Anticoagulation and atrial fibrillation

Abstract

The decision to anticoagulate patients with atrial fibrillation (AF) involves weighting the risk of an embolic event without therapy versus the risk of a hemorrhagic event on therapy. Improved methods of monitoring anticoagulation with the International Normalized Ratio (INR), and recent evidence of the efficacy and safety of low-dose warfarin (INR range 2.0 to 3.0) have clarified the role of anticoagulation in AF. Over the past four years, five large prospective randomized trials in patients with nonvalvular atrial fibrillation (NVAF) have reported substantial reductions in stroke in patients treated with low-dose warfarin therapy. The results of these trials, combined with previous studies, suggest that anticoagulation is the treatment of choice for patients with atrial fibrillation associated with rheumatic valvular disease, prosthetic valve disease, and now NVAF. Although the results of the prospective atrial fibrillation trials are very consistent in regard to the efficacy and safety of anticoagulation, there continues to be uncertainty regarding which subgroups of patients are at highest risk for embolic events. Subgroups that appear to be at high risk include patients with hypertension, previous embolic events, structural heart disease (enlarged left atrial size, previous myocardial infarction, left ventricular dysfunction), and older age. Young patients with no evidence of structural heart disease or hypertension (lone atrial fibrillation) have a low embolic rate and do not warrant anticoagulation. Recent studies suggest that there is little difference in the risk of stroke in patients with paroxysmal or chronic AF, therefore this factor should not have a major impact on therapeutic decisions. Anticoagulation is also recommended for patients undergoing elective cardioversion (recent onset of atrial fibrillation greater than two days in duration), and patients with atrial fibrillation and hyperthyroidism because of studies suggesting a higher rate of embolism if these patients are not anticoagulated. The role of aspirin in AF is less clear as only two of the five prospective trials randomized patients to aspirin therapy and only one documented aspirin benefit. Therefore, aspirin appears to offer less benefit but is a satisfactory alternative to warfarin therapy. Aspirin is currently recommend for patients who are poor candidates for anticoagulation or individuals with AF who are considered to be at low risk for stroke.