Patients With Nonvalvular Atrial Fibrillation at Low Risk of Stroke During Treatment With Aspirin: Stroke Prevention in Atrial Fibrillation III Study

Abstract

Context.—Nonvalvular atrial fibrillation (AF) carries an increased risk for stroke, but absolute rates of stroke vary widely within the broad spectrum of AF patients.Objective.—To prospectively validate a risk stratification scheme identifying patients with AF with low rates of stroke when given aspirin.Design.—Prospective cohort study with mean duration of follow-up of 2.0 years, conducted between 1993 and 1997.Setting.—Outpatient clinics affiliated with academic medical centers.Patients.—Patients with AF categorized as "low risk" based on the absence of 4 prespecified thromboembolic risk factors: recent congestive heart failure or left ventricular fractional shortening of 25% or less, previous thromboembolism, systolic blood pressure greater than 160 mm Hg, or female sex at age older than 75 years.Intervention.—All participants given aspirin, 325 mg/d.Main Outcome Measures.—Ischemic stroke (considered disabling when Rankin score was II or worse 1-3 months later) and systemic embolism (primary events).Results.—Among 892 participants, the mean (SD) age was 67 (10) years, 78% were men, and histories of hypertension, diabetes, and ischemic heart disease were present in 46%, 13%, and 16%, respectively. The rate of primary events was 2.2% per year (95% confidence interval [CI], 1.6%-3.0%), of ischemic stroke was 2.0% per year (95% CI, 1.5%-2.8%), and of disabling ischemic strokes was 0.8% per year (95% CI, 0.5%-1.3%). Those with a history of hypertension had a higher rate of primary events (3.6% per year) than those with no history of hypertension (1.1% per year) (P<.001). The rate of disabling ischemic stroke was low in those with and without a history of hypertension (1.4% per year and 0.5% per year, respectively). The rate of major bleeding during aspirin therapy was 0.5% per year.Conclusion.—Patients with AF who have relatively low rates of ischemic stroke, particularly disabling stroke, during treatment with aspirin can be reliably identified.