Low-Dose Warfarin with a Novel Mechanical Aortic Valve: Interim Registry Results at 5-Year Follow-Up

Objective(s) To evaluate whether warfarin targeted at an international normalized ratio of 1.8 (range 1.5-2.0) following On-X mechanical aortic valve implant is safe for all patients. Methods This prospective, observational clinical registry assessed adverse event rates in adult patients receiving low-dose warfarin (target international normalized ratio 1.8, range 1.5-2.0) plus daily aspirin (75-100 milligrams) during a 5-year period following On-X aortic valve implant. The primary endpoint is the combined rate of major bleeding, valve thrombosis, and thromboembolism overall and in 4 subgroups. The comparator is the Prospective Randomized On-X Anticoagulation Trial control group patients on standard-dose warfarin (international normalized ratio 2.0-3.0) plus aspirin 81 milligrams daily. Results A total of 510 patients were recruited at 23 centers in the United States, United Kingdom, and Canada between November 2015 and January 2022. This interim analysis includes 229 patients scheduled to complete 5-year follow-up by August 16, 2023. The linearized occurrence rate (in percent per patient-year) of the primary composite endpoint of major bleeding, valve thrombosis, and thromboembolism is 1.83% compared with 5.39% (95% confidence interval 4.12%-6.93%) in the comparator group. Results are consistent in clinic-monitored and home-monitored patients and in those at high risk for thromboembolism. Major bleeding and total bleeding were reduced by 87% and 71%, respectively, versus the comparator group, without an increase in thromboembolic events. Conclusions Interim results support the continued safety of the On-X aortic mechanical valve with a target international normalized ratio of 1.8 plus low-dose aspirin through 5 years post-implant, with or without home monitoring.