Bundle-branch block with periods of normal intraventricular conduction: Report of an unusual case

The electrocardiographic tracings taken from a sixty-six-year-old man who had no cardiac symptoms showed a typical bundle-branch block which abruptly disappeared with the spontaneous occurrence of 2:1 A-V block, and which disappeared after cardiac slowing, the result of indirect vagal stimulation. This is the fourth instance of proved type 2 bundle-branch block to be reported. It is believed that the conduction disturbance in this instance was primarily the result of fatigue of the bundle and that the depressed tissue was small in extent.