Background: 

The safety and efficacy of the subcutaneous implantable cardioverter-defibrillator (S-ICD) has been proven in various clinical trials. Due to the intermuscular device placement, higher shock energy is required for effective treatment of ventricular arrhythmia. Previous studies have shown reduced shock efficacy in device replacement procedures, possibly due to device encapsulation associated with dwelling time of the device. Therefore, in case of severe capsulation of the device, capsulectomy became a part of the device replacement procedure in our center. In this study we analyzed the results of intraoperative testing before and after capsulectomy measured by results of shocking impedance. 

Methods: 

Between January 2018 and November 2022, a total of 68 consecutive patients underwent S-ICD device replacement in our center. Pre-operative shock resistance was determined either through recent therapy deliveries or by 10J test shock prior to the first incision during device replacement. Device replacement was performed according to international standards. In case of severe capsulation, additional capsulectomy was performed. Defibrillation testing was performed by standard ensuring system functionality at 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 received their S-ICD for primary prevention (69%). Defibrillation testing with 65 J at the time of 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 at the initial implantation (p=0.013). Capsulectomy of the S-ICD pocket resulted in a significant lowering of the shock impedance to 83±23 Ω as compared to the 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 the hospital stay, etc.) were observed in short term follow-up and patients could be discharged as planned. 

Conclusion: 

Capsulectomy of the S-ICD pocket appears to be a safe and effective way to reduce shock resistance which has proven to be a predictor of successful defibrillation in testing as well as 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. However, prospective trials addressing the optimal device replacement strategy are warranted.