Subcutaneous ICD therapy across underlying cardiac diseases in paediatric and young adult patients: insights from the european SIDECAR registry

Background Subcutaneous implantable cardioverter-defibrillators (S-ICDs) are increasingly used in paediatric and young adult patients as an alternative to transvenous systems, particularly in the presence of complex anatomy or long-term vascular risk. However, data comparing S-ICD performance across different underlying cardiac diseases remain limited. The objective was to evaluate the safety and efficacy of S-ICD therapy according to the underlying cardiac condition in patients enrolled in the SIDECAR registry. Methods The SIDECAR registry included consecutive paediatric and young adult patients who received an S-ICD across 12 European centres. Patients were stratified by underlying diagnosis: congenital heart disease (CHD), cardiomyopathy (CMP), channelopathy (CHAN), and idiopathic ventricular fibrillation (IVF). Outcomes included appropriate and inappropriate shocks (IAS), and complications. Results A total of 223 patients were analysed: 31 (14%) CHD, 119 (53%) CMP, 39 (18%) CHAN, and 34 (15%) IVF. Median follow-up was 28 months. Rates of appropriate shocks, IAS, and complications were 25.7% (95% CI: 17.5-33.9), 19.6% (95% CI: 12.2-27.0), 5.0% (95% CI: 1.6-8.4) at 5 years, respectively. No significant difference in freedom from appropriate shock (log-rank p=0.593), IAS (p=0.897) or complication rate (p=0.793) was observed between subgroups. The mechanism of IAS differed across groups, with T-wave oversensing predominating in CHD and CMP, non-cardiac oversensing in CHAN and supraventricular tachyarrhythmias in IVF. Conclusions In this large paediatric S-ICD cohort, outcomes were consistent across different cardiac aetiologies, supporting its broad applicability in young patients with inherited or structural heart disease.