Approach to the Diagnosis and Management of Complex Fascicular Ventricular Tachycardias

Complex ventricular tachycardias involving the fascicular system (fascicular ventricular tachycardias [FVTs]) can be challenging. In this review, we describe our approach to the diagnosis and ablation of these arrhythmias with 10 illustrative cases that involve (1) differentiation from supraventricular tachycardia; (2) assessment for atypical bundle branch reentry and other interfascicular FVTs; (3) examination of P1/P2 activation sequences in sinus rhythm, pacing, and tachycardia; and (4) entrainment techniques to establish the tachycardia mechanism and aid circuit localization. To summarize, 5 cases had prior ablation with 2 previously misdiagnosed as supraventricular tachycardia. A short His-ventricular interval supported ventricular tachycardia. Atrial stimulation could initiate and entrain 4 FVTs. P1 potentials were recorded in all cases of left posterior FVT. Entrainment at P1 and P1 to P2 connection sites at the mid-septal region, and the postablation emergence of a late P1 with decremental properties, is consistent with the left septal fascicle being the slowly conducting, retrograde limb of the left posterior FVT circuit. Ablation targeting the mid-septal left septal fascicle and P1 to P2 connection sites successfully eliminated left posterior FVT. Right ventricular apical pacing was useful in differentiating bundle branch reentry and focal FVTs from reentrant FVTs. Two cases exhibited bundle branch reentry and other interfascicular FVTs. Three cases were postinfarct FVTs involving the LPF, where pacing and entrainment at sites of conduction system potentials were able to localize sites critical for ablation, in contrast to previously unsuccessful substrate modification. In conclusion, several ventricular tachycardia mechanisms involving the fascicular system can occur in both structurally normal and abnormal hearts. A high index of suspicion is required given their rarity and potential for misdiagnosis. Once identified, we emphasize a structured approach to the diagnosis and management of FVTs to confirm the mechanism and localize suitable ablation targets involving careful recording of conduction system potentials and pacing/entrainment maneuvers.