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[Atrial fibrillation and thromboembolism: a multicenter cooperative study. Research Group for Antiarrhythmic Drug Therapy].

A multicenter, retrospective study was undertaken to determine the prevalence of and risk factors for thromboembolism and efficacy of therapy in patients with atrial fibrillation. The primary prevention group consisted of 1,819 Japanese patients (mean age 64 years). During the mean follow-up period of 4.6 years. 158 patients developed cerebral thromboembolism or peripheral embolism (1.9%/year). The annual rate of thromboembolic complications was 0.9% for patients without underlying heart disease which was significantly lower compared with that for patients with underlying heart disease (p < 0.001). The annual rate was 1.4% among patients treated with aspirin (alone and in combination with other drugs except for warfarin), 1.4% with warfarin (alone and in combination with other drugs) and 1.1% with ticlopidine. The risk was lower for patients receiving these drugs (2.2%/year, p < 0.001). Among 801 patients not receiving treatment for thromboembolism, the annual rate was 0.9% for patients without underlying heart disease, which was significantly lower compared with patients with underlying heart diseases (e.g., 2.5% for ischemic heart disease and 2.1% for mitral valve disease, p < 0.001). Multivariate analysis using quantification method II revealed hypertension, sick sinus syndrome and left ventricular dysfunction (> or = NYHA class II) as risk factors for embolism. Although limited due to its retrospective nature, the present study suggests that the risk for embolism seems low in patients with atrial fibrillation but is not associated with underlying heart diseases or other risk factors, and antiplatelet treatment seems beneficial for these patients.