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

C. Gold (Frankfurt am Main)¹, F. Gausz (Szeged)², A. Vagvolgyi (Szeged)², J. Kupusovic (Frankfurt am Main)¹, F. Hecker (Frankfurt am Main)³, M. Miklos (Szeged)², V. Johnson (Frankfurt am Main)¹, A. Falagkari (Frankfurt am Main)¹, P. D. Culmann (Frankfurt am Main)¹, F. Post (Frankfurt am Main)¹, T. Szili-Torok (Szeged)², M. Vamos (Szeged)², D. Leistner (Frankfurt am Main)¹, R. Wakili (Frankfurt am Main)¹, J. W. Erath-Honold (Frankfurt am Main)^1
1Universitätsklinikum Frankfurt Med. Klinik III - Kardiologie, Angiologie Frankfurt am Main, Deutschland; ²Universität Szeged / Medizinische Klinik Ablg. Elektrophysiologie Szeged, Ungarn; ³Universitätsklinikum Frankfurt Klinik für Thorax-, Herz- und Thorakale Gefäßchirurgie Frankfurt am Main, Deutschland

Background
Sudden cardiac death (SCD) is still one of the main reasons for cardiovascular death.  To prevent SCD, implantation of a defibrillator (ICD) proved to significantly reduce mortality in well selected patients. To overcome some of the typical complications associated with transvenous (TV) ICDs, the subcutaneous ICD (S-ICD) has been developed. However, due to the extra-thoracic position of the S-ICD some studies claim that a higher BMI might be a risk factor for ineffective threshold testing and possibly ineffective shock discharge.

Purpose
The aim of this study was to investigate whether obesity is a risk factor for ineffective shock testing (DFT) during implantation and for ineffective or inadequate shock delivery during follow-up.

Methods
In this international, bicentric study (University Hospital Frankfurt, Germany, University of Szeged, Hungary), an all-comers collective for S-ICD implantation from November 2013 to Mai 2024 was retrospectively analyzed. 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 106 patients were included. Obese patients (n=27, mean BMI 35.4 ± 4.1) suffered from diabetes mellitus more often (34.6% vs. 12.7%; p=0.02) compared to non-obese patients (n=79, mean BMI 24.3 ± 2.8). There were no differences between the obese and non-obese group concerning age (50.1 ± 16.6 vs. 49.6 ± 16.7 years), disease etiology of cardiac disease (ischemic etiology: 40.7% vs. 39.7%; non-ischemic etiology: 37.0% vs. 43.6%) and gender (70% vs. 75% male).
66 non-obese (84%) and 22 obese patients (82%) underwent DFT at implantation. All patients underwent successful DFT at ≤80J, shock impedance was significantly higher in the obese patient group (57 ohm vs. 78 ohm; p=0.02) yielding also a significant correlation between higher BMI and higher shock impedance (r=0.44; p<0.001). During the mean follow-up time of 45.56 months there was no statically significant difference between the two groups regarding first shock effectiveness (64% vs. 50%; Hazard ratio (HR)= 1.01 (0.9-1.15); p=0.82) and the occurrence of inappropriate shocks (36% vs. 50%; HR= 1.00 (0.88-1.14); p=0.96). Of note, numerically more lead complications occurred in obese patients (n=0 vs. n=2), while patients with S-ICD and lower BMI had numerically more device-associated infections necessitating revision during follow-up (n=5 vs. n=0) both not reaching statistical significance.

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 more inappropriate shocks suggesting that S-ICD provides a safe and effective therapy option also for at-risk patients with higher BMI values. Nevertheless, these results warrant validation in greater patient cohorts.