Defibrillation failure in patients undergoing replacement of subcutaneous defibrillator pulse generator

BACKGROUND Defibrillation threshold (DFT) testing is commonly performed in patients undergoing subcutaneous implantable cardioverter-defibrillator (S-ICD) implantation. Growing evidence indicates that successful DFT testing correlates with the technique used for implantation of the defibrillation lead and pulse generator. However, evidence on whether DFT testing should be performed in patients undergoing S-ICD pulse generator replacement is lacking. OBJECTIVE The purpose of this study was to determine the outcome of DFT testing in patients undergoing replacement of an S-ICD pulse generator. METHODS A total of 357 S-ICD implantations were performed between November 2010 and July 2019. Twenty-five consecutive patients underwent S-ICD replacement between 2015 and 2019. Clinical data, perioperative medication, technical measurements, and PRAETORIAN score were assessed and grouped according to the outcome of DFT testing. RESULTS In 5 of 25 patients (20%), induced ventricular fibrillation was not successfully terminated after the first or second 65-J shock after pulse generator replacement with need for external defibrillation. Repositioning of the pulse generator and/or capsulectomy at the pocket site were necessary to achieve effective DFT with 65 J in all cases. Shock impedance increased in all patients at the time of pulse generator replacement compared to first implantation and was significantly higher in patients with ineffective DFT (119 +/- 17 Omega vs 93 +/- 26 Omega; P = .03). Otherwise, no differences in clinical characteristics, comorbidities, body mass index, intraoperative medication, or PRAETORIAN score were predictive of defibrillation failure. CONCLUSION The high proportion of patients with DFT failure after S-ICD pulse generator replacement indicates that DFT testing is mandatory to ensure safe function of the S-ICD.