Stratified Fascicular Conduction: A Cause of Predicted Interval Mismatch for Ablation of Premature Ventricular Contraction From the Left Posterior Fascicle.

BACKGROUND: The ablation target for premature ventricular contraction (PVC) can be predicted by comparing the His-ventricular (HV) or fascicular potential-to-ventricle (FP-V) interval during sinus rhythm (SR) and PVC, assuming equal bidirectional infrahisian conduction. CASE SUMMARY: The earliest retrograde fascicular potential with a fragmented electrogram (ERFP-FE) was recorded at the left posterior fascicle, where the FP-VPVC interval (34 milliseconds) matched the predicted HV interval [(HVSR + HVPVC)/2]. A sharp FP with a shortened FP-VSR interval (25 milliseconds) emerged after mechanical compression. Intra-FP conduction difference (duration of FPPVC-FPSR, Δ = 14 milliseconds) was inconsistent with FP-V interval disparity (interval of FPPVC-FPSR, Δ = 9 milliseconds), suggesting enhanced conduction from the FP terminal to ventricle during PVC (Δ = -5 milliseconds). Acute and 6-month success was achieved after ablation of ERFP-FE. DISCUSSION: Heterogeneous conduction of FP can cause a misleading FP-V interval, thereby confounding ablation targeting. TAKE-HOME-MESSAGE: In the presence of stratified FP conduction, ERFP-FE rather than the predicted FP-V interval may serve as a more reliable left posterior fascicle-PVC ablation target.