Mobitz type I atrioventricular block in the ventricular specialized conduction system.

A patient with a history of multiple syncopal episodes had electrocardiographic findings of Wenckebach type of second degree atrioventricular block and left bundle branch block. He was thought to have intermittent complete heart block. His bundle recordings demonstrated the unusual occurrence of Mobitz type I block localized to the ventricular specialized conduction system. Based on the findings of this case and those of previous case reports, it is recommended that electrophysiologic studies should be performed on all patients with Mobitz type I atrioventricular block who also have bundle branch block.