Abstract 12222: The Significance of Concealed Fasciculo-Ventricular Connections in His Bundle Pacing

Abstract

Introduction: It is almost 100 years ago since Mahaim described so-called paraspecific connections between the ventricular conduction axis and the crest of the muscular ventricular septum, believing such pathways to be ubiquitous. Hypothesis: These pathways have yet to be considered as potential pathways for septal activation during His bundle pacing Methods: So as to explore the hypothesis that specialized septal pathways provide the substrate for septal activation during His bundle pacing, we compared the findings from 22 serially sectioned histological datasets and 96 different individuals undergoing pacing of the His bundle. Results: We found extensive histologically specialized pathways connecting the branching bundle with the crest of the muscular ventricular septum in almost four-fifths of the histological datasets. A delta wave was observed in nine-tenths of the individuals undergoing His bundle pacing. Capture of the delta wave varied according to voltage, a finding which correlated with the distance of the septal pathways from the site of penetration of the ventricular conduction axis. Ventricular activation times remained normal in the presence of the delta wave. A significant decrease in ventricular activation times was observed in individuals with disease of the ventricular conduction system. Conclusions: Analysis of the effect of delta wave on ventricular activation times permits us to conclude that His bundle pacing captures the fasciculo-ventricular connections initially described by Mahaim as being paraspecific and ubiquitous.