Ventricular Tachycardia Substrates in Children and Young Adults With Repaired Tetralogy of Fallot

BACKGROUND: Patients with repaired tetralogy of Fallot (rTOF) have a time-dependent increased risk of ventricular tachycardia (VT). Slow conducting anatomical isthmuses (SCAIs) are the dominant VT substrates in adults with rTOF. It is unknown if they are present at younger age. OBJECTIVES: This study aimed to characterize VT substrates in patients with rTOF <30 years of age. METHODS: Data of consecutive patients with rTOF aged <30 years who underwent electroanatomical mapping and programmed electrical stimulation between 2005 and 2022 were analyzed. RESULTS: Fifty-five patients were included (median age: 15.8 years, IQR: 13.8-21.8 years; 15 repaired via ventriculotomy; 13 complex TOF variants). Twelve patients had right ventricle-to-pulmonary artery conduits inserted during initial repair or had early pulmonary valve replacement (PVR) (<1 year after repair). Indications for electroanatomical mapping and programmed electrical stimulation were spontaneous VT, before PVR, and risk stratification in 5, 40, and 10 patients, respectively. In 16 patients (29%), SCAI 3 was identified; no other SCAI was present. Monomorphic VT was inducible in 8 and related to SCAI 3 in 7 patients. Identified VT substrates were targeted by ablation. Right ventricle-to-pulmonary artery conduit/early PVR, ventriculotomy, and complex TOF were associated with SCAI 3 in univariable analysis. During a median follow-up of 5.3 years, VT recurred in 2 patients. No patients died. CONCLUSIONS: In young patients with rTOF, SCAI 3 is the dominant substrate for VT. Complex TOF and interrelated type and timing of (re-)operation may contribute to the development of SCAI 3 already at a young age.