CARDIOVERSION OF NONRHEUMATIC ATRIAL-FIBRILLATION - REDUCED THROMBOEMBOLIC COMPLICATIONS WITH 4 WEEKS OF PRECARDIOVERSION ANTICOAGULATION ARE RELATED TO ATRIAL THROMBUS RESOLUTION

Background The use of warfarin anticoagulation for several weeks befor e cardioversion results in a 90% reduction in the incidence of cardiov ersion-related thromboembolism. The mechanism of this benefit, however , is unknown; it has been widely attributed to organization and adhere nce of atrial thrombi, a finding observed among pathological studies o f patients with rheumatic valvular disease. Methods and Results Serial transesophageal echocardiography was performed in 14 patients with no nrheumatic atrial fibrillation after identification of atrial thrombi on initial transesophageal study. All patients received warfarin antic oagulation and were followed clinically for signs of thromboembolism. Eighteen atrial thrombi were identified on initial transesophageal stu dy, including 14 thrombi confined to the left atrial appendage, 2 in t he body of the left atrium, 1 in the right atrial appendage, and 1 in the body of the right atrium. Thrombus size varied from 5 to 20 mm, an d 6 were considered mobile. After a median of 4 weeks of warfarin, 16 of 18 atrial thrombi (89%; 95% CI, 73% to 100%) had completely resolve d on transesophageal echocardiographic study. In addition, no new thro mbi were identified on follow-up study, and no patient had a clinical thromboembolic event between studies. Conclusions These data strongly support the hypothesis that among patients with nonrheumatic atrial fi brillation, the mechanism of clinical benefit with 3 to 4 weeks of war farin before cardioversion is related to thrombus resolution and preve ntion of new thrombus formation rather than thrombus organization.