Wide complex bigeminy: unusual presentation of an atriofascicular fiber.

Ventricular bigeminy in children is regarded as a benign arrhythmia in the absence of coexisting heart disease. We present the case of a patient with an atriofascicular fiber that electrocardiographically presented as wide complex bigeminy and wide complex tachycardia. At electrophysiologic study, the mechanism for the wide complex extrasystoles was reentry within the atriofascicular fiber or at its atrial insertion. Retrograde conduction within the fiber was also demonstrated under the influence of verapamil and ventricular extrastimulus testing. We conclude that conduction through an atriofascicular fiber should be included in the differential diagnosis of wide complex bigeminy having left bundle branch block morphology.