An Elderly Case of Supernormal Conduction in the Posterior Division of the Left Bundle Branch

An electrophysiologic study was performed in a 95-year-old man with bifascicular block (right bundle branch block and left anterior hemiblock). During sinus rhythm (AA interval=980ms), every sinus beat was conducted to the ventricle. The AH interval was 130ms and HV interval was 50ms. A programmed premature atrial stimulation was performed after 8 paced beats at a slightly shorter cycle length than the sinus cycle length (900ms). As the atrial coupling interval was shortened, the H1H2 interval also shortened. At an H1H2 interval of 680ms the premature atrial beat was blocked distal to the recording site of the His potential. The block persisted up to an H1H2 interval of 560ms. AV conduction resumed paradoxically when the H1H2 interval was further shortened to intervals lasting 540-490ms. During this period the H2V2 interval was 50ms. At still shorter H1H2 intervals, H2 was again blocked. The H2V2 intervals during this phase of improved conduction were unchanged compared with those of other conducted beats. Therefore normalization due to the gap phenomenon could be ruled out, and the improved conduction could be explained by a phenomenon of supernormal conduction in the posterior division of left bundle branch.