Mechanisms postulated for alternating bundle branch block are incomplete-and cycle-length-dependent-block in both the right and left bundle branches. A patient with severe longstanding cardiac conduction disease who developed alternating bundle branch block during treatment for advanced ischemic heart disease and malignant ventricular arrhythmia is presented. In this patient alternation was induced by atrial premature beats as well as spontaneous and pacemaker induced premature ventricular beats. Right bundle branch block which followed a premature atrial beat resulted from the longer refractory period of the right bundle. The maintenance of right bundle branch block at long cycle lengths was presumed to be due to continuous retrograde reentry. This was terminated when a pause following a premature beat allowed functional recovery of the right bundle branch. This patient died suddenly at home with a functioning pacemaker, demonstrating the high risk of death from ventricular dysrhythmia in the post myocardial infarction patient with a new conduction defect.
Bibliographical noteFunding Information:
From the Cardiovascular Division, Department of Medicine, Minneapolis Veterans Administration Medical Center and the University of Minnesota, Minneapolis, Minnesota. This project supported in part by a multidisciplinary cardiovascular research grant from the National Institutes of Health #5T32-HL07i84, and by Veterans Administration medical research funds. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefor be hereby marked "advertisement" in accordance with 18 U.S.C. w 1734 solely to indicate this fact. Reprint requests to: Arthur H. L. From, M.D. Cardiovascular Section, Veterans Administration Medical Center, 54th Street and 48th Avenue South, Minneapolis, MN 55417.