Intermittent fasciculoventricular pathway: ECG and electrophysiologic findings, clinical implications

Evidence for concealed fasciculo-ventricular connections as revealed by His bundle pacing

BACKGROUND

It is almost 100 years ago since Mahaim described the so-called paraspecific connections between the ventricular conduction axis and the crest of the muscular ventricular septum, believing such pathways to be ubiquitous. These pathways, however, have yet to be considered as potential pathways for septal activation during His bundle pacing.

MATERIALS

So as to explore the hypothesis that specialised septal pathways might provide the substrate for septal activation during His bundle pacing, we compared the findings from 22 serially sectioned histological datasets and 34 different individuals undergoing His bundle pacing.

RESULTS

We found histologically specialised pathways connecting the branching component of the atrioventricular conduction axis with the crest of the muscular ventricular septum in almost four-fifths of the histological datasets. In 32 of 34 patients undergoing His bundle pacing, the QRS complex closely resembled published images of known conduction through fasciculo-ventricular pathways. In only two patients was a delta wave not seen at any pacing voltages. Capture of these connections varied according to pacing voltage, a finding which correlated with the distance of the pathways from the site of penetration of the ventricular conduction axis. Ventricular activation times remained normal in the presence of the delta wave at higher pacing voltage but were prolonged at lower voltages.

CONCLUSIONS

Our histologic findings confirm fasciculo-ventricular connections, initially described by Mahaim as being paraspecific, are likely ubiquitous. Analysis of 12-lead electrocardiograms leads us to conclude that fasciculo-ventricular pathways, concealed during sinus rhythm, become manifest with His bundle pacing.

Is radiofrequency ablation of accessory pathways always necessary? The case of a variant of Wolff-Parkinson-White syndrome

A 16-year-old boy was referred for radiofrequency ablation of an accessory pathway. He had not experienced palpitations, but a normal electrocardiogram was a prerequisite for enrollment in a professional soccer school. The electrocardiogram showed a PR interval of 0.10 second and wide QRS complexes suggestive of an accessory pathway. The case of a variant of Wolff-Parkinson-White syndrome is discussed.