Can we predict if defibrillation testing of a subcutaneous implantable cardioverter defibrillator can be avoided safely at device replacement?

Abstract Background Current guidelines recommend to perform a defibrillation test (DFT) when a subcutaneous implantable cardioverter defibrillator replacement is performed. For transvenous ICD systems there is evidence that this can be safely omitted but evidence is lacking for patients that have a subcutaneous implantable cardioverter defibrillator implanted. Purpose To evaluate pre-procedural parameters that can predict the outcome of the DFT so this may safely be avoided. Methods A retrospective multicenter analysis of subcutaneous implantable cardioverter defibrillator patients undergoing a device replacement with or without DFT was performed. Results The cohort included 151 patients: 121 male, age 60.9±16.4 year, LVEF 40.5±7.1, primary prevention 65%. In total 176 device replacements where included. At first implant 136 patients ( 92.5%) had a DFT with a single 65J shock success rate of 93.4%. At first implant the average shock impedance was 77(±21). A Praetorian scores of 30-90 was achieved in 71 (60.2%) of the patients. Only 7 (5,9%) had a score ≥ 150 but still successful DFT. During first replacement 55% of the patients (83) underwent DFT testing with a 90,4% single shock success rate. Only 8 patients needed a second DFT. At the second replacement 9 Patients (36%) were tested with a single shock success rate of 100%. X rays were made in 55 (36,4%) and 5 (20,8%) before first or second replacement. X rays showed that 45 patients (84,9%) had a stabile lead position at first replacement and 3 patients (60%) at second replacement. A unstable position might influence the impedance or the Praetorian score in a negative way on shock conversion capability. Average shock impedance was 90 Ohm(± 25) at first replacement and 72 (±22) at second replacement. A high impedance lowers the power of the delivered shock and influence the efficacy of the DFT. More than 60% of the patients had a Praetorian scores of 30-90. Only 3 patients ( 5.9%) at first replacement had a score of ≥ 150. The praetorian score estimates the risk of conversion failure. A praetorian score of ≥ 90 has a positive predictive value of 25% for failed DFT. Conclusion It is feasible to safely avoid the DFT test if certain precautionary measures are performed before the device replacement. Comparing X-ray, Praetorian score and impedance measurements with the values of first implant can assist in making the decision of avoiding the DFT testing.