Nonrheumatic atrial fibrillation. Risk of stroke and role of antithrombotic therapy.

T here has been a long-standing consensus1 that the risk of embolization in patients with atrial fibrillation and rheumatic heart disease, in particular, mitral stenosis, is sufficiently high to justify anticoagulant prophylaxis. However, there has been no consensus in regard to nonrheumatic atrial fibrillation. The recognition that nonrheumatic atrial fibrillation is common and associated with a high risk of systemic embolization and stroke, as well as the suggestion of reduced embolism from both nonrandomized trials of oral anticoagulation in atrial fibrillation and randomized trials of anticoagulant and antiplatelet drugs in vascular diseases, heightened awareness of the potential efficacy of antithrombotic therapy. This recognition, together with evidence of the greater safety of lower-dose warfarin, prompted the initiation of several randomized trials of anticoagulant and antiplatelet therapy of nonrheumatic atrial fibrillation. Some of these trials are now complete, and a review of antithrombotic therapy in nonrheumatic atrial fibrillation is timely. Many types of heart disease are associated with atrial fibrillation, including coronary artery disease, hypertension, congestive heart failure, and rheumatic heart disease. The incidence and outcome data from the Framingham Study2-6 distinguished rheumatic atrial fibrillation from atrial fibrillation unassociated with rheumatic heart disease. Most patients in recent studies of atrial fibrillation have had no evidence of rheumatic heart disease, and the term "nonrheumatic atrial fibrillation" has been widely adopted to describe the disorder in this group of patients.7-10 In