When the body and appendage of the left atrium disagree: "Focal" atrial fibrillation-implications for atrial thrombus formation and risk of thromboembolism.

A case is presented of a man who had 5 hours of atrial fibrillation followed by spontaneous conversion and maintained sinus rhythm that persisted as shown by surface electrocardiography. Transesophageal echocardiography performed 24 hours after electrocardiographic conversion documented an atrial fibrillation pattern within the left atrial appendage, with a normal sinus Doppler pattern in the body of the left atrium. This apparent regional discrepancy in atrial function may partially explain the increased risk for "late" thromboembolism among patients with atrial fibrillation who appear to be successfully converted with sustained sinus rhythm.