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Recommendations to prescribe long-term anticoagulation for patients with atrial fibrillation are based largely on estimates of the incidence of stroke and major hemorrhage. Investigators reviewed data from a California HMO on a cohort of 13,559 patients with nonvalvular atrial fibrillation (66,000 person-years of follow-up). Net clinical benefit was defined as the annual combined rate of ischemic stroke and systemic emboli that was prevented by warfarin, minus the annual rate of intracranial hemorrhages that were attributable to warfarin multiplied by 1.5 (the multiplier was included to give greater clinical weight to intracranial hemorrhage).
Net clinical benefit of warfarin, adjusted for stroke and hemorrhage risk factors, was 0.68% annual…