from myocardial infarction. No cases of hemorrhagic stroke, valve thrombosis, peripheral embolic events, or new intracardiac thrombus were related in both groups.

CONCLUSIONS

In this pilot study, rivaroxaban 15 mg twice daily had thromboembolic and bleeding events similar to warfarin in patients with mechanical heart valves. These data confirm the authors' proof-of-concept and suggest that a larger trial with a similar design is not unreasonable. CLINICALTRIAL.

GOV IDENTIFIER

NCT03566303.

A review of indications and comorbidities in which warfarin may be the preferred oral anticoagulant

WHAT IS KNOWN AND OBJECTIVE

Direct oral anticoagulants (DOACs) are increasingly prescribed instead of warfarin for chronic anticoagulation for ease of dosing, fewer interactions, and less stringent monitoring. However, it is important to consider indications and comorbidities for which warfarin is still the preferred anticoagulant. This review aims to capture these clinical scenarios in which warfarin may still be preferred over DOACs.

METHODS

We undertook a comprehensive literature search using the PubMed database. Key search terms were based on DOAC clinical trial exclusion criteria, as well as indications and conditions in which the use of DOACs for anticoagulation has suggested harm. Society guidelines and tertiary literature were used to inform expert opinion where necessary. Studies were included if they investigated the use of DOACs or warfarin in the identified indications or conditions.

RESULTS AND DISCUSSION

Currently, evidence for the use of warfarin over DOACs for anticoagulation is strongest for patients with prosthetic valves, antiphospholipid syndrome, or a high risk of gastrointestinal bleeding. For several clinical situations, including mitral stenosis, obesity, altered gastrointestinal anatomy, pulmonary arterial hypertension, renal or hepatic impairment, and left ventricular thrombus, evidence is lacking but may eventually support the use of DOACs. Depending on indication and condition, appropriateness of DOAC use may vary by agent.

WHAT IS NEW AND CONCLUSION

New evidence continues to support new indications and conditions in which DOACs may be appropriate to use for anticoagulation. There are key clinical scenarios, however, in which emerging literature continues to support warfarin as the preferred anticoagulant.

Rationale and design of PROACT Xa: A randomized, multicenter, open-label, clinical trial to evaluate the efficacy and safety of apixaban versus warfarin in patients with a mechanical On-X Aortic Heart Valve

Vitamin K antagonists are the only approved oral anticoagulants for long-term prophylaxis against valve thrombosis and thromboembolism in patients with a mechanical heart valve. Despite the proven efficacy and safety of anticoagulation with the oral direct factor Xa inhibitor apixaban compared with warfarin in high-risk populations including subjects with atrial fibrillation or with venous thromboembolism, it remains unknown whether patients with a mechanical heart valve can be safely managed with apixaban. The On-X Aortic Heart Valve and On-X Ascending Aortic Prosthesis with the Vascutek Gelweave Valsalva Graft may have lower rates of valve thrombosis and thromboembolism than conventional bileaflet and tilting disc valves due its unique pyrolytic carbon composition and flared inlet design. DESIGN: PROACT Xa is a randomized, multicenter, open-label, active-controlled trial comparing apixaban with warfarin in patients with an On-X Aortic Heart Valve or On-X Ascending Aortic Prosthesis with the Vascutek Gelweave Valsalva Graft. The study will randomize approximately 1,000 patients from approximately 60 sites in North America who underwent aortic valve replacement at least 3 months prior. Patients will be randomized 1:1 to receiving apixaban 5 mg twice daily or warfarin with a target international normalized ratio of 2.0-3.0. The last randomized participant will be followed for at least 2 years. The primary efficacy outcome is the composite of valve thrombosis and valve-related thromboembolism, and the primary safety outcome is major bleeding. Assuming the primary outcome occurs in warfarin-anticoagulated patients at a rate of 1.75%/patient-year, the study has more than 90% power to assess noninferiority of apixaban treatment with an absolute noninferiority margin of 1.75%/patient-year. A second co-primary analysis is to compare the hazard rate for the apixaban arm to twice the objective performance criterion for thromboembolism and valve thrombosis, that is, 3.4%/patient-year. SUMMARY: PROACT Xa will determine whether patients with an On-X Aortic Heart Valve can be anticoagulated with apixaban as an alternative to warfarin.

Rivaroxaban and Dabigatran for Suppression of Mechanical Heart Valve-Induced Thrombin Generation

BACKGROUND

Patients with mechanical heart valves (MHVs) require warfarin to prevent thromboembolism. Dabigatran was less effective than warfarin in patients with MHVs, which prompted a black box warning against the use of direct oral anticoagulants for this indication. However, rivaroxaban and apixaban, which inhibit factor Xa, have not been evaluated in patients with MHVs. To determine whether rivaroxaban and apixaban would be effective, we used MHV-induced thrombin generation assays to compare them with warfarin either alone or in combination with dabigatran.

METHODS

Thrombin generation in the absence or presence of MHV leaflets or sewing ring segments (SRSs) was quantified. Studies were done in control plasma; plasma from patients on warfarin; plasma containing varying concentrations of rivaroxaban, apixaban, or dabigatran alone; or plasma containing rivaroxaban plus dabigatran.

RESULTS

Mean endogenous thrombin potential (ETP) increased 1.2-fold, 1.5-fold, and 1.8-fold in the presence of leaflets, Teflon (Terumo Aortic (Sunrise, FL)) SRSs, or Dacron (Terumo Aortic (Sunrise, FL)) SRSs, respectively. Rivaroxaban and apixaban reduced ETP at concentrations above 50 ng/mL but were less effective than warfarin. When rivaroxaban and dabigatran were combined, they suppressed ETP in a more than additive manner.

CONCLUSIONS

Whereas warfarin suppresses MHV-induced thrombin generation, MHVs induce the generation of factor Xa in concentrations that overwhelm clinically relevant concentrations of rivaroxaban or apixaban. When used in combination, rivaroxaban and dabigatran are more effective than either agent is alone, suggesting that concomitant inhibition of factor Xa and thrombin is better than inhibition of either clotting enzyme alone.