Electrophysiological Characteristics of Fasciculoventricular Pathways

Fasciculoventricular (FV) accessory pathways are rare variants of pre-excitation, connecting the His-Purkinje system to ventricular myocardium. Though typically benign and not participating in tachycardia circuits, they can mimic septal accessory pathways on ECG, creating diagnostic challenges.

To assess the prevalence, ECG characteristics, electrophysiological features, and atypical properties of FV pathways in patients undergoing EP study at a tertiary center.

This retrospective observational study analyzed all patients undergoing EP study from 2010 to 2024. FV pathways were diagnosed by subtle pre-excitation, short and fixed HV interval, and lack of change in pre-excitation during atrial pacing.

Of 2836 patients undergoing EP study for supraventricular tachycardia, 668 had accessory pathways; 15 (2.2%) had FV pathways. The mean age was 26.5 years, with 53% male. Four patients (27%) were asymptomatic. Coexisting arrhythmias included AV accessory pathways (40%), AVNRT (20%), and atrial arrhythmias (15%). All patients showed subtle pre-excitation (mean PR 101 ± 18.7 ms, QRS 105 ± 14.4 ms). EP study revealed a short fixed HV interval (mean 17.6 ± 5.85 ms) with persistent pre-excitation during atrial pacing. Atypical features included intermittent FV conduction (13%), gap phenomenon (7%), and retrograde conduction (20%). FV pathways were not involved in any tachycardia circuit.

FV pathways are uncommon (2.2% of accessory pathways) with characteristic ECG and EP findings. The presence of gap phenomenon, intermittent antegrade conduction, and retrograde conduction suggests that a subset of these pathways may possess functional, discrete myocardial properties rather than passive insulation defects; however, further structural and electroanatomical studies are needed to confirm this hypothesis.