Clinical and Electrophysiological Characteristics of Inducible Polymorphic Ventricular Tachycardia in Repaired Tetralogy of Fallot.

Background: Although sustained monomorphic ventricular tachycardia (MVT) in repaired tetralogy of Fallot (TOF) is linked to abnormally conducting anatomical isthmuses, the clinical importance of inducible polymorphic ventricular tachycardia (PVT) is unclear.

Objectives: The aim of this study was to determine the clinical and electrophysiological characteristics of inducible PVT in TOF.

Methods: Patients from the ongoing CATAPULT-TOF (Catheter Ablation of Ventricular Tachycardia Before Transcatheter Pulmonary Valve Replacement in Repaired Tetralogy of Fallot) registry with inducible sustained PVT at index electrophysiology study were included. Abnormal anatomical isthmus was defined as conduction velocity <0.5 m/s. Centrally adjudicated episodes with ≥3 consecutive beats of similar morphology (10 of 12 leads) were labeled transiently organized PVT (TO-PVT). TO-PVT was analyzed in relation to three-dimensional substrate characteristics and postablation inducibility.

Results: Of 186 patients (mean age 40 years; 55% male), sustained PVT was induced at 27 procedures (15%). Patients with PVT vs MVT were more likely to undergo operation in the current era (P = 0.008), not require palliative shunt (P = 0.01), exhibit a lower right ventricular end-diastolic volume/left ventricular end-diastolic volume ratio (P = 0.02), and harbor faster anatomical isthmus conduction velocity (P = 0.03). Of those with available electrocardiography data, greater number of TO beats was associated with ≥1 anatomical isthmus (median 3 vs 0 beats; P = 0.001). The proportion with TO-PVT decreased with catheter ablation, with 14 of 24 identified at baseline (58%; median 3.5 beats; cycle length 181 milliseconds), 3 (23%) of 13 postablation, and 1 (8%) of 13 at follow-up electrophysiology study (P_trend = 0.001).

Conclusions: Patients with inducible PVT display a lower clinical risk profile and healthier myocardial substrate than those with MVT. Organized beats at episode onset appear to be associated with anatomical isthmuses that can be targeted by catheter ablation.