Relationship of international normalized ratio to bleeding and thromboembolism rates in Taiwanese patients receiving vitamin K antagonist after mechanical valve replacement.

Abstract

Asians may be less vulnerable to thrombotic disease than Caucasians. Optimum international normalized ratio (INR) anticoagulant therapy guidelines for Asian populations remain to be established. This study investigated the risk factors for major bleeding or thromboembolism (TE) in Taiwanese patients receiving mechanical aortic and/or mitral valve replacement, including INR < or > 2.0. The records of 563 Taiwanese patients receiving mechanical aortic and/or mitral valve replacement between 1996 and 2001 were retrospectively studied. Patient follow-up data was divided into several 6-month periods: 6-month increments after surgery if no bleeding or TE occurred and the 6 months preceding the adverse event when an event occurred. Data including warfarin sodium dosage and estimated INR unit for each time period were collected and analyzed. A total of 3,391 records were retrieved for analysis with an average follow-up period of 3.3 +/- 1.4 years. The mean warfarin sodium dose was 2.86 +/- 1.09 mg/day and the INR was 1.86 +/- 0.66. Major bleeding events occurred in 20 patients (1.07% per patient-year) and TE events in 38 patients (2.04% per patient-year), accounting for a 3.11% rate of overall events (bleeding or TE) per patient-year. Multivariate risk analysis revealed follow-up age > 60 years and receiving mitral valve replacement were risk factors for overall events (odds ratio = 1.84, p = 0.021 for follow-up age > 60 years; odds ratio = 1.36, p = 0.019 for receiving mitral valve replacement), while gender, double valve replacement, valve type, INR < 2.0, and atrial fibrillation were not. Our data suggest that low-intensity anticoagulant therapy (INR < 2.0) in Taiwanese patients was not associated with increased TE and bleeding rates compared to higher intensity anticoagulant therapy. Follow-up age over 60 years and valve replacement at the mitral site were associated with increased rate of overall events.