Boston Area Anticoagulation Trial for Atrial Fibrillation (1990)


Prevention of stroke in chronic non-valvular AF

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To assess the efficacy of low-dose warfarin for primary stroke prevention in patients with AF

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Trial design

Randomized, unblinded, controlled phase III study
Active treatment: low-dose warfarin (target range for the prothrombin-time ratio: 1.2–1.5 times the control; estimated INR equivalent 1.5–2.7) (n=212)
Control treatment: no treatment (n=208); ASA allowed, but not in the warfarin group

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Primary endpoint: ischemic stroke
Secondary endpoint: systemic emboli, major and minor bleeding, death

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Trial participants

420 patients (mean age 68 years), with chronic, sustained or intermittent non-valvular AF with no evidence of mitral stenosis on two-dimensional echocardiography

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Efficacy outcome: There were 2 ischemic strokes with warfarin (487 patient-years of observation; incidence 0.5% per year) as compared with 13 ischemic strokes in the control group (435 patient-years; incidence 3.0% per year) which corresponds to an 86% reduction in risk of stroke in the warfarin group. The overall death rate was markedly lower in the patients receiving warfarin than in the controls (2.2% vs. 6.0%)
Safety outcome: Major bleeding occurred in 2 patients of the warfarin group and in 1 patient of the control group. The rate of minor hemorrhage was higher with warfarin than in the controls (38 vs. 21 patients). The frequency of bleeding events that led to hospitalization or transfusion was essentially the same in both groups

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Efficacy: Low-dose warfarin is highly effective in preventing stroke in patients with AF. The risk reduction as compared to untreated controls (ASA allowed) was 86%
Safety: With careful monitoring the long-term low-dose warfarin therapy is safe. The total mortality rate was lower as compared to the control group

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The Boston Area Anticoagulation Trial for Atrial Fibrillation Investigators. The effect of low-dose warfarin on the risk of stroke in patients with non-rheumatic atrial fibrillation. N Engl J Med 1990;323:1505-1511

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Corresponding author

J. Philip Kistler, MD, Stroke Service, Massachusetts General Hospital, Boston MA 02114

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