Long pacing pulses reduce phrenic nerve stimulation in left ventricular pacing
Søren Hjortshøj1, Finn Heath1, Morten Haugland2
1Department of Cardiology, Aalborg University Hospital.
Insights
Longer electrical pulse durations in cardiac resynchronization therapy (CRT) can reduce the risk of phrenic nerve stimulation. This study found that longer pulses favor left ventricular pacing over phrenic nerve activation.
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.
Introduction:
Phrenic nerve stimulation is a major obstacle in cardiac resynchronization therapy (CRT). Activation characteristics of the heart and phrenic nerve are different with higher chronaxie for the heart. Therefore, longer pulse durations could be beneficial in preventing phrenic nerve stimulation during CRT due to a decreased threshold for the heart compared with the phrenic nerve. We investigated if long pulse durations decreased left ventricular (LV) thresholds relatively to phrenic nerve thresholds in humans.
Methods And Results:
Eleven patients, with indication for CRT and phrenic nerve stimulation at the intended pacing site, underwent determination of thresholds for the heart and phrenic nerve at different pulse durations (0.3-2.9 milliseconds). The resulting strength duration curves were analyzed by determining chronaxie and rheobase. Comparisons for those parameters were made between the heart and phrenic nerve, and between the models of Weiss and Lapicque as well. In 9 of 11 cases, the thresholds decreased faster for the LV than for the phrenic nerve with increasing pulse duration. In 3 cases, the thresholds changed from unfavorable for LV stimulation to more than a factor 2 in favor of the LV. The greatest change occurred for pulse durations up to 1.5 milliseconds. The chronaxie of the heart was significantly higher than the chronaxie of the phrenic nerve (0.47 milliseconds vs. 0.22 milliseconds [P = 0.029, Lapicque] and 0.79 milliseconds vs. 0.27 milliseconds [P = 0.033, Weiss]).
Conclusion:
Long pulse durations lead to a decreased threshold of the heart relatively to the phrenic nerve and may prevent stimulation of the phrenic nerve in a clinical setting.
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