Studies of non-primary care patients with atrial fibrillation have shown that coumadin therapy reduces the risk of thromboembolic events by 68 percent, compared with 36 percent for aspirin therapy. Conversely, evidence from primary care practices suggests that aspirin therapy may be an effective preventive measure and may also be associated with a lower risk of hemorrhagic complications than coumadin therapy. Hellemons and colleagues conducted a study comparing aspirin with standard- and low-intensity anticoagulation using coumadin in the treatment of elderly patients with atrial fibrillation.

More than 700 patients were recruited from 284 general practices for inclusion in the study. All patients were at least 60 years of age and had untreatable atrial fibrillation confirmed by electrocardiography. Exclusion criteria included contraindications to aspirin or coumadin, previous stroke, recent history of myocardial infarction, cardiomyopathy, gastrointestinal bleeding or severe renal or hepatic disease. Patients were stratified by their eligibility for standard anticoagulation and then randomly assigned to one of three treatment groups. Standard-intensity anticoagulation therapy aimed to maintain an International Normalized Ratio (INR) of 2.5 to 3.5. Patients who were randomized to receive low-intensity coumadin therapy tried to maintain an INR of 1.1 to 1.6. These patients were monitored every two to six weeks. The remaining patients received 150 mg of aspirin per day, and pill counts were used to monitor compliance. The mean follow-up period was 2.7 years. The primary outcomes measured were stroke, arterial embolism, major hemorrhage and vascular death. Patients were also monitored for myocardial infarction, retinal infarction, transient ischemic attacks, minor bleeding complications and all other causes of death.

No patients were lost to follow-up, but 77 patients withdrew for medical reasons and 92 for other reasons during the study. Compliance with the assigned medications was notably high. During follow-up, 157 major or fatal events were documented. The Kaplan-Meier survival analysis for primary outcome events, according to treatment group, is shown in the accompanying figure. The annual rate of major events was 5.5 percent. Compared with aspirin therapy, the hazard ratio of major events was 0.91 for low-intensity anticoagulation and 0.78 for standard-intensity anticoagulation. No significant differences in the incidence of bleeding complications were detected among the treatment groups. The overall annual rate of major bleeding events was 1.2 percent and of minor bleeding events was 2.7 percent. The rate of stroke was 1 percent in patients less than 78 years of age and 4 percent in older patients. Older age and hypertension were predictors of stroke.

The authors stress that elderly patients with stable atrial fibrillation who are closely monitored in general practice settings have a low rate of serious complications. In this large study, aspirin was as effective as standard- or low-intensity coumadin therapy in preventing complications of atrial fibrillation. Because monitoring and maintaining compliance with aspirin therapy is easier for patients and physicians, the authors recommend that aspirin be the treatment of choice in low-risk primary care patients with atrial fibrillation.