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.