Electrophysiological Characteristics of Fasciculoventricular Pathways

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