Boston Area Anticoagulation Trial for Atrial Fibrillation (BAATAF)


Phase 3 Results

Trial Description

To determine the benefits and risks of oral anticoagulant therapy in reducing embolic stroke and systemic emboli in patients with atrial fibrillation without rheumatic heart disease.

Detailed Description

The efficacy of oral anticoagulation therapy in reducing the risk of embolic stroke in patients with atrial fibrillation and rheumatic heart disease was well known. The value of anticoagulant therapy in patients with atrial fibrillation without rheumatic heart disease had not been established. Several studies strongly suggested that although the risk of stroke in patients with atrial fibrillation was greatest in the presence of valvular disease, the risk of stroke in the absence of valvular disease was also much greater in patients with atrial fibrillation than those without this arrhythmia. What was lacking was a detailed controlled study assessing the degree of reduction in stroke risk by anticoagulation of fibrillating patients without valvular disease.
The second question asked was whether the added potential morbidity or mortality associated with long-term anticoagulation therapy justified its use in the prophylactic treatment of neurologically asymptomatic patients with atrial fibrillation, even if it did reduce stroke risk. Gastrointestinal, urinary tract, cutaneous and joint hemorrhages were all potential serious complications, as was cerebral hemorrhage, including bleeding into areas of recent cerebral infarction. Interest had again focused on hemorrhagic complications of stroke in anticoagulated patients and among risk factors for hemorrhage were large, recent infarcts. No one suggested that anticoagulation, even if very successful in reducing stroke risk, would eliminate it altogether, and thus hemorrhagic infarction was an important potential problem, as was assessment of risk of primary intracerebral hemorrhage.
Randomized non-blind. Recruitment began in September 1985 and ended in June 1989. The experimental group of 212 patients received long-term, low-dose warfarin. The control group of 208 patients did not receive warfarin but could choose to take aspirin. Average follow-up was 2.2 years. The primary endpoint was non-hemorrhage stroke. At entry and annually, the history was recorded and patients underwent a physical examination focusing on neurologic factors. Every year, beginning at six months, patients were sent a questionnaire on neurologic symptoms, bleeding episodes, and other medical conditions. Study nurses contacted all patients to review their responses. Each patient's referring physician was contacted at three months and nine months during each year of follow-up.
Participating institutions in the multicenter trial were organized into three groups. At Group I institutions, on-site investigators performed all clinical evaluations. In Group II, personnel from the central site hospital, the Massachusetts General Hospital, traveled to the local hospitals to evaluate, randomize, and follow patients. Group III institutions referred patients directly to the Massachusetts General Hospital for all procedures.



  • Warfarin (Coumadin┬«)Drug
    Other Names: Coumadin

Trial Design

  • Allocation: Randomized
  • Purpose: Prevention

Patient Involvement

Patients were randomized to receive warfarin alone with a target prothrombin ratio of 1.2 - 1.5 (estimated INR equivalent 1.5 - 2.7) or no warfarin (and aspirin if desired).


Type Measure Time Frame Safety Issue
Primary Ischemic stroke as determined by questionnaire every six months and contact with referring physicians every 3 and 9 months.
Secondary Systemic emboli, major and minor bleeding, and death.