Current guidelines recommend four weeks of anticoagulation after electrical cardioversion of atrial fibrillation or flutter to reduce the risk of thromboembolic events. Berger and Schweitzer pooled the data from 32 studies (4,621 patients) to assess the timing of embolic complications following cardioversion and to examine whether four weeks of anticoagulation are warranted after electrical cardioversion to sinus rhythm.

Studies were included if they contained at least 10 patients who underwent electrical cardioversion of atrial fibrillation or flutter and if the interval between electrical cardioversion and the occurrence of embolic events was clearly stated. An embolic event occurred after cardioversion in 92 (2 percent) of the 4,621 patients. The underlying cardiovascular or systemic disorder that predisposed to atrial fibrillation or flutter included rheumatic heart disease (17 patients), hypertension (12 patients), coronary artery disease (12 patients), dilated cardiomyopathy (five patients), hypertrophic cardiomyopathy (five patients), chronic obstructive pulmonary disease (three patients), congestive heart failure (two patients), alcohol abuse (two patients), aortic stenosis (one patient), mitral valve prolapse (2 patients) and thyrotoxicosis (one patient). Seventeen patients had no underlying heart disease and were classified as having lone atrial fibrillation. The embolic event occurred in three patients who had atrial fibrillation for no longer than two days before cardioversion.

The interval between cardioversion and the thromboembolic event ranged from less than one day to 18 days. Of the 92 events, 75 (82 percent) occurred within three days of cardioversion, 88 (96 percent) within one week and 90 (98 percent) within 10 days of cardioversion. In the two remaining patients, embolic episodes occurred on the 15th day and the 18th day after cardioversion.

The authors conclude that since embolic episodes rarely occurred more than 10 days after electrical cardioversion, two weeks of anticoagulant therapy might be sufficient in patients undergoing electrical cardioversion of atrial fibrillation or flutter. They also suggest that even shorter periods of anticoagulation might be a consideration in patients at high risk of bleeding complications.