While the management of atrial fibrillation includes anticoagulation, the value of this treatment for atrial flutter is less well established. Seidl and associates conducted a retrospective study to assess the frequency of thromboembolism in patients hospitalized with atrial flutter as the primary rhythm disorder.

A total of 191 patients with chronic or recurrent atrial flutter, defined as organized atrial tachycardia at a rate of 240 or more beats per minute on a 12-lead electrocardiogram, were included in the study. Electrical cardioversion was performed in 138 patients (72.3 percent), catheter ablation was used in 28 patients (14.7 percent), medical cardioversion was used in 19 patients (9.9 percent) and overdrive stimulation was used in six patients (3.1 percent). Warfarin therapy had been administered in 67 of the patients several weeks before and after cardioversion. An additional 72 patients were receiving aspirin.

Acute embolic events within 48 hours of cardioversion were distinguished from later embolic events during long-term follow-up and before hospital admission. The overall embolic event rate, including a history of thromboembolism, acute embolism and a thromboembolic event during follow-up, was 11.5 percent (22 of the 191 patients). A remote history of a systemic embolic event was found in 5.8 percent (11 of 191 patients). Following direct-current cardioversion, three of 138 patients (2.2 percent) sustained a cerebrovascular incident within 48 hours. During long-term follow-up (about 26 months) nine patients (4.7 percent) had an embolic event.

Three of 67 patients who received effective anticoagulation (4.5 percent) had an embolic event during follow-up. In contrast, 10 of the 124 patients who did not receive anticoagulation (8.1 percent) or who received an ineffective amount incurred an embolic event. Risk indicators for an embolic event included organic heart disease, depressed left ventricular function, hypertension and diabetes mellitus. A history of hypertension was the only independent risk factor.

The authors conclude that the annual risk of an embolic event in patients with atrial flutter is approximately 1.8 percent, approximately one third of the 4.5 percent annual risk in patients with nonrheumatic atrial fibrillation. Anticoagulation therapy may decrease this risk.

In an accompanying editorial, Dunn agrees that atrial flutter poses an increased risk of an embolic event and that anticoagulation is appropriate in patients with this condition. Further study may be useful to determine if different forms of atrial flutter, as determined by the direction of depolarization, may be associated with different risks of thromboembolism.