Association Between Slowly Conducting Anatomical Isthmuses and Ventricular Tachycardia Inducibility in Tetralogy of Fallot.

Background: Catheter ablation of sustained monomorphic ventricular tachycardia (SMVT) guided by the identification of slowly conducting anatomical isthmuses (SCAIs) has been proposed to mitigate the risk of ventricular tachycardia in tetralogy of Fallot (TOF). However, the prevalence and clinical significance of SCAI remain uncertain.

Objectives: This study aimed to assess the association between SCAI and SMVT inducibility in patients with TOF.

Methods: A multicenter international cohort with retrospective (2017-2021) and prospective (commencing 2021) components enrolled patients with TOF referred for electrophysiological study before transcatheter pulmonary valve replacement. The proportion with SCAI and its association with SMVT inducibility were analyzed.

Results: A total of 162 patients (mean age 39.5 ± 14.2 years; 57.4% male) were included. SMVT was induced in 42 (25.9%) patients, and ≥1 SCAI was present in 76 (46.9%) patients. The prevalence of SCAI was higher in patients with inducible SMVT (78.6% vs 31.1%; P < 0.001). However, 21.4% of patients with inducible SMVT had normally conducting anatomical isthmus (14.3%) or a non-anatomical isthmus substrate (7.1%). The area under the curve of SCAI in predicting SMVT inducibility was 0.71 (sensitivity 78.6%; specificity 64.2%). Although SCAI was independently associated with SMVT (OR: 6.4; 95% CI: 2.6-18.2), the association with other clinical parameters improved prediction of SMVT inducibility.

Conclusions: SCAI is highly prevalent in patients with TOF and is associated with inducible SMVT. However, the proportion of SCAI in noninducible patients is substantial, and some inducible patients have no SCAI. These findings suggest that SCAI alone is insufficient for arrhythmia management decisions, highlighting the need for an integrative approach combining electrophysiological study with other clinical parameters.