Purpose of review: The goal of anticoagulation in patients with mechanical aortic valve replacement (AVR) is to maintain an optimal international normalized ratio (INR) that minimizes both the risk of bleeding and thromboembolic events. Here, we review the published data on anticoagulation with bileaflet mechanical prostheses, with a focus on the On-X valve (On-X Life Technologies, Austin, TX), which was designed to function with less anticoagulation or, in some cases, antiplatelet therapy only.
Recent findings: Several long-term follow-up studies with the On-X valve demonstrate low rates of bleeding and thromboembolism with standard and low-dose anticoagulation. The Prospective Randomized On-X Anticoagulation Clinical Trial (PROACT) compared the safety of less aggressive anticoagulation (INR 1.5-2.0) with standard anticoagulation (INR 2.0-3.0) after implantation of On-X aortic prostheses for patients at high risk of thromboembolic events. The updated 5-year data confirm that low-dose warfarin is associated with lower major bleeding (1.6 vs. 3.9%/patient-year; P = 0.007) with no difference in thromboembolic events (0.11 vs. 0.52%/patient-year; P = 0.2).
Summary: Nonrandomized studies and the PROACT data support the safety and efficacy of maintaining the On-X bileaflet mechanical aortic valve prosthesis at a lower target INR than current guideline recommendations for patients at high risk of thromboembolic events. These results offer the promise of a valve prosthesis with excellent durability combined with reduced anticoagulation-related complications.