Linking implantation and follow-up impedance to spontaneous shock in subcutaneous implantable cardioverter defibrillator patients
L Smit, M Rienstra, A H MaassAbstract
Introduction
The Subcutaneous Implantable Cardioverter Defibrillator (S-ICD) has become an important treatment option for prevention of sudden cardiac death. High-voltage impedance (HVI) measurement is performed at implantation via defibrillation threshold testing (DFT), with impedance playing a critical role in predicting conversion success. There is conflicting evidence for the evolution of HVI if re-tested during device replacement. In recent years, during follow-up low-voltage shock impedance (LVI) measurement can be performed.
Purpose
The primary objective is to determine whether DFT impedance is related to the impedance measured years later during spontaneous shock events. Additionally, we evaluate whether LVI measured during follow-up is related to HVI.
Methods
We included 122 patients undergoing S-ICD implantation in this single-centre study in the period from April 2010 until October 2025. HVI measurements were collected at DFT testing and spontaneous shocks. LVI measurements were collected at follow-ups. A retrospective analysis of S-ICD patients receiving intraoperative DFT was performed. Spearman's rank correlation was used to assess the relationship between HVI at DFT and LVI to HVI at spontaneous shock.
Results
This study included a total of 122 patients, of which 39.3% female and mean age of 41 years ± 16 years. 27 patients (22.1%) received a spontaneous shock during follow-up. Median HVI at DFT was 72.0 Ω (61.5.0–83.0). Median LVI at follow-up was 70.0 Ω (50.0–75.0). Median HVI at spontaneous shock was 62.0 Ω (48.0–70.0). There was a strong positive correlation between impedance at DFT and at spontaneous shock (r(df) = 0.66, p = 0.001) (graph 1). There was also a strong positive correlation between LVI at follow-up and HVI at spontaneous shock (r(df) = 0.69, p = 0.005) (graph 2).
Conclusion
To conclude, DFT impedance is related to impedance during spontaneous shock and LVI at follow-up is related to HVI. These findings support testing and optimizing DFT HVI at implantation, and the use of LVI testing during follow-up, given their association with spontaneous shock impedance.Figure 1.Figure 2.