Ventricular Tachycardia Substrates in Children and Young Adults with Repaired Tetralogy of Fallot.
Wallet J, Kimura Y, Blom NA, Jongbloed MRM, Bertels RA, Hazekamp MG, Zeppenfeld K.JACC Clin Electrophysiol. 2024 Dec;10(12):2613-2624. doi: 10.1016/j.jacep.2024.07.016. Epub 2024 Sep 25.PMID: 39340504
Take-home Points:
- Slow conducting anatomical isthmuses (SCAI 3) is present in 29% of repaired ToF patients < 30 years of age.
- In young patients, the presence of SCAI 3 was associated with complex ToF variants and potentially related to type and timing of surgical repair.
- Ablation failures in this study resulted because of artificial material (conduit or valves) overlying the ablation target.
- Pre-PVR electrophysiologic evaluation and potential ablation is supported by the current study
Commentary By:
Dr. Timothy Roberts (Melbourne, Australia), section editor of ACHD Journal Watch
Introduction
Patients with surgically repaired tetralogy of Fallot (rToF) remain at risk for late appearing ventricular tachycardia (VT) and sudden cardiac death, despite early surgical repair. Slow conducting anatomical isthmuses (SCAI) bordered by valve annuli, patch material, and ventricular incisions, are the most common substrates for VT in patients with rToF. While the occurrence of VT and sudden cardiac death increases after age 30, and significantly more likely after age 45, there is a paucity of data whether the same electroanatomic substrates exist at a much younger age.
This study was conducted at the Leiden University Medical Center (Leiden, Netherlands) and sought to evaluate the prevalence of SCAIs in rToF patients under 30 years of age and identify associated risk factors. Since 2007, it has been the study group’s institutional practice to perform electroanatomical mapping (EAM) and programmed electrical stimulation (PES) in all patients undergoing surgical or transcutaneous pulmonary valve replacement (PVR) in rToF patients ≥ 8 years of age.
The study population consisted of any rToF patient < 30 years of age who underwent EAM and PES between 2005 and 2022 for a history of spontaneous ventricular arrhythmia, pre-PVR evaluation, or VT risk stratification per their institutional practice. A total of 55 patients (55% male) were included in the study cohort. The median age at electrophysiological evaluation was 15.8 years (IQR: 13.8-21.8 years), of whom 40 (73%) were included as part of pre-PVR evaluation.
SCAI 3 (between the pulmonary annulus and the ventricular septal defect patch; defined as < 0.5 m/s across the anatomic isthmus) was present in 16 (29%) patients, 11 of whom were included as part of the pre-PVR evaluation. SCAI 3 was more often present in patients with complex ToF variants (those with pulmonary atresia or absent pulmonary valve), those in whom a ventriculotomy was performed at their initial repair, and those with an initial repair consisting of a RV-PA conduit or requiring early PVR. Surgical cryoablation was performed in all 11 pre-PVR patients identified with SCAI 3, and the remaining 5, who were included in the cohort because of a history of spontaneous VT, underwent radiofrequency catheter ablation (RFCA). The central illustration below summarizes these findings:
Two catheter procedures were unsuccessful because of an overlying PVR. One postoperative patient who underwent intraoperative cryoablation was found to have a persistent SCAI 3 at their post-surgical evaluation. For this case, the isthmus could not be blocked by additional RFCA because of an overlying conduit. All these patients with unsuccessful block of SCAI 3 underwent ICD implantation.
In their discussion, the authors note that SCAI 3 in this young cohort was present in 29% of the study population, which is not so different than in prior studies showing a prevalence of 31 to 38% for middle-aged rToF patients. This suggests that additional factors apart from aging contribute to the development of SCAIs. In this study, 9 of 16 patients (56%) with SCAI 3 were not inducible for monomorphic sustained VT, compared with the 7% non-inducible rate in older patients. This is a potential area for future investigation which may impact the value of PES without EAM for risk stratification in young patients.
Conclusion:
The current study was limited by its small cohort, retrospective design, and observational analysis. Even so, the study still draws important conclusions for an at-risk population of congenital patients, in whom early interventions can have potentially life-altering impacts. When considering the implications on clinical practice, at their own institution, the authors have implemented EPE before PVR in all patients, including those < 30 years of age. They support this approach by highlighting that all ablation failures in their study were from overlying artificial material, and the high prevalence of SCAI 3 in their study group. They add that preventative ablation of SCAI 3 at the time of reoperation may be beneficial, given that in those patients who were inducible for VT during EPE, SCAI 3 was the critical isthmus in 88% of cases.
