Nonvalvular atrial fibrillation is the most common cardiac disorder causing stroke and systemic emboli. Atrial fibrillation affects approximately 4 percent of adults in the United States. Because its incidence increases with age, the risk of this disorder will increase as the U.S. population ages. An important aspect of treating atrial fibrillation is preventing systemic emboli and stroke. Nademanee and Kosar summarized the findings of five published studies that examined various treatments of atrial fibrillation, including the use of long-term antithrombotic medications alone, aspirin alone and combination therapy.

Patients with atrial fibrillation typically have thrombi in the left atrial appendage that are most likely caused by circulatory stasis. These thrombi can then embolize. Patients with structural heart disease or other risk factors are at much greater risk for emboli (see the accompanying table). Identification of the optimal treatment for patients with atrial fibrillation has generated much debate. Treatment with warfarin alone has been shown to decrease embolic vascular complications and stroke in patients with atrial fibrillation. In fact, the benefits of warfarin appear to increase when the International Normalized Ratio (INR) was 2 to 3 in patients with a history of stroke. Aspirin appears to be effective in treating nonvalvular atrial fibrillation in patients younger than 65 years who have no risk factors. However, warfarin remains the treatment of choice in most patients, particularly those who have had a previous transient ischemic attack or a minor stroke. Combination therapy using low-intensity, fixed-dose warfarin (target INR: 1.2 to 1.5) and aspirin (dosage: 325 mg per day) is less effective than adjusted-dose warfarin (target INR: 2 to 3), especially in patients with high-risk factors.

The authors conclude that the data from these five studies establish the following parameters: (1) the risk of stroke is very high in patients older than 75 years who have nonvalvular atrial fibrillation and in patients who have other high-risk factors; (2) warfarin is more effective than aspirin in preventing ischemic stroke and systemic emboli; (3) aspirin is effective in younger patients who do not have any other risk factors; and (4) the optimal intensity of warfarin has been established as an INR of 2 to 3.

The authors endorse the recommendations of the American College of Chest Physicians Consensus Conference on anti-thrombolytic therapy. First, patients younger than 65 years of age with no other risk factors should take aspirin. However, the presence of even one risk factor in patients in this group warrants the use of warfarin (INR: 2 to 3). Second, patients between 65 and 75 years with no risk factors may be treated with either aspirin or warfarin. If one or more risk factors are present, the patient should be treated with warfarin. Third, all patients over 75 years of age should be treated with warfarin (INR: 2 to 3).

An accompanying symposium between the author of this article and other physicians illustrates the many concerns surrounding the treatment of atrial fibrillation. The efficacy of aspirin in the treatment of any patient with atrial fibrillation is supported by only one study (Stroke Prevention in Atrial Fibrillation I and II), and many experts doubt the validity of the results. Another question concerns the duration of anticoagulation therapy with warfarin. Must it be continued for life even if the patient is accurately able to determine the presence or absence of fibrillation? What is the role of the newer antiplatelet medications? The only issue that appears to be clear is that patients with atrial fibrillation should be treated with antithrombotic medication to decrease the risk of systemic embolism and stroke.