Clinical profile and outcomes of S-ICD and TV-ICD recipients in HCM: insights from a real-world cohort

Background

Implantable cardioverter-defibrillators (ICDs) are a cornerstone of sudden cardiac death (SCD) prevention in patients with hypertrophic cardiomyopathy (HCM). The subcutaneous ICD (S-ICD) provides an extravascular alternative to the traditional transvenous system (TV-ICD), yet comparative evidence specific to the HCM population remains scarce.

Aims

To characterize baseline differences between S-ICD and TV-ICD recipients and to evaluate potential variations in their clinical outcomes.

Methods

We performed a retrospective cohort study including all patients with a diagnosis of HCM followed at our center, up to November 2025. Demographic, echocardiographic, and clinical data were systematically reviewed. Outcomes of interest included appropriate ICD therapies, and inappropriate shocks, cardiac transplantation and all-cause death. Follow-up time was calculated from device implantation to either death or last documented clinical contact. Group comparisons were conducted using chi-square tests and t-tests, and multivariable Cox regression was applied to assess the independent association between device type and major outcomes.

Results

A total of 198 HCM patients underwent ICD implantation, of whom 66 (33%) received an S-ICD and 132 (67%) a TV-ICD. S-ICD recipients were younger (42 ± 17 vs. 56 ± 17 years, p < 0.001) and exhibited greater maximal left ventricular wall thickness (22 ± 8 vs. 19 ± 5 mm, p = 0.004). They also had a lower prevalence of cardiovascular risk factors (e.g., diabetes: 5% vs. 24%, p = 0.001) and atrial fibrillation (32% vs. 48%, p = 0.034). Additionally, S-ICD patients were less frequently prescribed anti-arrhythmic drugs (8% vs. 20%, p = 0.036).

Indications for primary versus secondary prevention did not differ between groups (86% vs. 84%, p = 0.834). Likely pathogenic / pathogenic genetic test results were observed in 36 (54.5%) S-ICD and 61 (46.2%) TV-ICD recipients (p = 0.294). Clinical outcomes were similar across device types, including heart transplantation (9% vs. 8%, p = 0.784), appropriate ICD therapies (6% vs. 8%, p = 0.778), and inappropriate shocks (11% vs. 8%, p = 0.607). All-cause mortality was similar albeit numerically higher in TV-ICD recipients (8% vs. 14%, p = 0.247). Infections occurred in 1 (1.5%) S-ICD recipient and 2 (1.5%) TV-ICD recipients (p = 1.00). Other clinical, echocardiographic, and electrocardiographic parameters showed no significant differences between the groups.

Conclusions

HCM patients implanted with an S-ICD and TV-ICD had similar clinical outcomes, albeit all-cause death was numerically higher in TV-ICD – almost double that of S-ICD recipients. S-ICDs were more frequently selected for younger patients with fewer comorbidities. Our findings highlight the contemporary pattern of preferential use of S-ICD in younger individuals with lower disease burden in a real-world cohort of patients with HCM.For image description, please refer to the figure legend and surrounding text.