Review of anticoagulation options for mechanical valve prosthesis

Abstract

Clinical guidelines recommend lifelong oral anticoagulation (OAC) with warfarin in all patients with mechanical valves with variance in the target INR for patient associated risk factors, type of mechanical valve or implant position of the valve. Recent randomized controlled trials have demonstrated that clinicians may consider a lower OAC strategy (INR: 1.5-2.5) in low (thrombogenic) risk patients undergoing bileaflet mechanical valve replacement thereby achieving similar thromboprophylaxis yet minimizing bleeding events. Likewise, physicians may also consider a lowered OAC option in high (thrombogenic) risk patients undergoing bileaflet mechanical valve replacement yielding similar efficacy (avoidance of thromboembolic events) and improving safety (bleeding events). Finally, while advancement of novel oral anticoagulants (NOACs) has been swift in the realm of atrial fibrillation anticoagulation management, NOACs for mechanical valves are currently contraindicated due to evidence of increased thromboembolic and bleeding risk. Future studies comparing NOACs and warfarin along with newer mechanical valve construction are eagerly being awaited. a significant increased risk of major bleeding [16]. At mid-term follow-up, contemporary (2005+) incidence of thromboembolic events has been relatively low ranging from 0 to 3.6% [17,18]. With the advent of newer generation mechanical valves, there is potential for achieving even lower rates of thromboembolic and bleeding events with either less intense OAC, antiplatelet therapy alone or potentially novel OACs (NOAC). Therefore, this review is aimed at discussing current practice trends, novel strategies and future endeavors for postoperative t hromboprophylaxis for mechanical valves. Current practice for anticoagulationCurrent international guidelines generally recommend the following: low dose aspirin (74-100 mg) for all patients, OAC in mechanical aortic valves with target INR 2.0-3.0 at low-risk for thromboembolic events and OAC with target INR 2.5-3.5 in mechanical mitral valves and high-risk aortic valve patients (Table 1) [12][13][19][20]. High-risk patients are considered to be those with concomitant atrial fibrillation, previous thromboembolism, hypercoagulable state or depressed left ventricular function [21,22]. These recommendations have been partially based on older studies using more thrombogenic mechanical valves (i.e., StarrEdwards ball and cage, Bjork-Shiley tilting disc) [23][24][25] along with a landmark meta-analysis by Cannegieter and colleagues [20]. Moreover, based on Massel and Little's meta-analysis, the European guidelines advise caution with the addition of an antiplatelet medication due to the increased risk of bleeding with an odds ratio of 1.58 (95% CI: 1.14-2.18) [16,26]. Several groups have demonstrated similar effectiveness with reduced OAC therapy (compared with historically target INR of 3.0-4.5 in patients with bileaflet St. Jude Medical [St. Jude Medical, Inc., Saint Paul, MN, USA]) mechanical valves, mostly in the aortic position [21,27]...