GENOTYPE, PHENOTYPE AND OUTCOMES OF PATIENTS WITH HYPERTROPHIC CARDIOMYOPATHY REFERRED FOR ABLATION OF VENTRICULAR TACHYCARDIA.

Background:
Sustained monomorphic ventricular tachycardia (SMVT) is the most common ventricular arrhythmia (VA) subtype in hypertrophic cardiomyopathy (HCM) patients with ICD. Data on catheter ablation is limited, focusing on non-genotyped patients with mild hypertrophy or apical aneurysms.

Purpose:
This study describes the genotype, phenotype, and outcomes of consecutive HCM patients referred for CA ablation of refractory SMVT.

Methods and Results:
Among 976 patients referred for SMVT ablation between 01/2016 and 10/2023, nine had an HCM phenotype. Most (8/9) exhibited dominant septal hypertrophy; none had LV outflow tract obstruction, and only one had an apical aneurysm. The median max wall thickness was 25 mm, and the median LVEF was 34%. Six patients had a class IV/V variant in the myosin-binding protein C (MYBPC3) gene, while no disease-causing variant was identified in three. All MYBPC3 mutation carriers presented with electrical storm/incessant VT refractory to antiarrhythmic drugs (AAD), including amiodarone. Four of these patients required multiple ablations and additional interventions like transcoronary alcohol-ablation, surgical resection, and radiotherapy. After a median follow-up of 25 months, all MYBPC3 variant carriers experienced VT recurrence; three died, and one underwent heart transplantation. In contrast, patients without class IV/V variants had better outcomes, with only one VT recurrence and one death 24 months post-CA.

Figure 1 shows the disease course in the patient series. 

Conclusions:
Only 1% of patients referred for SMVT ablation at a high-volume center had an HCM phenotype. A MYBPC3 variant was found in 67%, with 89% having severe hypertrophy. VT-free survival is particularly poor in MYBPC3 variant carriers, underscoring the need for early advanced heart failure management, including consideration of heart transplantation.