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(Stroke. 2008;39:2736.)
© 2008 American Heart Association, Inc.

Original Contributions

Racial/Ethnic Differences in Ischemic Stroke Rates and the Efficacy of Warfarin Among Patients With Atrial Fibrillation

Albert Yuh-Jer Shen, MS, MD; Janis F. Yao, MS; Somjot S. Brar, MD; Michael B. Jorgensen, MD; Xunzhang Wang, MD Wansu Chen, MS

From Department of Research and Evaluation (J.F.Y., W.C.), Kaiser Permanente Medical Center, Pasadena, Calif; Center for Interventional Therapeutics (CIVT) (S.S.B.), Columbia University Medical Center, New York, NY; Department of Cardiology (A.Y.-J.S., M.B.J.), Department of Electrophysiology (M.B.J., X.W.), Kaiser Permanente Medical Center, Los Angeles, Calif.

Correspondence to Albert Yuh-Jer Shen, Department of Cardiology, Kaiser Permanente Medical Center, 1526 Edgemont St, 2nd floor, Los Angeles, CA 90027; E-mail albert.y-j.shen{at}kp.org

Background and Purpose— Warfarin reduces stroke risk in studies of predominantly white patients with atrial fibrillation (AF). Whether nonwhites also have lower rates of stroke while treated with warfarin is unclear.

Methods— A multiethnic stroke-free cohort hospitalized with nonrheumatic AF was identified in a large health maintenance organization. Stroke risk factors (advanced age, diabetes, hypertension, and heart failure), warfarin use, and anticoagulation intensity were assessed. Crude ischemic stroke rates were calculated by Poisson regression for each group while using and not using warfarin. Cox proportional hazard models were constructed to assess the independent effect of race/ethnicity on ischemic stroke.

Results— Between 1995 and 2000, we identified 18867 AF hospitalizations (78.5% white, 8% black, 9.5% Hispanic, and 3.9% Asian). Over the course of 63204 person-years follow-up (median, 3.3 years), 1226 ischemic strokes were identified. The percent-time on warfarin did not differ by race/ethnicity. The median percent-time on warfarin that international normalized ratio was 2 to 3 was 54.5% overall, but it was lower in blacks at 47.8%, whereas the other groups had a rate of 54%. The rate ratios (95% CI) of ischemic stroke with warfarin compared to without warfarin for whites, blacks, Hispanics, and Asians were 0.79 (0.68 to 0.90), 0.92 (0.65 to 1.30), 0.71 (0.48 to 1.05), and 0.65 (0.34 to 1.23), respectively.

Conclusions— In this cohort, we did not observe a statistically significant lower rate of stroke with warfarin therapy among nonwhites (in particular blacks) with previous AF hospitalizations. The relatively small numbers of nonwhites renders our estimates less than precise and should be interpreted with caution.

Key Words: atrial fibrillation • racial differences • stroke • warfarin