Slowly Conducting Anatomic Isthmuses of Tetralogy of Fallot: An Opportunity for "Prophylactic" VT Ablation.

Background: Patients with repaired Tetralogy of Fallot (rTOF) are at risk of ventricular tachycardia (VT) and sudden cardiac death (SCD). Most VTs arise from 5 slowly conducting isthmuses (SCAI; conduction velocity ≤ 0.5 m/s) bound by the right ventriculotomy, ventricular septal defect patch, tricuspid and pulmonic valves. Historically, risk stratification electrophysiology studies (EPS) involved programmed ventricular stimulation (PVS) with VT induction guiding ICD implantation and/or VT ablation.

Objective: To evaluate a "prophylactic" strategy of ablating SCAI even in the absence of inducible VT to reduce ICD implantation and arrhythmic events, and to compare this to the "historical" strategy.

Methods: This was a single-center, retrospective cohort study. The "historical cohort" underwent PVS to guide ICD implantation and/or VT ablation. The "prophylactic cohort" underwent right ventricular electroanatomic mapping and ablation of SCAI. A composite endpoint of arrhythmic death, cardiac arrest, sustained VT, and ICD complication was compared between the cohorts.

Results: Ninety-three patients with rTOF had risk stratification EPS. Of 57 prophylactic patients, SCAI were identified/ablated in 33 (58%), 16 (28%) had inducible VT before ablation, and 1 received ICD. Of 35 historical patients, 15 (43%) had inducible VT: 3 had cryoablation during PVR and 11 received ICD. No prophylactic patients met the composite endpoint over median 21 months (IQR 8,35) versus 10 (29%) historical patients over median 125 months (IQR 90,142; p= 0.017). There were no ablation-related complications.

Conclusion: Prophylactic SCAI ablation is associated with fewer ICD implants and a reduction in incident arrhythmic events without ablation-related complications.