Ablation-Induced Change in the Course of Fascicular Tachycardia

Background: Multiform fascicular tachycardia (FT) was recently described as a ventricular tachycardia (VT) that has a reentrant mechanism using multiple fascicular branches and produces alternate fascicular VT forms. Ablating the respective fascicle may cause a change in the reentrant circuit resulting in a change in morphology, and ablation of the septal fascicle is crucial for successful ablation.

Objective: We describe four cases of FT in which ablation induced a change in QRS morphologies and aggravated clinical course.

Methods and Results: Four out of 57 consecutive FT cases in three institutions were retrospectively analyzed and found to involve multiform FT. They underwent electrophysiological study, fascicular potential mapping, and electro-anatomical mapping. All patients initially had FT with right bundle branch block (RBBB) and superior axis morphology. Radiofrequency catheter ablation (RFCA) targeting the distal left posterior fascicle (LPF) resulted in a second VT with an RBBB-inferior axis morphology that sometimes became faster and/or incessant and/or verapamil-refractory in characteristics. RFCA in the upper septum abolished the second VT with no complications and uneventful long-term follow-up.

Conclusion: The change in FT morphology during ablation may be associated with a change in clinical course when shifting from one route to another and may aggravate symptoms. Targeting of the proximal conduction system (such as bifurcation, LPF, left anterior fascicle, high septal/auxiliary pathway) may serve to solve this problem.