Longitudinal high-voltage impedance patterns in the extravascular ICD
D Maroutsos, J Wasserlauf, M Metzl, L SinghAbstract
Background
The extravascular implantable cardioverter-defibrillator (EV-ICD) eliminates transvenous leads while providing limited pacing for tachycardia therapy and pause-prevention. Longitudinal high-voltage impedance (HVI) behavior and correlation with shock impedance during defibrillation threshold (DFT) testing have not been fully characterized.
Purpose
To describe HVI trends and evaluate the association between implantation HVI and shock impedance during defibrillation testing following EV-ICD implantation.
Methods
Serial HVI measurements were retrospectively assessed in consecutive patients undergoing EV-ICD implantation at a single-center. Defibrillation testing with ventricular fibrillation induction was performed at implant. Patients requiring system revision procedures were excluded. The association between implantation HVI and shock impedance was assessed using Spearman correlation and paired Wilcoxon testing. Longitudinal changes were evaluated using a linear mixed-effects model across predefined intervals: baseline, 0–3 weeks, 3 weeks–6 months, 6 months–1 year, and >1 year.
Results
Twenty patients (mean age 51.9 years; 25% female) were analyzed. Shock impedance during defibrillation testing was 64.5 ± 13.5 Ω (n = 20). Implantation HVI was 80.4 ± 30.7 Ω (n = 19) and strongly correlated with shock impedance (Spearman ρ = 0.93, p < 0.0001). Implantation HVI was significantly higher than shock impedance (mean difference 15.8 ± 21.6 Ω; p < 0.0001). Median follow-up was 9.7 months. HVI decreased at 0–3 weeks compared with baseline (estimate −22.3 Ω; 95% CI −37.0 to −7.6; p = 0.004). No significant differences were observed at later intervals (all p > 0.05) compared with implantation HVI, and no progressive impedance rise suggestive of system failure occurred.
Conclusion
Implantation HVI strongly correlates with shock impedance in EV-ICD recipients, with a systematic mean difference of 15.8 Ω. HVI decreases early after implantation but regresses toward baseline. These findings define expected post-implant impedance behavior and may assist in interpretation of EV-ICD diagnostics and system integrity.Correlation Between HVI and Implantation HVXLongitudinal HVI Trend