Boston Area Anticoagulation Trial for Atrial Fibrillation - BAATAF


Warfarin for ischemic stroke in atrial fibrillation.


The benefits of long-term warfarin therapy outweigh its risks and inconvenience.

Study Design

Study Design:

Patients Screened: Not given
Patients Enrolled: 420
Mean Follow Up: 2.2 years
Mean Patient Age: 68
Female: 28

Patient Populations:

Adults with chronic sustained or intermittent atrial fibrillation, with no evidence of mitral stenosis on 2-dimensional echocardiography (i.e., with "nonrheumatic" atrial fibrillation), as demonstrated on 2 separate electrocardiograms (ECGs).

If intermittent, atrial fibrillation must be documented by ECG within 18 months of entry.


Requirement for aspirin therapy.

Primary Endpoints:

Ischemic stroke, defined as sudden onset of a neurologic deficit fitting a cerebroarterial distribution and lasting 24 h or more, with no hemorrhage evident.

Secondary Endpoints:

Noncerebrovascular (i.e., peripheral systemic) thromboembolism.

Drug/Procedures Used:

Low-dose warfarin (target prothrombin-time ratio, 1.2 to 1.5).

Concomitant Medications:

Control group only: aspirin if desired

Principal Findings:

There were 15 ischemic strokes during the trial; one was fatal. 11 were judged to be embolic (2 in posterior circulation).

2 of the 15 strokes were in the warfarin group, 13 in the control group; the warfarin group had an 86% reduction of risk (control incidence ratio = 0.14; 95% confidence interval [CI] 0.04 to 0.49; p = 0.0022).

37 patients died. 19 deaths were from cardiac causes, 18 from other causes. The death rate was markedly lower in the warfarin group than in the control group (2.25% compared with 5.97% per year, for an incidence ratio of 0.38 [95% CI 0.17 to 0.82; p = 0.005]).

There was one fatal hemorrhage in each group.

The frequency of bleeding events that led to hospitalization or transfusion was essentially the same in both groups.

The warfarin group had a higher rate of minor hemorrhages than the control group (38 vs. 21 patients).

Simultaneously controlling for the other significant determinants of stroke in the BAATAF study (age, mitral annular calcification, and clinical heart disease), the relative rates (95% confidence interval) of stroke were: (1) warfarin/aspirin = 0.135 (0.029 to 0.64); (2) aspirin/(no aspirin and no warfarin) = 1.95 (0.64 to 5.97); and (3) warfarin/(no aspirin and no warfarin) = 0.263 (0.051 to 1.36).

No significant differences between warfarin-treated and control patients were found on well-validated measures of functional status, well-being, and health perceptions.

Incremental costs per life-year gained was calculated using efficacy data from the Boston Area Anticoagulation Trial for Atrial Fibrillation, a meta-analysis of 5 nonrheumatic atrial fibrillation trials, cost data from a district general hospital, and review of the literature. The cost per life-year gained free from stroke over 10 years ranged from £400.45 (ie, a resource saving achieved for each life-year gained free from stroke) to £13,221.29. The results were most sensitive to alteration in the frequency of anticoagulation monitoring.


Low-dose warfarin is effective for preventing stroke in patients with nonrheumatic atrial fibrillation. Analysis of patients who elected to take aspirin and those who elected no anticoagulant or antiplatelet therapy suggests that warfarin is more effective than aspirin in preventing stroke in nonrheumatic atrial fibrillation.


1. N Engl J Med 1990; 323:1505-1511 Design and baseline results
2. Arch of Int Med 1991; 151:1944-9 Quality of Life
3. Am Heart J 1992;124:1567-73 Aspirin analysis
4. Stroke 1998; 24:1360-5 Effect on F1+2 levels
5. Stroke 1998; 29(9):1827-32 Cost-effectiveness

Clinical Topics: Anticoagulation Management, Noninvasive Imaging, Valvular Heart Disease, Echocardiography/Ultrasound

Keywords: Stroke, Platelet Aggregation Inhibitors, Warfarin, Mitral Valve Stenosis, Prothrombin, Confidence Intervals, Electrocardiography, Echocardiography

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