44 High system impedance and clinical outcomes following subcutaneous implantable cardioverter-defibrillator implantation: a single-centre retrospective analysis
Year: 2026
Type: conference-paper
Study design: Observational Study
Abstract: Background Subcutaneous implantable cardioverter-defibrillators(S-ICDs) are an attractive alternative to transvenous(TV) systems, particularly for younger patients who do not have a pacing indication. Shock impedance at implant is measured with a defibrillation threshold test(DFT). System impedance, a surrogate for shock impedance, can be measured at implant and at follow-up. A rise in impendence above the recommended threshold(>100Ω) may result in failure of the device to reliably deliver therapy. Purpose We aimed to conduct a retrospective analysis of patients implanted with a S-ICD in a single tertiary referral centre with a particular focus on impedance values. We examined the incidence of high impedance(>100Ω) on follow-up. Furthermore, we determined the proportion of patients who had a revision of S-ICD or TV-ICD because of high impedance values. Methods Data was collected on patients implanted with a S-ICD from 2014-2025 using electronic patient records. Patient characteristics, implant procedure details, impedance values, repeat procedures and mortality were examined. Descriptive statistics used mean(+/- standard deviation) or median(interquartile range) depending on data normality. Proportions are reported as n(%). Results 186 patients were eligible for inclusion. Patient characteristics and ICD indication are displayed in table 1. Shock impedance at implant was 70.4Ω(+/-14.1) and system impedance was 64Ω(+/-12.7) (table 2). System impedance on follow-up was 82.4Ω(+/-26). At 4.7(3.3-6.5) years from implant, 39 patients(21%) had impedance values >100Ω. Of these, 8 underwent a repeat procedure due to high impedance; 2(1.1%) had S-ICD revision/re-implant and 8(4.3%) had a TV-ICD implanted. One patient had both. 30 patients(16.1%) with high impedance were monitored without immediate intervention planned. Conclusions High system impedance is commonly encountered during S-ICD follow-up in the real-world setting. This may result in unsuccessful shocks, repeat procedures and avoidable risk. It will be important to identify predictors of rising impedance, so that an informed decision can be made at the time of ICD implant.
Source: Heart
Language: English
Subfield: Cardiology and Cardiovascular Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W7221822014