His–Purkinje system longitudinal dissociation: From bench to bedside. A case of output‐dependent fascicular capture

Abstract

Introduction: Histological studies reported that the His bundle (HB) is partitioned into narrow cords by collagen running in its long axis, providing the anatomical setting necessary for its longitudinal dissociation. Further confirmations came from the demonstration that direct HB pacing normalizes the QRS axis and duration in subjects with proximal HB lesions causing bundle branch block. However, there is no evidence of the possibility of selective HB partitions pacing destined to the composition of branches and fascicles. Methods and Results: We describe a case of intra‐Hisian left bundle branch block in which permanent distal HB pacing corrects left ventricular delay and produces different QRS morphology at different voltage outputs, as an expression of different selective HB compartments recruitment. Conclusion: This case would strengthen the limited data in the literature about HB longitudinal dissociation.

Electro-energetics of Biventricular, Septal and Conduction System Pacing

“…However, higher voltages are needed in less optimal positions (non-selective HBP). [ 48 ] Bednarek et al investigated mechanical dyssynchrony using speckle tracking echocardiography in patients during selective and non-selective HBP. [ 49 ] Speckle tracking images showed premature contraction in the basal septal segment only during non-selective HBP, but this was confined to the basal septum and basal inferior segment.…”

Interesting phenomena during threshold testing of conduction system pacing: What is the mechanism?

“…We believe this phenomenon has been referred to as output‐dependent fascicular capture. Different outputs can selectively activate different portions of conduction system and produced asynchronous conduction in the HPS 9,10 . At the initial threshold testing, pacing output at 2 V/0.5 ms activated the HPS and the myocardium.…”

Lack of evidence for longitudinal dissociation of the atrioventricular conduction axis

“…Electrophysiological studies performed in dogs, however, conclusively demonstrated the presence of functional transverse interconnections within the non‐branching bundle, failing to demonstrate the delivery of the stimulus to specific ventricular areas (Lazzara et al, 1973). The topic, however, is far from settled, as evidence of dissociation has allegedly been found in pathological situations (Marinaccio et al, 2021; Sherif et al, 1974; Zhang, 2014) In this regard, a letter commenting on the publication of James and Sherf (Lev, 1971), emphasized the difficulty in establishing the presence of morphological dissociation when only using evidence depending on two‐dimensional anatomy, this being the methodology of the studies performed at that time. It was argued that three‐dimensional reconstructions would provide the best means of proving or disproving the presence of lateral or transverse interconnections.…”