Cardiovascular Function during Vagus Nerve Stimulation: A Study of Exercise Stress Test and Echocardiogram
Abstract number :
1.136
Submission category :
Year :
2001
Submission ID :
2747
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
A. Hinderliter, MD, Medicine, University of North Carolina, Chapel Hill, NC; B.V. Vaughn, MD, Neurology, UNC, Chapel Hill, NC; S. Quint, PhD, Biomedical Engineering, UNC, Chapel Hill, NC; E. Bernard, MD, Surgery, UNC, Chapel Hill, NC; R. Greenwood, MD, Ne
RATIONALE: Vagus nerve stimulation is a growing therapy for intractable epilepsy. The left vagus nerve has a small but significant innervation to the cardiac system. Recent cases of asystole during stimulator implantation have raised questions regarding the effect of left vagus nerve stimulation on the heart.
METHODS: As a component of a battery of cardiovascular tests, we performed exercise stress tests and echocardiograms upon 13 subjects with intractable epilepsy, who had three months of intermittent left vagus nerve stimulation. The stimulators were turned off and the subjects were exercised to 70 and 85 % of the maximal heart rate. The stimulator was then activated for 2.5 minutes at each level of exercise (maximal tolerated current, signal frequency-30 Hz, pulse width-500 microseconds). Heart rate, blood pressure and electrocardiogram features were monitored throughout the exercise period. Subsequently at rest, Doppler echocardiography was also performed with the stimulator off and on. Stroke volume and cardiac output were measured. Parameters with and without stimulation were compared using a paired t test (p[lt]0.05).
RESULTS: Fifteen subjects were enrolled in the study and 13 subjects had interpretable data. We found a small but statistically significant increase in heart rate during the period of stimulation at both levels of exercise (2.15 bpm for 70% (p=0.009) and 1.9 bpm for 85% (p=0.047)). We found no significant change in cardiac rhythm or blood pressure during stimulation when subjects were exercising at workloads producing 70 or 85 % of their maximal heart rate. We found that subjects had a mild resting tachycardia (mean 96 bpm) prior to the exercise. Analysis of the echocardiogram showed no change in heart rate, stroke volume or cardiac output during stimulation at rest.
CONCLUSIONS: In our series, we found no hemodynamically significant changes in cardiac function during rest and exercise when challenged by vagus nerve stimulation. We found a mild increase in heart rate associated with stimulation during continued exercise, but this increase is probably an adaptation to continued exercise. These findings suggest that left vagus nerve stimulation has minimal effect on the cardiovascular system during rest and exercise.
Support: This study was funded by Cyberonics.
Disclosure: Grant - Cyberonics. Honoraria - Cyberonics.