Defibrillation testing during S-ICD implantation: How relevant? Results from a multicenter study

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. INTRODUCTION: Defibrillation testing (DFT) is still recommended in patients with subcutaneous implantable cardioverter-defibrillator (S-ICD) to ensure proper detection of ventricular fibrillation and confirm effective defibrillation. Given the significant risk of complications, recent studies, are reconsidering the interest of the DFT in S-ICD. The purpose of this study was to assess the clinical "real-life" outcomes of DFT over a mid-term follow-up period after third-generation S-ICD implantation. METHODS AND RESULTS: 368 patients (pts) (47.9 ± 15.5 years old; male 72.8%) implanted with Generation 3 S-ICD system were included in this retrospective multicenter registry-based study. Mean left ventricular ejection fraction (LVEF) was 40.8% (primary prevention 56.1%). For 99.2% pts, S-ICD implantation was performed using the two-incision technique and intermuscular positioning of the generator was performed for all pts. 81% pts underwent ICD testing during implantation. Reasons for not performing DFT were: very low LVEF (3.5%), intracardiac thrombus (2.4%) and VF induction failure. In 2.2% (8 pts) DFT was unsuccessful, causes were: induction of ventricular tachycardias with rates falling below the shock zone for 3 pts while shocks were ineffective for 5 pts. One patient required revision for contralateral lead implantation, while sensing vector reprogramming and shock polarity modification were efficient for the others. The mean impedance was 68.4 (±14.7) Ω and time to shock therapy ranged from 10 to 33 s, with a mean of 16.7 (±4) s. A total of 36 appropriate shocks (10.1%) have been observed after a FU period of 11.02±8.8 months (1.8 shocks per patient, several shocks for 12pts, failure of the first shock for 5 patients). 17 patients (4.6%) underwent S-ICD system extraction. The reasons were pocket site complication (7 pts), pacing indication for cardiac resynchronization therapy or bradycardia (3 pts), and S-ICD lead dysfunction (4 pts). Extraction after heart transplant was needed in 3 pts. Among the 4 pts explanted for system dysfunction, only one patient had a DFT during implantation. After a mean follow-up of 19±12.1 months, the mortality rate was 3.8% (no S-ICD-related deaths were reported). There was no significant difference between the 2 groups of pts with and without DFT testing (p=0.629). CONCLUSION: The DFT remains for the moment highly recommended during S-ICD implantations. Results from randomized studies are still needed to confirm the relevance of DFT during S-ICD implantation.