Ventricular tachycardia substrates in young patients with repaired tetralogy of fallot
Authors: Wallet J , Kimura Y , Blom N A , Jongbloed M R M , Bertels R A , Hazekamp M , Zeppenfeld K 
Published: May 2023

Abstract

Funding Acknowledgements
Type of funding sources: Foundation. Main funding source(s): We acknowledge the support from the Netherlands Cardiovascular Research lnitiative: An initiative with support of the Dutch Heart Foundation and Hartekind.

Background
Patients with repaired tetralogy of Fallot (rTOF) have a time-dependent increase in risk of ventricular tachycardia (VT) after the age of 30 years (Y), with slow conducting anatomical isthmus (SCAI) 3, located between the pulmonary annulus and the ventricular septal defect (VSD) patch, as dominant VT substrate (1-4). However, SCAI may be already present before 30Y.

Purpose
To assess (1) the prevalence of SCAI, (2) the associated factors in SCAI development, and (3) the occurrence of clinical VT, in rTOF patients &lt;30Y.

Methods
From a database of 146 patients with rTOF or related lesions who underwent electroanatomical mapping (EAM) and programmed electrical stimulation (PES) between 2007 and 2022 for treatment of ventricular arrhythmias (VA), risk stratification or before pulmonary valve replacement (PVR), those aged &lt;30Y at time of procedure were selected and analysed.

Results
Of 146 rTOF patients, 55 (38%) were &lt;30Y (median 16Y [IQR 14-22]); 33/55 (60%) had TOF, 9/55 (16%) TOF with double outlet right ventricle (DORV), and 13/55 (24%) complex TOF variants, including 8 patients with pulmonary atresia with VSD, 2 patients with absent pulmonary valve, and 3 with other variations. Initial intracardiac surgical repair (median age 0.8Y [IQR 0.4-1.4]) was performed via a ventriculotomy in 10/55 (18%) after palliative shunts in 16/55 (29%). An RV to pulmonary artery (RV-PA) conduit was inserted during initial or early after (&lt;1Y) initial repair in 12/55 (22%). In 14/55 (25%) pulmonary valve replacement (PVR) was performed later in life (median age 10.1Y [IQR 2.7-14.3]). Five of 55 (9%) underwent EAM/PES after a spontaneous VA, 40/55 (73%) before PVR, and 10/55 (18%) for risk stratification. Monomorphic VT was inducible in 8/55 (15%), including 4/5 patients with spontaneous VT, and was proven related to a SCAI 3 in 7/8 (88%).
In 16/55 (29%) SCAI 3 could be identified; no other SCAI (1,2,4) was present. Of note, 9/16 (56%) of patients with SCAI 3 had initial RV-PA conduit repair/early PVR, in comparison with only 3/39 (8%) of patients without SCAI. In univariable analysis complex TOF (OR 6.8 [95% CI 1.8-26.4]), ventriculotomy (OR 5.3 [95% CI 1.2-22.3]), any prior PVR (OR 4.8 [95% CI 1.4-16.7]), and initial RV-PA conduit/early PVR (OR 15.4 [95% CI 3.3-71.8]) were significantly associated with SCAI 3. In multivariable analysis initial RV-PA conduit/early PVR remained the only independent predictor of SCAI 3 (OR 13.0 [95% CI 1.2-142.4]).

Conclusions
A SCAI 3 is present in 29% of rTOF patients &lt;30Y referred for EAM/PES and the dominant VT substrate for spontaneous and inducible VTs. RV-PA conduit placement during initial repair or early PVR (&lt;1Y after repair) is associated with SCAI 3 in young rTOF. Whether the early conduit/valve placement causes scarring at the infundibulum with consecutive slow conduction and/or whether the complex variants contribute to SCAI requires additional studies.