Adequate intensity of warfarin therapy for Korean patients with mechanical cardiac valves

The study aim was to identify adequate therapeutic ranges of the International Normalized Ratio (INR) in Korean patients receiving warfarin after prosthetic mechanical heart valve replacement.

Retrospective chart reviews were conducted of 818 patients for a total follow up period of 8,100 patient-years; all details of major complication events of thromboembolism and bleeding were recorded. The INR-incidence of complication curve was plotted, and an adequate INR determined from the intersections of 95% confidence interval (CI) curves of complication rates to ensure the lowest incidences of both thromboembolic and bleeding complications. An analysis of a subgroup of patients with atrial fibrillation (AF) was performed to evaluate the complication occurrence.

A total of 69 complications occurred, of which 36 were thromboembolic events and 33 were bleeding. The adequate ranges of INR were determined as: 2.0-2.5 for patients with aortic or mitral valve replacement; 2.1-2.6 for those with aortic plus mitral valve replacement; and 2.3-2.8 for those with tricuspid valve replacement with or without other valves. It has been shown that, by keeping the INR levels within these therapeutic ranges, complication risks could be significantly reduced by up to 51%. The overall incidence of complications was increased if the patients had AF (hazards risk (HR) = 1.27, 95% CI = 1.05-1.52).

The study results may provide evidence for the application of low-intensity warfarin therapies in Asian patients, including Koreans. In addition, the method of determining adequate INR levels by using INR-incidence of complications curves might be employed in many clinical settings.