Intermittent tachycardia-dependent combined right bundle branch and left anterior conduction block.

A patient is described who had intermittent tachycardia-dependent combined right bundle branch and left anterior conduction block (left axis deviation) with simultaneous onset and disappearance during observations extending over 15 months. Although the site of conduction block could not be definitely determined the pathologic and electrophysiologic data suggest that there was a lesion in the distal part of the His bundle, presumably in fibers already arranged and predestined to supply the right bundle branch and left anterior areas. A single lesion at the so-called pseudobifurcation or two separate lesions with similar electrophysiologic consequences could also account for the observations.