Long‐Term Changes in High‐Voltage Impedance of Defibrillating Leads

Abstract

The maturation of the high-voltage impedance (HVLI) of defibrillating leads has not been explored thoroughly. Since impedance influences the charge, current, and energy delivered to the heart in both fixed pulse-width and fixed tilt implantable cardioverter-defibrillator (ICD) waveforms, changes in HVLI might have an effect on the defibrillation threshold. This analysis examined the maturation of defibrillation lead HVLI. The data were collected in 515 recipients of ICDs capable of storing high-voltage shock diagnostics, including HVLI. Data with constant superior vena cava (SVC) coil configuration (coil ON or OFF) were collected for up to 24 months. HVLI values were recorded, plotted, and normalized by the value at implant; the percentage of patients in whom HVLI increased or decreased by > or =6 Omega was calculated, and the maturation of leads with SVC ON versus OFF was compared. A > or =6 Omega increase or decrease in HVLI was observed in 41% of patients more than 3 months after ICD implant, with the magnitudes as follows: 6-7.5 Omega change = 16%, 8-9.5 Omega= 11%, 10-11.5 Omega= 6%, and > or =12 Omega= 8%. In this subgroup, 67% of patients showed an increase in impedance, and the remaining 33% of patients showed a decrease. For ICD-programmed SVC OFF, the right ventricular (RV) Coil-to-Can HVLI increased by 8 Omega after 6 weeks and did not significantly change thereafter. HVLI changed significantly in 41% of leads after 3 months. The HVLI trend of the RV Coil-to-Can configuration appeared to be similar to the SVC Coil/Can-to-RV and Coil-to-Can configurations. Changes in HVLI of 6-12 Omega will alter the characteristics of the shock waveform and could require retuning of the waveforms to maintain adequate DFT safety margin. If re-tuning the shock waveforms is not performed, these HVLI changes have the potential to result in elevated DFT. These HVLI changes may partially account for the 15% increase in DFT over time reported in the literature.