Effectiveness of dabigatran etexilate for thromboprophylaxis of mechanical heart valves

A Fibrin-Thrombin Based In Vitro Perfusion System to Study Flow-Related Prosthetic Heart Valves Thrombosis

Prosthetic heart valve (PHV) replacement has increased the survival rate and quality of life for heart valve-diseased patients. However, PHV thrombosis remains a critical problem associated with these procedures. To better understand the PHV flow-related thrombosis problem, appropriate experimental models need to be developed. In this study, we present an in vitro fibrin clot model that mimics clot accumulation in PHVs under relevant hydrodynamic conditions while allowing real-time imaging. We created 3D-printed mechanical aortic valve models that were inserted into a transparent glass aorta model and connected to a system that simulates human aortic flow pulse and pressures. Thrombin was gradually injected into a circulating fibrinogen solution to induce fibrin clot formation, and clot accumulation was quantified via image analysis. The results of valves positioned in a normal versus a tilted configuration showed that clot accumulation correlated with the local flow features and was mainly present in areas of low shear and high residence time, where recirculating flows are dominant, as supported by computational fluid dynamic simulations. Overall, our work suggests that the developed method may provide data on flow-related clot accumulation in PHVs and may contribute to exploring new approaches and valve designs to reduce valve thrombosis.

Difference in coagulation systems of large animal species used in cardiovascular research: a systematic review

Preclinical testing using animal models is indispensable in cardiovascular research. However, the translation to clinical practice of these animal models is questionable since it is not always clear how representative they are. This systematic review intends to summarize the interspecies differences in the coagulation profile of animal models used in cardiovascular research. It aims to guide future research in choosing the optimal animal species. A literature search of PubMed, Embase, Web of Science (Core Collection) and Cochrane Library was performed using a search string that was well defined and not modified during the study. An overview of the search terms used in each database can be found in the appendix. Articles describing coagulation systems in large animals were included. We identified 30 eligible studies of which 15 were included. Compared to humans, sheep demonstrated a less active external pathway of coagulation. Sheep had a higher platelet count but the platelet activatability and response to biomaterials were lower. Both sheep and pigs displayed no big differences in the internal coagulation system compared to humans. Pigs showed results very similar to those of humans, with the exception of a higher platelet count and stronger platelet aggregation in pigs. Coagulation profiles of different species used for preclinical testing show strong variation. Adequate knowledge of these differences is key in the selection of the appropriate species for preclinical cardiovascular research. Future thrombogenicity research should compare sheep to pig in an identical experimental setup.

Histologic changes of porcine portal vein anastomosis after electrochemotherapy with bleomycin

Electrochemotherapy (ECT1) is used for treatment of unresectable abdominal malignancies. This study aims to show that ECT of porcine portal vein anastomosis is safe and feasible in order to extend the indications for margin attenuation after resection of locally advanced pancreatic carcinoma. No marked differences were found between the control group and ECT treated groups. Electroporation thus caused irreversible damage to the vascular smooth muscle cells in tunica media that could bedue to the narrow irreversible electroporation zone that may occur near the electrodes, or due to vasa vasorum thrombosis in the tunica externa. Based on the absence of vascular complications, and similar histological changes in lienal veinanastomosis, we can conclude that ECT of portal vein anastomosis is safe and feasible.

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.

Peri-Interventional Triple Therapy with Dabigatran Modifies Vasomotion after Bare-Metal Stent Implantation in a Pig Coronary Artery Model

(1) Background: Coronary artery stenting leads to local inflammation, disturbs vasomotion, and slows endothelialization, increasing vascular thrombus risk. We used a pig stenting coronary artery model to assess how peri-interventional triple therapy with dabigatran ameliorates these effects. (2) Methods: In a total of 28 pigs bare-metal stents were implanted. Four days before the percutaneous coronary intervention (PCI), we started 16 of the animals on dabigatran, maintained through 4 days after the procedure. As controls, the remaining 12 pigs received no therapy. In both groups, dual antiplatelet therapy (DAPT) (clopidogrel, 75 mg plus aspirin, 100 mg) was administered until animals were euthanized. Just after the PCI and on day 3 after the procedure, we performed optical coherence tomography (OCT) in eight animals in the dabigatran group and four controls and euthanized them. We followed the eight remaining animals in each group with OCT and angiography for one month before euthanizing them and performed in vitro myometry and histology on harvested coronary arteries from all animals. (3) Results: The dabigatran group showed a significantly increased vasoconstriction at 3 days after PCI (10.97 ± 3.85 mN vs. 7.32 ± 5.41 mN, p = 0.03), but we found no differences between endothelium-dependent and -independent vasodilatation. We also found no group differences in OCT, quantitative angiography, or histomorphometry findings. (4) Conclusions: Starting a short course of dabigatran just before PCI and continuing for a 3-day window along with usual post-PCI DAPT is associated with enhanced vasoconstriction after bare-metal stent implantation without reducing neointimal formation at one month.

Non-vitamin K antagonist oral anticoagulants in patients with valvular heart disease

The non-vitamin K antagonist oral anticoagulants (NOACs) dabigatran, rivaroxaban, apixaban, and edoxaban have transformed the management of atrial fibrillation (AF), but are only approved by regulatory authorities for stroke prophylaxis in patients with so-called “non-valvular AF.” This terminology has spawned confusion about which patients with valvular heart disease benefit from NOACs and which should be treated with vitamin K antagonists (VKAs) instead. Patients with valvular heart disease other than mechanical prosthetic valves or severe mitral stenosis (including those with bioprosthetic valves) were included in pivotal trials demonstrating the benefit of NOACs over VKAs, and consensus guidelines recommend NOACs over VKAs in these patients. Subsequent devoted randomized controlled trials in patients with AF and bioprosthetic valves, including transcatheter valves, have confirmed the safety of NOACs in this population. In patients with rheumatic mitral stenosis, observational studies indicate that NOACs may be safe and effective, but randomized controlled trials are ongoing. By contrast, a randomized controlled trial showed that dabigatran is harmful in patients with mechanical prosthetic mitral valves; however, these data may not extrapolate to patients with mechanical valve prostheses in other locations or to other NOACs, and randomized controlled trials are ongoing. In this review, we discuss these data in greater depth, and make recommendations for the use of NOACs in patients with valvular heart disease.

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.

Peri-interventional Triple Therapy With Dabigatran Improves Vasomotion and Promotes Endothelialization in Porcine Coronary Stenting Model

Objective: We evaluated the short and long-term effect of peri-interventional dabigatran therapy on vasomotion, endothelialization, and neointimal formation in a porcine coronary artery stenting model.

Background: Stenting of coronary arteries induces local inflammation, impairs vasomotion and delays endothelialization.

Methods: Twenty-eight animals underwent percutaneous coronary intervention (PCI) with drug eluting stents. Sixteen pigs started dabigatran therapy 4 days prior to PCI and continued for 4 days post-stenting, while 12 animals served as controls. Post-stenting dual antiplatelet therapy (75 mg clopidogrel and 100 mg aspirin) was continued in both groups until termination. Immediately post-stenting and at day 3 optical coherence tomography (OCT) was performed in all animals, followed by euthanasia of 8 dabigatran and 4 control animals. The remaining pigs (8 of each group) were followed up for 1 month, with control angiography and OCT. Tissue burden (degree of peri-strut structure—thrombus and/or fibrin) was evaluated. After euthanasia coronary arteries were harvested for in-vitro myometry and histology.

Results: Thrombin generation was lower (p < 0.001) and tissue burden (0.83 ± 0.98 vs. 3.0 ± 2.45; p = 0.031) was significantly decreased in dabigatran treated animals. After 3 days post-PCI endothelium-dependent vasodilation was significantly improved (77 ± 40% vs. 41 ± 31%, p = 0.02) in dabigatran animals. Neither quantitative angiography nor histomorphometry showed differences between the groups. Endothelialization was faster in the dabigatran group as compared with controls (p = 0.045).

Conclusion: Short-term peri-interventional triple therapy with dabigatran, aspirin, and clopidogrel led to an enhanced endothelium dependent vasodilation and faster endothelialization. However, neointimal formation 1-month after stent implantation was comparable between groups.

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.

Predictors of Use and Outcomes of Mechanical Valve Replacement in the United States (2008-2017)

Background

Contemporary nationwide data on the use, predictors, and outcomes of mechanical valve replacement in patients less than 70 years of age are limited.

Methods and Results

We identified hospitalizations for aortic valve replacement (AVR) or mitral valve replacement (MVR) in the Nationwide Inpatient Sample between January 1, 2008, and December 31, 2017. The study's end points included predictors of mechanical valve replacement and risk‐adjusted in‐hospital mortality. Among 253 100 hospitalizations for AVR, the use rate of mechanical prosthesis decreased from 45.3% in 2008 to 17.0% in 2017. Among 284 962 hospitalizations for MVR, mechanical prosthesis use decreased from 59.5% in 2008 to 29.2% in 2017 (P for trend<0.001). In multilogistic regression analyses, female sex, prior sternotomy, prior defibrillator, and South/West geographic location were predictive of mechanical valve use. The presence of bicuspid valve was a negative predictor of mechanical AVR (odds ratio [OR], 0.68; 95% CI, 0.66–0.69; P<0.001), whereas mitral stenosis was associated with higher mechanical MVR (OR, 1.28; 95% CI, 1.22–1.33; P<0.001). Unadjusted in‐hospital mortality decreased over time with AVR but not with MVR, regardless of prosthesis choice. Using years 2008 and 2009 as a reference, risk‐adjusted mortality also decreased over time with AVR but did not decrease after MVR.

Conclusions

There is a substantial decline in the use of mechanical valve replacement among patients aged ≤70 years in the United States. Long‐term durability data on bioprosthetic valve replacement are needed to better define the future role of mechanical valves in this age group.

Anticoagulation and antiplatelet therapy in patients with prosthetic heart valves

BACKGROUND

The choice of antithrombotic therapy, anticoagulants or antiplatelets, after prosthetic heart valve replacement or repair, remains a disputed topic in the literature. Antithrombotic therapies are used after heart valve intervention to reduce the rates of thromboembolic events, therefore improving patient outcomes. Different interventions may require different therapeutic regimens to achieve the most efficacious clinical outcome for patients.

METHODS AND DISCUSSION

This review aims to summarize and critique the available literature concerning therapeutic agents used for bioprosthetic and mechanical valves as well as for valve repair, so as to assist clinicians and researchers in making decisions with regard to their patients and research endeavors.

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.

Hemocompatibility of Super-Repellent surfaces: Current and Future

Virtually all blood-contacting medical implants and devices initiate immunological events in the form of thrombosis and inflammation. Typically, patients receiving such implants are also given large doses of anticoagulants, which pose a high risk and a high cost to the patient. Thus, the design and development of surfaces with improved hemocompatibility and reduced dependence on anticoagulation treatments is paramount for the success of blood-contacting medical implants and devices. In the past decade, the hemocompatibility of super-repellent surfaces (i.e., surfaces that are extremely repellent to liquids) has been extensively investigated because such surfaces greatly reduce the blood-material contact area, which in turn reduces the area available for protein adsorption and blood cell or platelet adhesion, thereby offering the potential for improved hemocompatibility. In this review, we critically examine the progress made in characterizing the hemocompatibility of super-repellent surfaces, identify the unresolved challenges and highlight the opportunities for future research on developing medical implants and devices with super-repellent surfaces.

Mechanical Valve Thrombosis on Rivaroxaban: Are Novel Anticoagulants Really an Option?

This is a case of a 54-year-old female with a history of mechanical aortic valve replacement who presented in cardiogenic shock. Her primary care provider started her on rivaroxaban for anticoagulation therapy. An urgent transesophageal echocardiogram revealed a significant gradient and thrombosis on one leaflet of the valve that was immobile. Given that she was not a surgical candidate, she underwent thrombolysis. However, she later died due to complications from the thrombotic valve. The utility of target-specific oral anticoagulants has yet to be established in clinical practice.

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

Objective—

Warfarin is the current standard for oral anticoagulation therapy in patients with mechanical heart valves, yet optimal therapy to maximize anticoagulation and minimize bleeding complications requires routine coagulation monitoring, possible dietary restrictions, and drug interaction monitoring. As alternatives to warfarin, oral direct acting factor Xa inhibitors are currently approved for the prophylaxis and treatment of venous thromboembolism and reduction of stroke and systemic embolization. However, no in vivo preclinical or clinical studies have been performed directly comparing oral factor Xa inhibitors such as apixaban to warfarin, the current standard of therapy.

Approach and Results—

A well-documented heterotopic aortic valve porcine model was used to test the hypothesis that apixaban has comparable efficacy to warfarin for thromboprophylaxis of mechanical heart valves. Sixteen swine were implanted with a bileaflet mechanical aortic valve that bypassed the ligated descending thoracic aorta. Animals were randomized to 4 groups: control (no anticoagulation; n=4), apixaban oral 1 mg/kg twice a day (n=5), warfarin oral 0.04 to 0.08 mg/kg daily (international normalized ratio 2–3; n=3), and apixaban infusion (n=4). Postmortem valve thrombus was measured 30 days post-surgery for control-oral groups and 14 days post-surgery for the apixaban infusion group. Control thrombus weight (mean) was significantly different (1422.9 mg) compared with apixaban oral (357.5 mg), warfarin (247.1 mg), and apixiban 14-day infusion (61.1 mg; P <0.05).

Conclusions—

Apixaban is a promising candidate and may be a useful alternative to warfarin for thromboprophylaxis of mechanical heart valves. Unlike warfarin, no adverse bleeding events were observed in any apixaban groups.

Defining nonvalvular atrial fibrillation: A quest for clarification

Non-vitamin K oral anticoagulants (NOACs) are currently recommended for patients with nonvalvular atrial fibrillation since the publication of the 4 major pivotal trials evaluating the efficacy and safety of factor IIa and factor Xa inhibitors. The definition of nonvalvular atrial fibrillation is unclear, varying from one trial to another and even between North American and European guidelines, which is a source of uncertainties in clinical practice. However, many patients with atrial fibrillation present signs of valvular involvement, and clarification of this term is needed to not deny NOACs to patients based on the wrong perception that they may have valvular atrial fibrillation. The currently unique contraindications to NOACs are patients with mechanical heart valves and those with moderate-to-severe mitral stenosis, as stated by the recent 2015 position paper of the European Heart Rhythm Association. Patients with native heart valve involvement, regardless of their severity, are suitable for NOAC therapy. Patients with bioprosthetic heart valves and mitral valve repair may be suitable for NOACs except for the first 3 and the first 3-6 months postoperatively, respectively. Patients with transaortic valve implantation or percutaneous transluminal aortic valvuloplasty are also considered as being eligible for NOACs, although the bleeding risk has to be carefully considered in this population often requiring a combination with antiplatelet therapy. Future studies are warranted to increase the level of evidence of use of NOACs, particularly in patients with transaortic valve implantation and valvular surgery, and to determine whether they could be used in the future in the only 2 remaining contraindications.

Monitoring of hematological and hemostatic parameters in neurocritical care patients

Anemia and bleeding are paramount concerns in neurocritical care and often relate to the severity of intracranial hemorrhage. Anemia is generally associated with worse outcomes, and efforts to minimize anemia through reduced volume of blood sampled are encouraged. Point-of-care-testing reliably detects the use of non-steroidal anti-inflammatory drugs that may worsen bleeding and reduce platelet activity, particularly in patients with intracerebral hemorrhage. How best to monitor the effect of platelet transfusion or platelet-activating therapy is not well studied. For patients known to take novel oral anticoagulants, drug-specific coagulation tests before neurosurgical intervention are prudent.

Dabigatran is Less Effective Than Warfarin at Attenuating Mechanical Heart Valve-Induced Thrombin Generation

Background

Patients with mechanical heart valves (MHV) require warfarin to prevent thromboembolism. Although dabigatran was as effective as warfarin for stroke prevention in atrial fibrillation when compared with warfarin in patients with MHV, the study was stopped early because of more strokes and bleeding with dabigatran. To determine why dabigatran was less effective than warfarin, we compared their effects on thrombin generation induced by MHV.

Methods and Results

Thrombin generation in the absence or presence of valve leaflets or sewing ring segments (SRS) was quantified. Studies were done in control plasma, plasma depleted of factors (F) XII, XI, or VII, plasma containing varying concentrations of dabigatran, or plasma from patients on dabigatran or warfarin with varying dabigatran concentrations or international normalized ratio (INR) values. Mean endogenous thrombin potential (ETP) increased 1.2-, 1.5-, and 1.8-fold in the presence of leaflets, Teflon SRS, and Dacron SRS, respectively. Whereas ETP in FVII-depleted and control plasma was similar, ETP was reduced to background levels in FXII-depleted plasma and abrogated in FXI-depleted plasma. Dabigatran had little effect on ETP at concentrations below 400 ng/mL, whereas in plasma from warfarin-treated patients, ETP was suppressed with INR values over 1.5.

Conclusions

MHV induce thrombin generation via the intrinsic pathway and generate sufficient thrombin to overwhelm clinically relevant dabigatran concentrations. In contrast, warfarin is more effective than dabigatran at suppressing MHV-induced thrombin generation. These data explain why dabigatran failed in MHV patients and suggest that strategies targeting FXII or FXI may suppress the root cause of thrombosis in such patients.

Role of novel anticoagulants for patients with mechanical heart valves

The introduction of the target-specific oral anticoagulants (TSOACs) has led to a major shift in the management of patients at risk for thrombosis. The landscape continues to evolve as the evidence regarding their efficacy and safety in various clinical situations emerges. Antithrombotic therapy for thromboprophylaxis in patients with mechanical heart valves is challenging. To date, the RE-ALIGN trial comparing dabigatran etexilate to warfarin is the only randomized controlled study in this patient population. The higher risk of thromboembolic and bleeding events in the group of patients who received dabigatran compared with warfarin reinforced current guidelines recommending against the use of TSOACs in patients with mechanical heart valves. However, additional studies are needed to find suitable alternatives to vitamin K antagonists in this unique patient population.

Thromboembolism in a patient with a mechanical mitral valve during anticoagulation with dabigatran etexilate

Recently, several new anticoagulants have been used instead of warfarin for preventing thromboembolism. In the RE-LY (Randomized Evaluation of Long-Term Anticoagulation Therapy) trial, the direct thrombin inhibitor dabigatran etexilate was as an effective and safe as dose-adjusted warfarin for prevention of stroke in high-risk patients with atrial fibrillation. However, the safety and efficacy of thromboprophylaxis after mechanical valve replacement is uncertain. We report a 57-year-old man with a mechanical heart valve who experienced acute upper limb thromboembolism during dabigatran intake. Dabigatran might be inadequate for thromboprophylaxis after mechanical valve replacement.

Mitral valve prosthesis choice for patients aged 65 years and over in the UK. Are the guidelines being followed and does it matter?

OBJECTIVE

Current guidelines recommend that most patients aged ≥65 years should undergo mitral valve replacement (MVR) using a biological prosthesis. The objectives of this study were to assess whether these guidelines are being followed in UK practice, and to investigate whether the guidelines are appropriate based on in-hospital mortality and mid-term survival.

METHODS

Data from the National Institute for Cardiovascular Outcomes Research Adult Cardiac Surgery Audit database from all National Health Service (NHS) hospitals and some private hospitals performing adult cardiac surgery in the UK between April 2001 and March 2011 were analysed. The overall cohort included 3862 patients aged ≥65 years who underwent first-time MVR. Propensity score matching and regression adjustment were used to compare outcomes between prosthesis groups.

RESULTS

The mean age was 73.0 years (SD 4.9) with 50% of patients having surgery with a mechanical prosthesis. This proportion decreased over the study period and with increasing patient age with marked variation between hospitals. In the propensity-matched cohort, in-hospital mortality in the biological group was 6.9%, and in the mechanical group it was 5.9% giving an unadjusted OR of 1.17 (95% CI 0.84 to 1.63). There was no significant difference in mid-term survival between the matched groups with an unadjusted HR for biological prosthesis of 1.08 (95% CI 0.93 to 1.24). Similar results were found when using regression adjustment on unmatched data.

CONCLUSIONS

Current guidelines concerning age and mitral valve prosthesis choice are not being followed for patients aged ≥65 years. With regards to in-hospital and mid-term mortality, this study demonstrates that there is no difference between prosthesis types.

[Dabigatran: transforming the management of oral anticoagulation]

The utility of oral anticoagulation with warfarin in thromboembolic disease has been demonstrated for several decades, although these drugs have significant problems in terms of adequate control, interactions and risk of bleeding. In the last decade, new anticoagulants have emerged. The first was dabigatran with a demonstrated anticoagulant effect approaching the ideal anticoagulant profile. The view that dabigatran transforms oral anticoagulation therapy has arisen from the RE-VOLUTION program, with more than 34000 patients analyzed. This program has confirmed the value of oral anticoagulation with dabigatran compared with other anticoagulants; this drug eliminates all the drawbacks of warfarin, benefitting both patients and the healthcare system. The growth of the aging population has increased the number of risk situations in which anticoagulation is used. There is now a drug that meets the criteria for the ideal anticoagulant, transforming the management of oral anticoagulation. The findings demonstrated with dabigatran in prior studies are progressively being transferred to clinical practice. Following the usual development of new drugs, and according to the latest Laurence Desmond stages, results in agreement with those of previous studies are expected, namely, indisputable improvements in oral anticoagulation for patients and the health system.

Anticoagulation for prosthetic valves

Implantation of prosthetic valve requires consideration for anticoagulation. The current guideline recommends warfarin on all mechanical valves. Dabigatran is the new generation anticoagulation medication which is taken orally and does not require frequent monitoring. This drug is approved for treatment for atrial fibrillation and venous thromboembolism, but the latest large trial showed that this drug increases adverse events when used for mechanical valve anticoagulation. On-X valve is the new generation mechanical valve which is considered to require less anticoagulation due to its flow dynamics. The latest study showed that lower anticoagulation level lowers the incidence of bleeding, while the risk of thromboembolism and thrombosis remained the same. Anticoagulation poses dilemma in cases such as pregnancy and major bleeding event. During pregnancy, warfarin can be continued throughout pregnancy and switched to heparin derivative during 6-12 weeks and >36 weeks of gestation. Warfarin can be safely started after 1-2 weeks of discontinuation following major bleeding episode.

Fatal association of mechanical valve thrombosis with dabigatran: a report of two cases

Several new oral anticoagulants have been approved for thromboembolism prevention in patients with nonvalvular atrial fibrillation. However, they are not yet approved for anticoagulation use in patients with prosthetic mechanical valves, and no randomized data have been published so far on their safety of use in these patients. We present two cases of patients with prosthetic mechanical mitral valves who were switched from warfarin and acenocoumarol to dabigatran and within 1 month experienced severe valve complications resulting in death. One patient experienced stroke and later cardiogenic shock and death, and the other experienced pulmonary edema, cardiogenic shock, and subsequent death.

Dabigatran versus warfarin in patients with mechanical heart valves

BACKGROUND

Dabigatran is an oral direct thrombin inhibitor that has been shown to be an effective alternative to warfarin in patients with atrial fibrillation. We evaluated the use of dabigatran in patients with mechanical heart valves.

METHODS

In this phase 2 dose-validation study, we studied two populations of patients: those who had undergone aortic- or mitral-valve replacement within the past 7 days and those who had undergone such replacement at least 3 months earlier. Patients were randomly assigned in a 2:1 ratio to receive either dabigatran or warfarin. The selection of the initial dabigatran dose (150, 220, or 300 mg twice daily) was based on kidney function. Doses were adjusted to obtain a trough plasma level of at least 50 ng per milliliter. The warfarin dose was adjusted to obtain an international normalized ratio of 2 to 3 or 2.5 to 3.5 on the basis of thromboembolic risk. The primary end point was the trough plasma level of dabigatran.

RESULTS

The trial was terminated prematurely after the enrollment of 252 patients because of an excess of thromboembolic and bleeding events among patients in the dabigatran group. In the as-treated analysis, dose adjustment or discontinuation of dabigatran was required in 52 of 162 patients (32%). Ischemic or unspecified stroke occurred in 9 patients (5%) in the dabigatran group and in no patients in the warfarin group; major bleeding occurred in 7 patients (4%) and 2 patients (2%), respectively. All patients with major bleeding had pericardial bleeding.

CONCLUSIONS

The use of dabigatran in patients with mechanical heart valves was associated with increased rates of thromboembolic and bleeding complications, as compared with warfarin, thus showing no benefit and an excess risk. (Funded by Boehringer Ingelheim; ClinicalTrials.gov numbers, NCT01452347 and NCT01505881.).

Differential profiles of thrombin inhibitors (heparin, hirudin, bivalirudin, and dabigatran) in the thrombin generation assay and thromboelastography in vitro

Thrombin is a central enzyme in hemostasis and thrombosis, and a proven target for anticoagulant therapies. We compared four marketed and representative thrombin inhibitors, heparin, hirudin, bivalirudin, and dabigatran, in in-vitro spike-in assays that covered their therapeutic ranges. The assays employed were low tissue factor (1 pmol/l)-triggered thrombin generation assay (TGA) with plasma and 1:8000 Recombiplastin-triggered thromboelastography (TEG) with whole blood, with or without tissue plasminogen activator (tPA)-induced fibrinolysis. The three direct thrombin inhibitors (DTIs) prolonged TGA lag time and TEG clotting time (R) with a potency stack-ranking of hirudin>dabigatran approximately equal to bivalirudin. Heparin had the most steep concentration-response curve for both parameters. In TGA, 1-2 μmol/l dabigatran or hirudin resulted in complete inhibition on peak, slope, and endogenous thrombin potential, whereas bivalirudin had no effect on these parameters up to 10 μmol/l. All three DTIs, but not heparin, displayed a paradoxical increase in peak and slope in the low concentration range. In TEG, whereas all four agents reduced clot strength (maximal amplitude) in synergy with tPA, hirudin was the only DTI that reduced maximal amplitude appreciably without tPA. Dabigatran had the strongest potentiating effect on tPA-induced fibrinolytic activity (Ly30). With regard to the effects on coagulation and clot strength (lag time, R, and maximal amplitude) in the respective therapeutic range, dabigatran elicited the most modest changes. In summary, our observations highlight the distinct features of each agent in thrombin generation, coagulation, and fibrinolysis. The contrasts between the agents are consistent with their known properties and are informative on efforts to define the optimal profiles of new anticoagulants.

Clinical strategies for selecting oral anticoagulants in patients with atrial fibrillation

Atrial fibrillation is a common arrhythmia. One of the important aspects of the management of atrial fibrillation is stroke prevention. Warfarin has been the longstanding anticoagulant used for stroke prevention in patients with atrial fibrillation. There are now three novel oral anticoagulants, which have been studied in randomized controlled trials and subsequently approved by the Federal Drug Administration for stroke prevention in patients with atrial fibrillation. Special patient populations, including renal insufficiency, elderly, prior stroke, and extreme body weights, were represented to varying degrees in the clinical trials of the novel oral anticoagulants. Furthermore, there is variation in the pharmacokinetics and pharmacodynamics of each anticoagulant, which affect the patient populations differently. Patients and clinicians are faced with the task of selecting among the available anticoagulants, and this review is designed to be a tool for clinical decision-making.

Newer oral anticoagulant agents: a new era in medicine

After a gap of almost 60 years following the development of warfarin, 2 new categories of oral anticoagulant agents have been approved for clinical use – the direct thrombin inhibitors and factor Xa inhibitors. These agents promise to be more convenient to administer with fixed dosing but still have equivalent efficacy and improved bleeding risk compared to warfarin. The clinical community is looking forward to the widespread usage of these agents but there is also some apprehension regarding bleeding risks, non-availability of specific reversal strategies and lack of specific monitoring parameters. This review article will attempt to educate the reader about three representative drugs from these classes: Dabigatran, Rivaroxaban and Apixaban. We will discuss the historical perspective to the development of these drugs, available research data and pharmacology of these agents. The best strategies for monitoring and reversal of these drugs in special situations will also be touched upon.

The discovery of dabigatran etexilate

Thromboembolic disease is a major cause of mortality and morbidity in the developed world and is caused by an excessive stimulation of coagulation. Thrombin is a key serine protease in the coagulation cascade and numerous efforts have been made to develop safe and effective orally active direct thrombin inhibitors (DTIs). Current anticoagulant therapy includes the use of indirect thrombin inhibitors (e.g., heparins, low-molecular-weight-heparins) and vitamin K antagonists such as warfarin. However there are several caveats in the clinical use of these agents including narrow therapeutic window, parenteral delivery, and food- and drug-drug interactions. Dabigatran is a synthetic, reversible DTI with high affinity and specificity for its target binding both free and clot-bound thrombin, and offers a favorable pharmacokinetic profile. Large randomized clinical trials have demonstrated that dabigatran provides comparable or superior thromboprophylaxis in multiple thromboembolic disease indications compared to standard of care. This minireview will highlight the discovery and development of dabigatran, the first in a class of new oral anticoagulant agents to be licensed worldwide for the prevention of thromboembolism in the setting of orthopedic surgery and stroke prevent in atrial fibrillation.

Over the next hill

In the tradition of Dr Arom, who had many interests in his clinical and research career, I will touch on three things that will impact the practice of clinical cardiac surgery over the next several years: use of bilateral internal mammary arteries, use of external mesh support to improve saphenous vein graft patency, and anticoagulation of mechanical heart valves. The remainder of the presentation goes into depth on the development of a bloodless heart surgery program, which is contemporary and timely as it encompasses some thoughts of this society.

New anticoagulants: A concise review

During the last 2 years, two new oral anticoagulants, dabigatran and rivaroxaban, have been approved in the United States. Phase II and Phase III clinical trials of dabigatran, rivaroxaban, and apixaban are summarized. Approach to perioperative management depends on the half-life of the medication, risk of surgical bleeding, and the patient's renal function. No reversal agent is available for any of the new oral anticoagulants. Management of bleeding patients is based on local measures and consideration of antifibrinolytic therapy and activated factor VII or prothrombin complex concentrate infusion based on healthy volunteer and animal studies. The new oral anticoagulants provide additional options to prevent venous thromboembolism in patients after orthopedic surgery or stroke in patients with atrial fibrillation but present unique challenges compared to warfarin.

Cost-effectiveness of mitral valve repair versus replacement by biologic or mechanical prosthesis

BACKGROUND

Surgical treatment strategies for mitral valve disease have progressively shifted toward repair given the better survival outcomes with this type of intervention. However, valve repairs and valve replacement may require reoperations with time. In the absence of clinical trials assessing the effectiveness of various mitral surgical treatments with time, we propose to develop cost-effectiveness models to compare sequential treatment strategies.

METHODS

Three simulation models were carried out to assess the cost-effectiveness of mitral valve repair as first-line treatment, compared with either mechanical or biologic valve replacements. Efficacy data were derived from both the published literature and from a specific clinical cohort of 582 patients treated for this condition. Using the French public health care system perspective, relevant direct costs were derived using a local resource utilization assessment and official costing data sources.

RESULTS

Over 10 years, costs per success were significantly lower (p < 0.01) for the mitral valve repair strategy versus biologic or mechanical valve replacements (€35,550, €49,492, and €54,634 per success, respectively). Over 20 years, costs per success were significantly lower (p < 0.01) for the mechanical valve replacement strategy compared with the mitral valve repair and biologic valve replacement (€94,763, €100,053, and €147,484 per success, respectively).

CONCLUSIONS

Considering the increased referral rate in older patients with degenerative mitral valve disease, and their shorter life expectancy, these results show that when medically required and technically practicable, mitral valve repair should be considered as the first-line strategy.