Abstract 15222: Slowly Conducting Anatomic Isthmuses of Repaired Tetralogy of Fallot: A Role for “Prophylactic VT Ablation”

Background: Ventricular tachycardia (VT) is common in patients with repaired tetralogy of Fallot (rToF) and involves 5 slowly conducting isthmuses (SCAI) bound by the right ventriculotomy, ventricular septal defect (VSD) patch, tricuspid valve, and pulmonic valve.

Aims: We aim to study the safety and efficacy of a strategy in which rToF patients undergo prophylactic radiofrequency ablation of any SCAI to prevent incident VT.

Methods: Patients underwent voltage and activation mapping in sinus rhythm. Abnormal isthmuses were identified by low voltage (≤ 1.5 mV) without pre-existing conduction block. Isthmuses with conduction velocity (CV) ≤ 0.5 m/s (SCAI) were then ablated. Post-ablation, ventricular programmed stimulation was performed with triple extrastimuli from two sites. Outcomes of prophylactic ablation patients were compared to rToF patients undergoing clinical VT ablation within the same period.

Results: Indication for prophylactic SCAI ablation included pre-pulmonic valve replacement (77%), atrial arrhythmia ablation (11%), syncope (5%), and NSVT (5%). Of 44 prophylactic patients, 32 (73%) had at least one isthmus and 25 (57%) had at least one SCAI (mean 0.7 ± 0.7 SCAI/patient), with the most common being SCAI 3 (36%) and 4 (32%) (see figure). After prophylactic ablation, bidirectional block was achieved across all SCAI and no VT was inducible post-ablation. Over a median 10.5 [IQR 3, 20] month follow-up, there was no sustained VT, sudden cardiac death, or appropriate shocks. Among 18 patients undergoing clinical VT ablation, 16 (89%) had at least one SCAI (mean 1.5 ± 0.8 SCAI/patient, p=0.0002 compared with prophylactic group), most commonly SCAI 3 (83%). One (6%) VT patient had recurrent VT during follow-up of 15.5 [IQR 6, 33] months. There were no peri-procedural complications in either group.

Conclusions: Prophylactic SCAI ablation for patients with rToF is safe, acutely successful, and associated with excellent short-term outcomes.