Electrical conversion of atrial flutter to atrial fibrillation. Flutter mechanism in man.

If human atrial flutter is due to re-entrant excitation, depolarization as well as repolarization must continue throughout the entire atrial cycle. It follows that the atrial vulnerable period for inducing atrial fibrillation is also continuous rather than discrete. This hypothesis was examined during cardioversion of I33 patients with atrial flutter who received 280 low-energy shocks. A composite analysis of these patients demonstrated that all intervals of the flutter cycle were equally susceptible to shock-induced atrial fibrillation. The optimal energy was found to be io Wsec. The development of atrialfibrillation was independent of the state of digitalization and was not prevented by pretreatment with atropine or propranolol. These findings are consistent with re-entry as the basic mechanism of human atrial flutter.