Higher-Than-Usual Target International Normalized Ratio (INR) Range Required With On-X Aortic Valve Secondary to Recurrent Thromboembolic Strokes: A Case Report

Although the On-X aortic valve (AO) is considered less thrombogenic compared to its counterparts, we present a case where recurrent thromboembolic ischemic stroke occurred, first with a sub-therapeutic, then even with an elevated International Normalized Ratio (INR). A 36-year-old male, the background of On-X AO replacement but no other risk factors, developed thromboembolic stroke twice while on Warfarin, first with INR 1.4, second with INR 2.4. Despite extensive investigation, other than elevated levels of low-density lipoproteins, no other treatable cause was found with the latter episode. The INR range was increased to 2.5-3.5, and aspirin and statin were added. The occurrence of thromboembolic stroke with an On-X AO despite maintaining an INR of 2.4, presents a dilemma for future prevention. The American Heart Association (AHA) and the American College of Cardiology (ACC) guidelines for thromboembolism prevention in case of an On-X AO recommend an INR range of 1.5-2 as being effective when warfarin is used along with aspirin. The take-home message is that the recommendation of an INR range of 1.5-2 with an On-X AO should be approached with caution; aspirin should be strongly considered regardless of the presence of thromboembolic risk factors. Patients developing thromboembolism have a high risk of recurrence. Therefore, a higher INR, along with the addition of aspirin and statin should be considered. Studies are needed to establish guidelines for a reliable INR range in these scenarios.