[Resynchronization of left bundle branch block by His bundle pacing : A case series].

The possibility to correct left bundle branch block by His bundle pacing seems to contradict our understanding of the conduction system. However, we present a series of 6 consecutive patients in which distal, nonselective His bundle pacing led to partial or complete correction of left bundle branch block which suggests a damage of fibers of the left bundle within the His bundle proximal to the pacing site. Also left bundle branch block morphologies with electrocardiogram (ECG) criteria predictive of diffuse or distal conduction block were successfully corrected by His bundle pacing. Therefore, we postulate that His bundle pacing can have a positive impact even on left bundle branch block with multiple, diffuse, and distal conduction disturbances. Mechanisms for this are not clear but may relate to "recruitment" of diffusely disturbed conduction fibers, capture of distal fibers of the left bundle as well as areas of septal myocardium by pacing and concealed conduction. These observations question our understanding of left bundle branch block and suggest that the block is frequently located proximal to the division in right and left Tawara branches and can be corrected by His bundle pacing.