Objective: To identify those patients with nonrheumatic atrial fibrillation who are at high risk and those at low risk for arterial thromboembolism.
Design: Cohort study of patients assigned to placebo in a randomized clinical trial.
Setting: Five hundred sixty-eight inpatients and outpatients with nonrheumatic atrial fibrillation assigned to placebo therapy at 15 U.S. medical centers from 1987 to 1989 in the Stroke Prevention in Atrial Fibrillation study. Patients were followed for a mean of 1.3 years.
Measurements: Clinical variables were assessed at study entry and correlated with subsequent ischemic stroke and systemic embolism by multivariate analysis.
Main results: Recent (within 3 months) congestive heart failure, a history of hypertension, and previous arterial thromboembolism were each significantly and independently associated with a substantial risk for thromboembolism (greater than 7% per year; P less than or equal to 0.05). The presence of these three independent clinical predictors (recent congestive heart failure, history of hypertension, previous thromboembolism of 2.5% per year (no risk factors), 7.2% per year (one risk factor), and 17.6% per year (two or three risk factors). Nondiabetic patients without these risk factors, comprising 38% of the cohort, had a low risk for thromboembolism (1.4% per year; 95% Cl, 0.05% to 3.7%). Patients without clinical risk factors who were under 60 years of age had no thromboembolic events.
Conclusion: Patients with atrial fibrillation at high risk (greater than 7% per year) and low risk (less than 3% per year) for thromboembolism can be identified by readily available clinical variables.