Increased subcutaneous nerve activity is strongly associated with the initiation of atrial tachyarrhythmias in ambulatory canines.

BACKGROUND: Increased stellate ganglion nerve activity (SGNA) directly precedes the onset of spontaneous atrial tachyarrhythmias (AT) in ambulatory dogs. However, it is difficult to use SGNA for risk stratification and arrhythmia prediction because access to the stellate ganglion requires open chest surgery. Because subcutaneous sympathetic nerve fibers originate from ipsilateral stellate ganglion, we hypothesize that subcutaneous nerve activity (SCNA) can be used as a surrogate of SGNA to predict the immediate onset of AT in ambulatory dogs.

METHODS: We continuously recorded SCNA and ECG in 4 ambulatory dogs using an implanted radiotransmitter with electrodes in the subcutaneous space of the left chest. The dogs were atrially paced at 600 bpm for 6 days. The dogs were also treated with digoxin (0.01 mg/kg daily) and diltiazem CD (6 mg/kg daily) to reduce ventricular rates. ECG, SCNA, and SGNA were reviewed for a 24-hour period before and after 6 days of pacing. SCNA and SGNA were also integrated (iSCNA and iSGNA) at 1-minute intervals for 10 minutes of each hour of the 24 hours reviewed. Episodes of AT were identified as a heart rate >150 bpm for at least 5 seconds. SCNA and SGNA were integrated over the 5 seconds preceding each episode of AT (iSCNAAT and iSGNAAT). Also, SCNA and SGNA were integrated for 5 seconds during random episodes of normal sinus rhythm (iSCNANSR and iSGNANSR, respectively).

RESULTS: There were 14 ± 20 episodes/dog/day of spontaneous AT at baseline and 20 ± 25 episodes/dog/day after rapid atrial pacing (P <.05). We analyzed 118 episodes (41 ± 42 per dog) of AT, including 58 episodes of atrial fibrillation and 60 of regular atrial tachycardia, with an average duration of 12 ± 6 seconds/episode. AT was invariably preceded by SCNA activation within 5 seconds before onset. iSCNAAT was significantly greater than iSCNANSR (31.9 ± 18.7 mv-s vs 6.9 ± 4.45 mv-s, P <.005).

CONCLUSIONS: Spontaneous AT in ambulatory dogs was invariably preceded by an increased SCNA. These findings suggest that SCNA is an effective biomarker for predicting the onset of AT in this canine model.