Subtherapeutic anticoagulation: the bane of conventional anticoagulation for cardioversion of atrial fibrillation.

Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice, affecting slightly less than 1% of the general population. Patients with AF suffer from a decrease in functional capacity secondary to a combination of palpitations, dyspnea, myocardial ischemia, congestive heart failure and hypotension. In addition, unorganized atrial electrical and mechanical activity result in blood stasis and the formation of atrial thrombi placing the patient at risk of systemic thromboembolism. It is therefore important, if feasible, to attempt cardioversion (CV) to normal sinus rhythm (NSR) in these patients. The most concerning complication of CV in AF is systemic thromboembolism, and more specifically stroke. In 1960, Goldman reported a 1.5% embolization event rate in 400 AF patients undergoing chemical CV who had not received anticoagulation. This study proposed for the first time that anticoagulant therapy initiated prior to CV could stabilize pre-existing thrombus allowing it to organize and adhere to the atrial wall. The first report of thromboembolism associated with electrical CV occurred in 1963 when Lown et al. examined 50 AF patients. In this series, 94% of patients had rheumatic heart disease and systemic embolization was reported in 1.7%. Anticoagulation therapy was restricted only to patients with mitral stenosis. A few years later, Lown reported the results of a series of 350 patients undergoing electrical CV for AF. This study documented a 0.9% incidence of systemic embolization. Interestingly, only 29% of patients received anticoagulant agents and all