Optimal INR to Prevent Stroke in Thai Patients with
Rheumatic Mitral Stenosis and Atrial Fibrillation Who are
Receiving Warfarin
Kaewkanlaya R, MD¹, Chokesuwattanaskul R, MD¹, Songmuang SB, MD¹
Affiliation : ¹ Division of Cardiology, Department of Medicine. Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
Objective: To determine the optimal international normalized ratio (INR) level to prevent stroke and bleeding in patients with
rheumatic mitral stenosis and atrial fibrillation (AF) receiving warfarin.
Materials and Methods: The present study was a retrospective study that enrolled patients with rheumatic mitral stenosis and AF who received warfarin at King Chulalongkorn Memorial Hospital between January 1, 2010 and December 31, 2015. The INR range was classified into six groups, which were less than 1.50, 1.50 to 1.99, 2.00 to 2.49, 2.50 to 2.99, 3.00 to 3.49 and 3.50 and more.
Results: One hundred eighty-four patients (mean age of 55.7 years, 79.3% female) were enrolled, for a follow-up of 714.4 patient- year. Twenty-eight patients had 35 ischemic stroke events (4.90 per 100 patient-years) and 36 patients had 55 bleeding events (7.70 per 100 patient-years). The time rate in the INR range of less than 1.50, 1.50 to 1.99, 2.00 to 2.49, 2.50 to 2.99, 3.00 to 3.49 and 3.50 and more were 14.0%, 26.7%, 29.5%, 17.4%, 7.1%, and 5.2%, respectively. The percentage of patient-time spent within INR range 2 to 3, INR less than 2, and INR more than 3 were 46.9%, 40.7%, and 12.3%, respectively. The INR level less than 2.00 increased the incidence rate of ischemic stroke (relative risk [RR] 1.57; 95% confidence interval [CI] 1.19 to 2.13; p=0.028). The INR level more than 2.99 to 3.5 increased the incidence rate of total and major bleeding events (RR 2.47; 95% CI 1.88 to 3.23; p<0.001 and RR 3.07; 95% CI 2.44 to 3.87; p<0.001, respectively). The overall of ischemic stroke and bleeding event rate was lowest in the INR range from 2.00 to 2.99.
Conclusion: In this large cohort of patients with rheumatic mitral stenosis and AF, an INR level between 2.00 to 2.99 was associated with the lowest incidence of ischemic stroke and bleeding. This optimal INR level is higher than the optimal INR as previously shown in other studies of Asian patients with non-valvular AF.
Keywords : Atrial fibrillation, Rheumatic mitral stenosis, INR, Stroke, Warfarin
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