Atrial fibrillation (AF) increases the risk of ischemic stroke five- to sevenfold because of left atrial thrombus formation and cerebral embolization. Prior to the Stroke Prevention in Atrial Fibrillation (SPAF) study, the efficacy of antithrombotic medications for stroke prevention in patients with AF and absence of cardiac valvular disease had not been firmly established, although smaller trials had suggested a benefit. SPAF was undertaken to evaluate the role of anticoagulant and antiplatelet therapies in a large population of these patients by comparing the outcomes of treatment with warfarin or aspirin compared to placebo.

To evaluate whether treatment with warfarin or aspirin is more effective for preventing ischemic stroke and systemic embolization compared to placebo in patients with nonvalvular AF.

Double-blind, placebo-controlled trial conducted at 15 clinical centers between 1987 and 1989.