Effect of Vagus Nerve Stimulation on Heart Rate Variability
Abstract number :
1.132
Submission category :
Year :
2001
Submission ID :
3055
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
G.A. Charlton, MD, Neurology, University of New Mexico, Albuquerque, NM; E. Cruz, School of Medicine, University of New Mexico, Albuquerque, NM; E. Ergene, MD, Neurology, University of New Mexico, Albuquerque, NM
RATIONALE: The vagus nerve is a mixed nerve which carries somatic and visceral afferents and efferents, providing an important contribution to heart rate via parasympathetic autonomic input. This input is asymmetric, with the sinoatrial node and atrioventricular node receiving innervation from the right and left vagus nerve, respectively. Animal studies have shown that stimulation of the right vagus nerve produces a more pronounced bradycardic effect than stimulation of the left vagus. This is a key point which is exploited when implanting the vagus nerve stimulator (VNS) for treatment of medically refractory epilepsy, exclusively utilizing the left vagus nerve to prevent unwanted bradyarrhythmias.
METHODS: We evaluated heart rate variability in patients with implanted vagus nerve stimulators, both during stimulation as well as [dsquote]off[dsquote] time, using medically treated epilepsy patients as age-matched controls. Heart rate variability was examined using the standard deviation of R-R intervals (SD of RR) in 30 beat blocks during vagus nerve stimulation ([dsquote]stimulator on[dsquote]) as well 1 minute pre- and post-stimulation ([dsquote]stimulator off[dsquote]); 2 cycles for each patient were recorded. Six 30 beat blocks at random time intervals were recorded for each of the controls.
RESULTS: There was significantly less variability in duration of the R-R interval, both with the stimulator on and off, in VNS patients when compared to controls (Mean of SD of RR interval with stimulator on = 33.2 [plusminus] 19.2 ms; mean of SD of RR interval with stimulator off = 39.0 [plusminus] 20.0 ms; mean of SD of RR in controls = 54.6 [plusminus] 32.0 ms. Using Student t-test, comparing [dsquote]stimulator on[dsquote] vs. controls p [lt] 0.01; comparing [dsquote]stimulator off[dsquote] vs. controls p [lt] 0.02). There was no statistically significant difference in heart rate variability within the patient group comparing stimulator on vs. off.
CONCLUSIONS: While long term intermittent stimulation of the left vagus nerve is not known to produce pronounced bradycardia, our results indicate that it does cause a decrease in heart rate variability. This appears to be a long-lasting or chronic effect as evidenced by a decreased variability in duration of the R-R interval even while the stimulator is off in comparison to controls. The clinical significance of this decreased heart rate variability is currently not known and warrants further study.
Support: This study was supported by NIH NCRR GCRC Grant 5 MO1 RRO997.