Sex Differences in Stroke Risk Among Older Patients With Recently Diagnosed Atrial Fibrillation

CONTEXT: Stroke is a serious complication associated with atrial fibrillation (AF). Women with AF are at higher risk of stroke compared with men. Reasons for this higher stroke risk in women remain unclear, although some studies suggest that undertreatment with warfarin may be a cause. OBJECTIVE: To compare utilization patterns of warfarin and the risk of subsequent stroke between older men and women with AF at the population level. DESIGN, SETTING, AND PATIENTS: Population-based cohort study of patients 65 years or older admitted to the hospital with recently diagnosed AF in the province of Quebec, Canada, 1998-2007, using administrative data with linkage between hospital discharge, physicians, and prescription drug claims databases. MAIN OUTCOME MEASURES: Risk of stroke. RESULTS: The cohort comprised 39,398 men (47.2%) and 44,115 women (52.8%). At admission, women were older and had a higher CHADS(2) (congestive heart failure, hypertension, age ≥75 years, diabetes mellitus, prior stroke or transient ischemic attack) score than men (1.99 [SD, 1.10] vs 1.74 [SD, 1.13], P < .001). At 30 days postdischarge, 58.2% of men and 60.6% of women had filled a warfarin prescription. In adjusted analysis, women appeared to fill more warfarin prescriptions compared with men (odds ratio, 1.07 [95% CI, 1.04-1.11]; P < .001). Adherence to warfarin treatment was good in both sexes. Crude stroke incidence was 2.02 per 100 person-years (95% CI, 1.95-2.10) in women vs 1.61 per 100 person-years (95% CI, 1.54-1.69) in men (P < .001). The sex difference was mainly driven by the population of patients 75 years or older. In multivariable Cox regression analysis, women had a higher risk of stroke than men (adjusted hazard ratio, 1.14 [95% CI, 1.07-1.22]; P < .001), even after adjusting for baseline comorbid conditions, individual components of the CHADS(2) score, and warfarin treatment. CONCLUSION: Among older patients admitted with recently diagnosed AF, the risk of stroke was greater in women than in men, regardless of warfarin use.