Bleeding during warfarin and aspirin therapy in patients with atrial fibrillation: the AFASAK 2 study. Atrial Fibrillation Aspirin and Anticoagulation.

BACKGROUND

Treatment with warfarin sodium is effective for stroke prevention in atrial fibrillation but many physicians hesitate to prescribe it to elderly patients presumably because of the associated risk for bleeding and the inconvenience of frequent blood tests for the patients.

METHODS

In the Second Copenhagen Atrial Fibrillation, Aspirin, and Anticoagulation (AFASAK 2) Study, we studied the rate of bleeding events associated with the incidence of thromboembolic events in patients receiving warfarin sodium, 1.25 mg/d; warfarin sodium, 1.25 mg/d, plus aspirin, 300 mg/d; aspirin, 300 mg/d; or adjusted-dose warfarin therapy aiming at an international normalized ratio of the prothrombin time ratio (INR) of 2.0 to 3.0. The study was scheduled for 6 years from May 1, 1993, but owing to evidence of inefficiency of low-intensity therapy plus aspirin from another study it was prematurely terminated on October 2, 1996. Minor and major bleeding events were recorded prospectively. The rate of bleeding was calculated using the Kaplan-Meier method and risk factors were identified by the Cox proportional hazards model.

RESULTS

Of 677 included patients, 130 (median age, 77 years; range, 67-89 years) experienced bleeding. One woman and 12 men experienced major bleeding. Four had intracranial bleeding: 2 cases were fatal and 2 were nonfatal. During treatment with mini-dose warfarin, warfarin plus aspirin, aspirin, and adjusted-dose warfarin, the annual rate of major bleeding was 0.8%, 0.3%, 1.4%, and 1.1%, respectively (P = .20). After 3 years of treatment the cumulative rate of any bleeding was 24.7%, 24.4%, 30.0%, and 41.1% (P = .003), respectively. Increasing INRvalue (P<.001) and prior myocardial infarction (P = .001) were independent risk factors for bleeding, whereas increasing age was not.

CONCLUSIONS

Fixed mini-dose warfarin and aspirin alone or in combination were associated with both minor and major bleeding. The small number of major bleeding events in patients receiving adjusted-dose warfarin therapy as compared with those receiving less intensive antithrombotic treatments and the finding of no significant influence of age on the risk for bleeding indicate that even elderly patients with atrial fibrillation tolerate adjusted-dose warfarin therapy (INR, 2.0-3.0).