Long pacing pulses reduce phrenic nerve stimulation in left ventricular pacing

Area of Science:

• Cardiology
• Biomedical Engineering
• Electrophysiology

Background:

• Phrenic nerve stimulation is a significant challenge in cardiac resynchronization therapy (CRT).
• Differences in activation characteristics between the heart and phrenic nerve, specifically chronaxie, influence stimulation thresholds.

Purpose of the Study:

• To investigate whether extended pulse durations decrease left ventricular (LV) stimulation thresholds relative to phrenic nerve thresholds in humans.
• To determine the optimal pulse durations for selective LV pacing during CRT.

Main Methods:

• Eleven patients with CRT indication and phrenic nerve stimulation underwent threshold determination at varying pulse durations (0.3-2.9 ms).
• Strength-duration curves were analyzed to compare chronaxie and rheobase between the heart and phrenic nerve using Weiss and Lapicque models.

Main Results:

• In 9 out of 11 patients, LV thresholds decreased more rapidly than phrenic nerve thresholds with increasing pulse duration.
• In 3 patients, thresholds shifted to favor LV stimulation by over a factor of 2.
• The most significant changes were observed for pulse durations up to 1.5 ms.
• Heart chronaxie was significantly higher than phrenic nerve chronaxie (0.47 ms vs. 0.22 ms, P=0.029 [Lapicque]; 0.79 ms vs. 0.27 ms, P=0.033 [Weiss]).

Conclusions:

• Prolonged pulse durations reduce the stimulation threshold of the heart relative to the phrenic nerve.
• This approach holds potential for preventing phrenic nerve stimulation in clinical CRT settings.