Ventricular monophasic action potentials during intermittent left bundle branch block

A case of intermittent left bundle branch block is presented. Simultaneous recording of right and left ventricular monophasic action potentials allowed a more accurate demonstration of delayed left ventricular activation during intermittent left bundle branch block. His bundle electrogram was also of great help in the interpretation of infrahisian conduction in the patient studied. These methods may be useful in the complex electrophysiologic investigation of certain cases.