Abstract 16255: Left Cervical Vagal Nerve Stimulation Suppresses Cardiac Sympathetic Tone

Abstract

Background: In ambulatory dogs, the left cervical vagal nerve stimulation (VNS) reduces stellate ganglion nerve activity (SGNA) and heart rate, while upper thoracic skin sympathetic nerve activity (SKNA) has been shown to be a surrogate of SGNA to measure sympathetic tone. Objective: To test the hypothesis that VNS suppresses SKNA in human. Methods: We used conventional electrocardiogram (ECG) patches to continuously record SKNA in 12 patients who were admitted for video electroencephalographic monitoring. The ECG patches were placed under the right subclavian and left subclavian areas to form Lead I. The signals were band pass filtered between 200 to 1000 Hz to reveal SKNA. All antiepileptic medications were withdrawn. No patients had known organic heart diseases. No seizures occurred during the recording period. Nerve activity was quantified by integrating (iSKNA) the absolute value of the filtered signal over a 1 min window at intervals of 2 min, 20 min, and 40 min past each hour between 6 AM and 1 PM. Heart rate was determined by calculating the R-R intervals. Results: Six patients (2 men, age 40±5 years ) received chronic left cervical VNS (VNS group) and 6 (1 man, age 44±7 years) had no VNS pacing (control group). The admission diagnoses were generalized seizure (N=1) and partial seizure (N=5) in VNS group; generalized seizure (N=2) and partial seizure (N=4) in control group. The VNS pacing was continuous with an ON-time of 30 s and OFF-time of 158±72 s. The output was 1.92±0.42 mA with a frequency of 24.17±2.01 Hz. Fast Fourier Transform of the signals showed only physiologic activity between 200-1000 Hz. The iSKNA during VNS OFF-time was 13.77 mV-s [95% confidence interval, CI, 11.09 to 16.45], which was significantly lower than 20.75 mV-s [95% CI, 16.34 to 25.16, p=0.006] of the control Group. The heart rate was 67 bpm [95% CI, 60 to 74] in VNS group, significantly lower than 73 bpm [95% CI, 63 to 84] in control group. Conclusion: Patients with left cervical VNS had lower heart rate and iSKNA than patients without VNS. These findings are consistent with those observed in ambulatory canines, and suggest that chronic intermittent VNS can suppress cardiac sympathetic tone in human.