Catheter ablation is a first-line treatment for fascicular ventricular tachycardia (VT). However, insufficient ablation may cause exit site change, which mimic another VT. We illustrated a case of insufficient VT ablation with different exit site. A 49-year-old woman was admitted for electrophysiology study due to palpitation. During the electrophysiology study, the first VT morphology revealed an RBBB pattern favouring a posterior fascicular (LPF) VT. During the LPF ablation, the first VT converted to a second VT, which revealed anterior fascicular-like VT. The activation map of the fascicular potentials and ventricular potentials revealed that the earliest fascicular activation was at the posterior fascicle near the first ablation site, with propagation to the anterior fascicle (LAF), whereas the earliest ventricular activation propagated from the anterior fascicle region to the rest of the ventricle including the substrate near the posterior fascicle. The block distal to the localized-reentry circuit of the first ablation might be created, and the fascicular potential propagated to LAF from LPF to exit. Catheter ablation at the earliest ventricular activation site near the LAF (exit to the ventricle) could not terminate the VT; however, ablation proximal to the earliest ablation site (of the LPF) terminated the tachycardia and the VT became non-inducible thereafter.
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