Long-term changes in high-voltage impedance of defibrillating leads

Area of Science:

• Cardiovascular Medicine
• Biomedical Engineering
• Medical Device Technology

Background:

• The maturation of high-voltage lead impedance (HVLI) in implantable cardioverter-defibrillators (ICDs) is not well understood.
• Impedance is critical for determining delivered energy and defibrillation effectiveness.
• Understanding HVLI maturation is essential for maintaining optimal defibrillation threshold (DFT) safety margins.

Purpose of the Study:

• To investigate the maturation patterns of high-voltage lead impedance (HVLI) in patients with implantable cardioverter-defibrillators (ICDs).
• To determine the frequency and magnitude of HVLI changes over time.
• To compare HVLI maturation with different superior vena cava (SVC) coil configurations.

Main Methods:

• Analysis of high-voltage shock diagnostic data from 515 ICD recipients over 24 months.
• Recording and normalization of HVLI values relative to implant values.
• Calculation of the percentage of patients with HVLI changes (> or =6 Omega) and comparison of SVC coil ON versus OFF configurations.

Main Results:

• 41% of patients experienced a HVLI change of > or =6 Omega more than 3 months post-implant.
• The majority (67%) of these changes involved an increase in impedance.
• For the RV Coil-to-Can configuration with SVC OFF, HVLI increased by 8 Omega within 6 weeks and stabilized thereafter.

Conclusions:

• Significant HVLI maturation occurs in a substantial portion of patients within 3 months.
• Observed HVLI changes (6-12 Omega) can alter shock waveform characteristics, potentially impacting DFT.
• These impedance fluctuations may contribute to the reported increase in DFT over time and necessitate waveform retuning.