Abstract 12365: Are there Sympathetic Nerve Fibers in Human Cervical and Thoracic Vagus Nerves?: Implications for Therapeutic Vagal Stimulation
Introduction: Cervical vagal nerve stimulation has been used to treat resistant partial-onset seizures and is being evaluation in clinical trials for treatment of heart failure and cardiac arrhythmias. While improvement of symptoms has been reported, there have also been serious adverse events, including cardiac arrhythmias and death. Immunohistochemical studies for tyrosine hydroxylase (TH) have shown that canine cervical vagus nerves (VN) consistently contain a component of sympathetic fibers. Only one study has shown TH positive fibers in human VN. In this study we quantified the sympathetic components of human VN that could contribute to both the therapeutic and serious adverse events reported with cervical VN stimulation therapy.
Methods: We harvested cervical and thoracic VN from seven human autopsies; 4 males, 3 females (mean age = 67 yr, range = 45-99 yr). The tissues were processed routinely, paraffin embedded, cut into 5-μm thick sections, and immunostained for TH to identify adrenergic nerve fibers. Glass slides were scanned at 20x with an Aperio XT scanner (Aperio Technologies, Vista, CA). Morphometry was used to calculate the cross-sectional total nerve and TH positive areas within the VNs.
Results: A total of 28 individual nerves were examined from human right/left and cervical/thoracic VN, mean total cross area = 1.34 mm2; (median = 1.29, range = 0.77-2.73). All VNs contain TH-positive (sympathetic) nerves. Location of sympathetic fibers was variable, and occupied a mean 34.7% of VN cross-sectional area (median = 39.9, range 0.67-75.1).
Conclusion: Sympathetic nerve fibers are invariably present in human cervical and thoracic vagus nerves and comprise an average of 35% of the total nerve tissue. Vagus nerve stimulation cannot be purely parasympathetic. The contribution of sympathetic stimulation to both therapeutic and adverse events after cervical vagus nerve stimulation therapy remains to be determined.
- © 2013 by American Heart Association, Inc.