Increase in defibrillation threshold in non-thoracotomy implantable defibrillators using a biphasic waveform

Area of Science:

• Cardiology
• Biomedical Engineering
• Electrophysiology

Background:

• Previous studies indicated a chronic increase in defibrillation threshold (DFT) with monophasic waveforms in non-thoracotomy implantable cardioverter-defibrillator (ICD) systems.
• The cause of this DFT increase remained unclear, with possibilities including the lead system or waveform characteristics.

Purpose of the Study:

• To investigate whether the observed chronic increase in DFT is related to the lead system or the specific waveform used.
• To evaluate the chronic DFT in patients receiving an ICD capable of delivering biphasic waveforms using the same lead system.

Main Methods:

• A prospective study involving 25 patients implanted with an ICD delivering biphasic waveforms.
• Defibrillation threshold measurements were performed at implant and at 2 months using an identical testing protocol with biphasic waveforms.
• Patients were followed for 4 to 15 months, with DFT assessed at implant, 2 months, and 6 months.

Main Results:

• The mean DFT showed a significant increase from 9.8 J at implant to 13.2 J at 2 months and 12.4 J at 6 months (p = 0.01).
• No significant changes were observed in clinical status, cardiac size, lead position, or impedance between implant and 2 months.
• The increase in DFT was consistent across patients, irrespective of the shocking electrode configuration (lead-only vs. subcutaneous patch).

Conclusions:

• The chronic increase in defibrillation threshold observed in this non-thoracotomy ICD system is not dependent on the waveform type (monophasic vs. biphasic).
• The findings suggest that the phenomenon is an inherent characteristic of non-thoracotomy electrodes rather than epicardial electrodes.
• This highlights the importance of considering lead system design in long-term ICD performance and efficacy.