Stroke Prevention in Atrial Fibrillation (1991)


Prevention of stroke and systemic embolism in patients with AF

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To investigate the efficacy and safety of warfarin and ASA in the prevention of stroke and systemic embolism

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Trial design

Randomized, placebo-controlled trial
Active treatment:

  • Group 1 (627 patients eligible for oral anticoagulation): warfarin (INR 2.0–4.5) (n=210) or ASA (325 mg once daily)
  • Group 2 (703 patients ineligible for oral anticoagulation): ASA (n=346) or placebo (n=357)

Control treatment: placebo (group 1: n=211, group 2: n=357)

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Primary efficacy endpoint: ischemic stroke or systemic embolism
Secondary efficacy endpoints: death, myocardial infarction, TIA, or unstable angina pectoris requiring hospital admission
Primary safety endpoint: major hemorrhagic events

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Trial participants

1330 inpatients and outpatients with constant or intermittent AF

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Primary outcome: Mean follow-up was 1.3 years. In group 1, a primary event occurred in 6 of 210 patients (2.3% per year) receiving warfarin and in 18 of 211 (7.4% per year) placebo patients (relative risk reduction 67%). In group 2, 26 of 552 patients assigned to ASA (3.6% per year) and 46 of 568 patients assigned to placebo (6.3% per year) experienced a primary event (relative risk reduction 42%)
Safety outcome: In group 1, the risk of relevant bleeding was 1.5% (n=4) in patients given warfarin compared to 1.6% (n=4) in placebo patients. In group 2, 10 patients assigned to ASA (1.4%) experienced a relevant bleeding complication compared to 14 patients (1.9%) assigned to placebo

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Efficacy: Warfarin and ASA are both effective in reducing ischemic stroke and systemic embolism in patients with AF. Too few events occurred in warfarin-eligible patients to directly assess the relative benefit of ASA compared with warfarin
Safety: There were no significant differences in bleeding events between groups

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Cohen BA, Feldman G, Flaker GC, Hart RG, McAnulty JH, McBride R. Stroke Prevention in Atrial Fibrillation Study. Final results. Circulation 1991;84:527-539

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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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