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.

Background Stellate ganglion nerve activity (SGNA) is important in cardiac arrhythmogenesis. However, direct recording of SGNA requires access to the thoracic cavity. Skin of upper thorax is innervated by sympathetic nerve fibers originating from the stellate ganglia (SG) and is easily accessible. Objective To test the hypothesis that thoracic skin nerve activity (SKNA) can be used to estimate SGNA. Methods We recorded SGNA and SKNAs using surface electrocardiogram leads in 5 anesthetized and 4 ambulatory dogs. Apamin injected into the right SG abruptly increased both right SGNA and SKNA in 5 anesthetized dogs. We integrated nerve activities and averaged heart rate in each one-min window over 10 min. We implanted a radiotransmitter to record left SGNA in 4 ambulatory dogs, including two normal dogs, one dog with myocardial infarction and one dog with intermittent rapid atrial pacing. After 2 weeks of recovery, we simultaneously recorded the SKNA and left SGNA continuously for 30 min when the dogs were ambulatory. Results There was a positive correlation (average r=0.877, 95% confidence interval (CI) 0.732 to 1.000, p<0.05 for each dog) between integrated SKNA (iSKNA) and SGNA (iSGNA) and between iSKNA and heart rate (average r=0.837, 95% CI 0.752 to 0.923, p<0.05). Similar to that found in the anesthetized dogs, there was a positive correlation (average r=0.746, 95% CI 0.527 to 0.964, p<0.05) between iSKNA and iSGNA and between iSKNA and heart rate (average r=0.706, 95% CI 0.484 to 0.927, p<0.05). Conclusions SKNAs can be used to estimate SGNA in dogs.

Background Renal sympathetic denervation (RD) is a promising method of neuromodulation for the management of cardiac arrhythmia. Objective We tested the hypothesis that RD is antiarrhythmic in ambulatory dogs because it reduces the stellate ganglion nerve activity (SGNA) by remodeling the stellate ganglion (SG) and brain stem. Methods We implanted a radiotransmitter to record SGNA and electrocardiogram in 9 ambulatory dogs for 2 weeks, followed by a 2nd surgery for RD and 2 months SGNA recording. Cell death was probed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Results Integrated SGNA at baseline, 1 and 2 months after RD were 14.0±4.0, 9.3±2.8 and 9.6±2.0 μV, respectively (p=0.042). The SG from RD but not normal control (N=5) dogs showed confluent damage. An average of 41±10% and 40±16% of ganglion cells in the left and right SG, respectively, were TUNEL-positive in RD dogs compared with 0% in controls dogs (p= 0.005 for both). Left and right SG from RD dogs had more tyrosine hydroxylase-negative ganglion cells than left SG of control dogs (p= 0.028 and 0.047 respectively). Extensive TUNEL positive neurons and glial cells were also noted in the medulla, associated with strongly positive glial fibrillary acidic protein staining. The distribution was heterogeneous, with more cell death in the medial than lateral aspects of the medulla. Conclusion Bilateral RD caused significant central and peripheral sympathetic nerve remodeling and reduced SGNA in ambulatory dogs. These findings may in part explain the antiarrhythmic effects of RD.