Stroke Prevention in Atrial Fibrillation II study (1994)


Prevention of stroke and systemic embolism in patients with AF

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To compare the efficacy and safety of warfarin with ASA in the prevention of stroke and systemic embolism in two age-cohorts

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Trial design

Two parallel randomized controlled trials
Active treatment: warfarin (INR 2.0–4.5)
Control treatment: ASA (325 mg once daily)

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Primary efficacy endpoint: ischemic stroke or systemic embolism
Secondary efficacy endpoints: TIA, myocardial infarction, strokes with residual deficits, death
Primary safety endpoints: major hemorrhagic events, intracranial hemorrhage

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Trial participants

715 patients with AF aged 75 years or younger and 385 patients older than 75 years

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Efficacy outcome: In the younger patients, primary events occurred in 14 of 358 patients (1.3% per year) given warfarin and 21 of 357 patients (1.9% per year) given ASA (relative risk reduction 33%). In the older patient cohort, primary events were observed in 14 of 197 patients (3.6% per year) receiving warfarin and in 18 of 188 patients (4.8% per year) receiving ASA (relative risk reduction 27%)
Safety outcome: In the younger patient group rates of major hemorrhage were 1.7% per year with warfarin and 0.9% per year with ASA. For older patients, the rates were 4.2% (warfarin) and 1.6% per year (ASA). In older patients assigned to warfarin, the annual rate of intracranial hemorrhage was 1.8% (71% fatal, 29% with residual deficit) compared to 0.5% in younger patients assigned to warfarin

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Efficacy: Warfarin may be more effective than ASA in reducing ischemic stroke and systemic embolism in younger and older patients with AF. In older patients, the rate of stroke was substantial, irrespective of which agent was given
Safety: The risk of major bleeding and intracranial bleeding among anticoagulated patients ≤75 years was lower than in the older cohort (p=0.008, and p=0.05, respectively)

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Halperin JL, Hart RG, Kronmal RA, McBride R, Pearce LA, Sherman DG. Warfarin versus aspirin for prevention of thromboembolism in atrial fibrillation: Stroke Prevention in Atrial Fibrillation II Study. Lancet 1994;343:687-691

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Corresponding author

Ruth McBride, Statistics and Epidemiology Research Corporation, 1107 NE 45th Street, Suite 520, Seattle, WA 98105

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