Left bundle branch pacing shortened the QRS duration of a right bundle branch block.

Left bundle branch pacing (LBBP) has recently emerged as a novel physiological pacing technique with a paced morphology of a pseudoright bundle branch block (RBBB). We herein present a 63-year-old man with a high-degree atrioventricular block and complete RBBB, whose intrinsic QRS duration and terminal R' wave duration in V1 were significantly shortened after LBBP and further shortened with the increase in output.