The impact of obesity on defibrillation threshold testing, shock effectiveness and inadequate shock rate in a bicentric cohort of S-ICD recipients

Abstract Background Sudden cardiac death (SCD) remains a leading cause of cardiovascular mortality. The implantation of a defibrillator (ICD) proved to significantly reduce mortality in well selected patients. To overcome typical complications associated with transvenous (TV) ICDs, the subcutaneous ICD (S-ICD) has been developed. However, due to the extra-thoracic position, some studies claim that a higher BMI might be a risk factor for ineffective defibrillation threshold testing (DFT) and ineffective shock discharge. Purpose Aim of this study was to investigate whether obesity is a risk factor for ineffective DFT testing at implantation and for ineffective or inadequate shock delivery during follow-up. Methods This international, bicentric study, retrospectively analyzed an all-comers collective for S-ICD implantation from November 2013 to Mai 2024. The patient cohort was divided in two groups due to their respective BMI (<30 kg/m² and ≥30 kg/m²) based on the WHO definition for obesity. Results A total of 120 patients were included. Obese patients (n=30, mean BMI 35.0±4.1) suffered from diabetes mellitus more often (31% vs. 14%; p=0.02) compared to non-obese patients (n=90, mean BMI 24.0±2.9). Patient groups were comparable in age (51.1±16.7 vs. 50.3±16.6 years), cardiac disease etiology (ischemic: 37% vs. 42%; non-ischemic: 37.0% vs. 42%) and gender (70% vs. 75% male). 76 non-obese (86%) and 25 obese patients (83%) underwent DFT at implantation. Mean shock energy of first successful shock was 65J in both groups, whereas shock impedance was significantly higher in the obese patient group (63 vs. 73 ohm; p=0.02) with a significant correlation between higher BMI and higher shock impedance (r=0.37; p<0.001, see figure 1). Consequently, mean PRAETORIAN score was higher in the obese group, proposing a mean intermediate risk for failure to convert in this group (123 vs. 53; p=0.04, see table 1). During the mean follow-up time of 46 months (± 37), no significant difference was found between both groups regarding first shock effectiveness (100% vs. 100%) and the occurrence of inappropriate shocks (10% vs. 10%). There was a trend towards more lead complications in obese patients (n=5 vs. n=4; OR 3.8(0.946-15.3, p=0.06)), while patients with lower BMI had more device-associated infections necessitating revision during follow-up (n=5 vs. n=0), both not statistically significant. Conclusion This retrospective bicentric study demonstrates that obesity is associated with significantly higher shock impedance during DFT at S-ICD implantation while shock efficacy remains stable during implantation and subsequent follow-up. Obese patients did not experience ineffective appropriate shock despite higher PRAETORIAN scores nor more inappropriate shocks compared to non-obese patients, suggesting that the S-ICD provides a safe and effective therapy option also for at-risk patients with higher BMI values.