Conflicting invasive electrophysiological study results in a suspected fasciculoventricular pathway: a case report.

Background: Fasciculoventricular pathways (FVPs) are variants of pre-excitation syndrome with uncertain prevalence in the human heart. This case report presents findings from an invasive electrophysiological study (EPS) that mostly fulfil the established diagnostic criteria for FVP, but also exhibit atypical features, highlighting diagnostic ambiguity in clinical practice. Case summary: A 23-year-old patient presented with a history of brief, weekly episodes of palpitations. The resting surface ECG demonstrated a pre-excitation pattern suggestive of either a parahisian or fasciculoventricular pathway. The EPS findings were largely consistent with a FVP. During junctional beats, we observed a loss of pre-excitation and normalization of HV-interval. No tachycardia was inducible, and there was no evidence of retrograde conduction via an accessory pathway. Discussion: Three potential anatomical locations of the upper FVP take-off side were considered: (i) a single FVP originating from the lower part of the His-bundle or (ii) a single FVP originating close to the upper, junctional part of the His-bundle or even from the distal part of the AV-node and (iii) the presence of an additional second accessory pathway. Based on the above-mentioned evidence, the second anatomical location of the upper FVP-insertion was most likely, differing from previous findings of FVP in the literature. A conservative, observational management strategy was adopted. Current diagnostic criteria for FVP are based on retrospective studies and case reports, lacking prospective validation. This case underscores the need for further research to refine the diagnostic approach to FVP and improve risk stratification in such patients.