Abstract 15543: Baseline Sympathetic Nerve Activity Within the Thoracic Vagus Nerve
Introduction: Immunohistochemical studies from our laboratory showed that the both cervical and thoracic vagus nerves (VN) contain a small component of sympathetic nerves. Furthermore, the cervical VN contains abundant sympathetic ganglion cells, indicating that the cervical VN may independently generate sympathetic tone. We hypothesize that in ambulatory dogs, sympathetic nerve activity is an important component of the vagal nerve activity (VNA).
Methods: We performed simultaneous recording of left stellate ganglion nerve activity (SGNA), left thoracic VN activity (VNA) and subcutaneous ECG in 9 ambulatory dogs for 24 hour duration. Data were manually analyzed to detect recordings in which VNA activates alone, without simultaneous SGNA.
Results: The sympathetic component of the thoracic VN is active in 3 of the 9 dogs studied. Figure shows an example in which thoracic VNA was active while the SGNA was quiescent. The VNA activity showed a burst-termination pattern typical for peripheral nerves. (Arrows indicate the bursts). There was immediate heart rate acceleration during the VNA bursts, indicating that these nerve activities came from sympathetic component within the thoracic VN. There were 33.3 ± 28.5 episodes of lone VNA activations in 3 dogs, all showed similar burst-termination pattern. The heart rate was increased from 54.9 ± 24.2 bpm immediately prior to the VNA bursts to 132.7 ± 26.6 bpm (p < 0.001) during the VNA bursts. An average episode of the burst-termination pattern lasted 187.8 ± 289.0 minutes in these 3 dogs.
Conclusion: The sympathetic nerves within the thoracic VN may activate alone and accelerate the heart rate. These findings suggest that the proarrhythmic effects of vagal nerve stimulation in experimental models may be due to simultaneous sympathetic and parasympathetic activation, rather than parasympathetic activation alone.
- © 2012 by American Heart Association, Inc.