What characterizes episodes of atrial fibrillation requiring cardioversion? Experience from patients with an implantable atrial cardioverter

Background Episodes of paroxysmal atrial fibrillation may cause disabling symptoms. Asymptomatic episodes of paroxysmal atrial fibrillation are, however, more common than symptomatic episodes. The aim of the study was to investigate whether episodes of atrial fibrillation for which the patient requires cardioversion differ from those in which the patient does not seek this therapy. Methods We studied 21 patients with atrial fibrillation treated with an implanted atrial cardioverter. The device displayed intracardiac electrograms from episodes of atrial fibrillation in which the patient received cardioversion and from episodes that did not lead to a hospital visit or cardioversion. The heart rate (mean, highest, and lowest) and the degree of ventricular interval irregularity were analyzed with these electrograms. Results There were 132 episodes of atrial fibrillation available for analysis, of which 73 led to cardioversion and 58 did not. Episodes leading to hospital/clinic visits and therapy had a higher maximum ventricular rate (130 vs 115/min, P = .0004) than episodes that did not cause the patients to seek therapy. This difference in heart rate was most prominent at the beginning of the episode, but tended to become more similar during the episode. There were no differences in ventricular cycle length irregularity between the 2 types of episodes. Moreover, treated episodes also had a significantly longer duration (mean duration 33 vs 9 hours, P = .002). Conclusions Episodes of atrial fibrillation that cause the patient to seek cardioversion are characterized by a high initial ventricular rate and a longer duration than those that go untreated. (Am Heart J 2003;145:670-5.)