Major Bleeding and Thromboembolic Events with the On-X Mechanical Aortic Valve Prosthesis: A SWEDEHEART Study

OBJECTIVES: Lifelong anticoagulation therapy is mandatory in patients with mechanical heart valves. The On-X aortic valve is currently the only mechanical heart valve approved for a lower (1.5-2.0) target international normalized ratio (INR) compared to the standard INR target 2.0-3.0. There is limited evidence demonstrating clinical benefits of the On-X valve over other mechanical aortic valves. We therefore investigated the risk of bleeding and thromboembolic events in patients with the On-X aortic valve. METHODS: This nationwide, population-based cohort study, using the target trial emulation framework, included all adults who underwent primary mechanical aortic valve replacement in Sweden 2014-2022 from the SWEDEHEART register. The rates of major bleeding and thromboembolic events were obtained from national registers. Confounding was addressed by weighting. RESULTS: Of the 3047 patients, 656 patients (22%) received an On-X aortic valve and 2391 patients (78%) received other mechanical aortic valves. The mean age was 54 years and 23% were women. After 8 years, the weighted major bleeding cumulative incidence was 7.2% (95% CI: 4.8%-10.7%) in the On-X valve group vs 7.0% (95% CI: 5.5%-8.8%) in the other mechanical valves group, and the weighted cumulative incidence of thromboembolic events was 7.3% (95% CI: 5.3%-10.2%) in the On-X valve group vs 6.4% (95% CI: 5.0%-7.9%) in the other mechanical valves group. CONCLUSIONS: We found no clinically relevant difference in major bleeding or thromboembolic events in patients with the On-X aortic valve compared to patients with other mechanical aortic valves.