Estimating Sympathetic Tone by Recording Subcutaneous Nerve Activity in Ambulatory Dogs

Abstract

Introduction We tested the hypothesis that subcutaneous nerve activity (SCNA) of the thorax correlates with the stellate ganglion nerve activity (SGNA) and can be used to estimate the sympathetic tone. Methods and Results We implanted radiotransmitters in 11 ambulatory dogs to record left SGNA, left thoracic vagal nerve activity (VNA) and left thoracic SCNA, including 3 with simultaneous video monitoring and nerve recording. Two additional dogs were studied under general anesthesia with apamin injected into the right stellate ganglion while the right SGNA and the right SCNA were recorded. There was a significant positive correlation between integrated SGNA (iSGNA) and integrated SCNA (iSCNA) in the first 7 ambulatory dogs, with correlation coefficient of 0.70 (95% confidence interval, CI, 0.61 to 0.84, p < 0.05 for each dog). Tachycardia episodes (heart rate exceeding 150 bpm for ≥3 s), were invariably preceded by SGNA and SCNA. There was circadian variation of both SCNA and SGNA. Crosstalk was ruled out because SGNA, VNA and SCNA bursts had different timing and activation patterns. In an 8th dog, closely spaced bipolar subcutaneous electrodes also recorded SCNA, but with reduced signal to noise ratio. Video monitoring in additional 3 dogs showed that movement was not a cause of high frequency SCNA. The right SGNA correlated strongly with right SCNA and heart rate in 2 anesthetized dogs after apamin injection into the right stellate ganglion. Conclusions SCNA recorded by bipolar subcutaneous electrodes correlates with the SGNA and can be used to estimate the sympathetic tone.

Subcutaneous nerve activity and spontaneous ventricular arrhythmias in ambulatory dogs

“…Similar to a prior report in normal canines, 8 all seven dogs demonstrated subcutaneous nerve discharges with similar morphology to the signals recorded from the left stellate ganglion. In addition, SCNA morphology was similar to filtered skin and muscle sympathetic nerve activity obtained in microneurography studies.…”

“…In the present study, the presence of SCNA was demonstrated in all seven dogs using widely spaced bipolar electrodes placed in the upper trunk. Similar to that in normal dogs, 8 SCNA in these diseased dogs had similar morphology, onset and duration compared to SGNA, but the recordings were sufficiently different to eliminate significant cross talk between the channels. In addition, SCNA signals were similar to filtered human microneurography signals obtained directly from a peripheral nerve.…”

“…The study by Robinson et al demonstrates that apamin injection in the stellate ganglion results in increased signal in the subcutaneous nerves. 8 These findings suggest that SCNA represents peripheral output of increased sympathetic outflow. However, additional studies utilizing central pharmacological blockade with drugs such as clonidine or stellate ganglion ablation and measuring SGNA and SCNA should be undertaken to further elucidate the specific interplay between SCNA and SGNA.…”

“…We 8 have recently reported that in ambulatory and anesthetized normal dogs, SCNA recorded by bipolar subcutaneous electrodes correlates with the SGNA and can be used to estimate the sympathetic tone. In the present study, the presence of SCNA was demonstrated in all seven dogs using widely spaced bipolar electrodes placed in the upper trunk.…”

“…We have recently shown that SCNA correlates well with SGNA and heart rate in normal ambulatory dogs. 8 It is not clear, however, if SCNA can be used to predict the onset of ventricular arrhythmias and SCD in diseased animals. The aim of the present study is to employ an established canine model of SCD and investigate the relationship between SCNA, SGNA, ventricular arrhythmias and SCD.…”