A 10 J shock impedance in sinus rhythm correlates with a 65 J defibrillation impedance during subcutaneous defibrillator implantation using an intermuscular technique

Abstract

Introduction: Defibrillation testing (DT) is recommended during the subcutaneous defibrillator (S-ICD) placement. We sought to compare 10 J shock impedance in sinus rhythm (SR) with 65 J defibrillation impedance and evaluate device position on a postimplant chest X-ray (CXR) using an intermuscular (IM) technique.Methods: Consecutive S-ICD implantations between 12/2019 and 12/2020 at The Ohio State University were reviewed. All implantations were performed using a two-incision IM technique. Standard DT with 65 J shock and 10 J shock in SR were performed unless contraindicated. The PRAETORIAN score was calculated based on CXR.Results: A total of 37 patients (age: 47.2 ± 15.8 years old, male: n = 26 [70.3%], body mass index: 30.1 ± 6.7 kg/m 2 ) underwent IM S-ICD implantation, and of those, 27 (73%) underwent both 65 J shock and 10 J shock in SR. The coefficient of determination (R 2 ) between 10 J shock impedance and 65 J shock impedance was 0.84. The mean of an impedance difference was 1.6 ± 4.8 Ω (minimum -11 and maximum 8). Postimplant CXR was available for 33 out of 37 patients (89.2%). The PRAE-TORIAN score was less than 90 in all patients and the mean score was 32.7 ± 8.8. Conclusion:We demonstrated that 10 J shock impedance in SR correlated well with 65 J defibrillation impedance during IM S-ICD implantation. An IM implantation technique provides excellent generator location on postimplant CXR. The IM technique combined with 10 J shock in SR may be sufficient to predict and ensure the defibrillation efficacy of the S-ICD.

S-ICD Implantation "Tips and Tricks"

“…In patients with contraindications for a DFT, a 10 J test shock with no VF induction is considered a surrogate of DFT, as it allows for true high-voltage impedance measurement (and not its low-voltage approximation). That method cannot confirm appropriate VF sensing and detection, and the value of impedance measurement only is disputable [ 99 , 100 ], as it may vary with the patient’s body composition and built, chest fluid content (e.g., pleural effusion) and device location. There are several reports available suggesting that DFT testing may be safely waived in S-ICD patients [ 101 , 102 ], but more conclusive data are awaited from the PRAETORIAN-DFT trial, which was designed to investigate the possibility of substituting the DFT with PRAETORIAN score calculation only [ 103 ].…”