Preventing stroke in patients with atrial fibrillation.

CONTEXT: Atrial fibrillation, a common disorder that affects nearly one sixth of the population aged 75 years and older, is a major risk factor for stroke.
OBJECTIVES: To review and evaluate the evidence supporting the use of warfarin and/or aspirin for stroke prevention in patients with atrial fibrillation. DATA SOURCES: Prospective, randomized trials of patients with atrial fibrillation evaluating either warfarin or aspirin or both, from MEDLINE from January 1, 1966, to February 23, 1999. STUDY SELECTION: Five primary prevention placebo-controlled studies, which had been formally pooled, 1 study evaluating secondary prevention of stroke, 1 study comparing warfarin with aspirin, and 3 studies of warfarin in combination with aspirin were identified. DATA SYNTHESIS: The risk of developing stroke is heterogeneous and increases with each decade above 65 years; history of high blood pressure, diabetes mellitus, previous transient ischemic attack, or stroke; poor ventricular function; and in women older than 75 years. For patients younger than 65 years, without risk factors, and not receiving antithrombotic therapy, the risk of stroke is 1%/y; those without risk factors between the ages of 65 and 75 years have a risk of 1.1%/y if taking warfarin and 1.4%/y if taking aspirin. For all other patients, stroke risk is reduced from an untreated rate of between 4.3%/y and more than 12%/y to a rate of 1.2%/y to 4%/y with warfarin use.
CONCLUSION: The protection afforded by warfarin is most pronounced in patients at the highest risk for stroke, while aspirin treatment seems adequate in low-risk populations.