Capsulectomy: a safe and effective way to lower shock impedance in S-ICD replacement procedures

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. BACKGROUND: The safety and efficacy of the subcutaneous implantable cardioverter-defibrillator (S-ICD) has been proven in various clinical trials. Due to intermuscular device placement, higher shock energy is required for effective treatment of ventricular tachyarrhythmia. High shock impedance is a risk marker for ineffective defibrillation. Previous studies have shown reduced shock efficacy in device replacement procedures, possibly due to fibrous encapsulation of the device associated with dwelling time of the system. Therefore, in case of significant capsulation, capsulectomy became part of device replacement procedure in our center. In this study we analyzed the results of intraoperative testing before and after capsulectomy measured by results of high-voltage impedance. PURPOSE: Aim of our study was to show that removal of the fibrous capsulation can help to reduce high voltage impedance without relevant perioperative adverse events at the device replacement procedure. METHODS: Between January 2018 and November 2022, a total of 68 consecutive patients underwent S-ICD device replacement in our center. Pre-operative high-voltage impedance was determined either through recent therapy deliveries or by a 10J test shock immediately before device replacement. Device replacement was performed according to international standards. In case of significant capsulation, additional capsulectomy was performed. Defibrillation testing was routinely performed by the end of the procedure in the absence of contraindications. RESULTS: Of 68 patients, 81% were male, mean age at device replacement was 55 ± 17 years. Most patients were implanted for primary prevention (69%). Defibrillation testing with 65 J at initial device implantation was successful in 87% of patients. Mean dwelling time of the S-ICD System was 61 months (±19 months). Shock impedance increased significantly to 98±33 Ω vs. 80±20 Ω (p=0.013) at initial implantation. Capsulectomy of the S-ICD pocket resulted in a significant decrease of high-voltage impedance to 83±23 Ω as compared to measurement prior to replacement (p=0.03). Defibrillation testing was successful in all patients. First shock efficacy with 65 J was 92%. No acute complications (defined as significant bleeding, prolongation of hospital stay, etc.) were observed in short term follow-up and patients could be discharged as planned. CONCLUSION: Capsulectomy of S-ICD pocket appears to be a safe and effective way to reduce shock impedance which has proven to be a predictor of successful defibrillation in testing as well as in spontaneous episodes. Despite the additional step during device replacement, no complications were observed in our study. Randomized trials regarding defibrillation testing during first implantation are ongoing. Trials addressing the optimal device replacement strategy however are warranted.