The causes of inappropriate shocks differ between the subcutaneous and extravascular implantable cardioverter-defibrillators

Introduction Subcutaneous implantable cardioverter defibrillators (S-ICDs) and extravascular-implantable cardioverter-defibrillators (EV-ICDs) have emerged as alternative defibrillation options to avoid the complications of transvenous leads. However, their sensing electrodes' extracardiac locations may increase their susceptibility to oversensing which may cause painful, and potentially arrhythmogenic, inappropriate shocks (IAS). Objective The objective of this study was to compare the causes of IAS between the S-ICD and EV-ICD. Methods The FDA’s Manufacturer and User Facility Device Experience (MAUDE) database was queried for IAS reports submitted by the two manufacturers from January 2024 to September 2025. Outcomes included 1) oversensing noise, T-waves oversensing (TWOS), P-waves oversensing (PWOS), and electromagnetic interference (EMI), and 2) misinterpreting supraventricular tachycardia (SVT), atrial fibrillation (AF), and sinus tachycardia (ST) as ventricular tachycardia (VT) or ventricular fibrillation (VF). Results The search found 1,900 S-ICD and 68 EV-ICD IAS reports. Oversensing of unspecified noise and TWOS caused significantly more IAS by S-ICDs vs EV-ICDs (RR = 2.13, CI: 1.24-3.68, p<0.01; RR = 8.88, CI: 2.26-34.84, p<0.01, respectively), while IAS due to misinterpreting SVT, AF, and ST as VT/VF (RR = 0.32, CI: 0.24-0.44, p<0.01), PWOS (RR = 0.1, CI: 0.05-0.21, p<0.01), and EMI (RR = 0.15, CI: 0.09-0.25, p<0.01) were more common with EV-ICDs than SC-ICDs (Table 1, Figure 1). Oversensing of myopotential noise was not different between the two groups. Only with S-ICD, sense B-noise, air entrapment, and intrinsic morphology changes were causes of IAS (Table 1). In 8 S-ICD and 1 EV-ICD reports, there was more than one cause of IAS. Conclusion The causes of IAS are significantly different between S-ICDs and EV-ICDs. The incidence and reasons for these major differences as well as the long-term clinical consequences of these differences require further investigation. If confirmed, this may assist in individualizing device selection to patient-specific risk profiles and encourage targeted follow-up strategies.