Abstract 17552: Beat to Beat Control of Sinus Rate by Sympathetic Nerve Activity in Normal Anesthetized Dogs

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Introduction: The coupling between local nerve activity and electrical activation at the sinoatrial node (SAN) remains unclear.

Hypothesis: We hypothesized that there is beat-to-beat coupling between nerve activity and electrical activity at the SAN, and that right stellate ganglion (RSG) stimulation can increase the local nerve activity, accelerate sinus rate, and change the earliest activation site (EAS).

Methods: We placed a plaque with 896 electrodes (32 rows and 28 columns, 1mm interelectrode distance) on the epicardial surface of the right atrium (RA) in 5 open-chest anesthetized dogs including 3 males and 2 females. The electrical signals were recorded by the plaque with 896 electrodes connected to Unemap computerized mapping system sampled at 4 kHz. The signals were bandpass filtered between 500-1000 Hz to display nerve activity and between 0.5-150 Hz to display electrical activity.

Results: Local nerve activity was absent during isoflurane or alpha chloralose anesthesia. However, RSG stimulation at 20-Hz or RSG apamin (100 nmol/L, 1 ml) injection induced local nerve activity (arrows in Figure) that preceded each atrial electrogram, with an average nerve activity amplitude of 3.57±0.80 μV and 3.93±0.59 μV, respectively. Heart rate accelerated from 106±5 bpm at baseline to 126±7 bpm after RSG stimulation (p<0.05), and to 137±5 bpm after apamin (p<0.05). The sinus node recovery time (SNRT) at a 300 ms pacing cycle length shortened from 564±42 ms at baseline to 485±44 ms after RSG stimulation (p<0.05), and to 457±41ms after apamin (p<0.05). In 3 dogs, RSG resection eliminated the local nerve activity. After cutting the RSG, heart rate decreased and SNRT prolonged to 676±106 ms. The EAS of the SAN moved cranially by 5.1±2.5 mm when pacing RSG and by 5.4±1.0 mm after injecting apamin. After cutting RSG, EAS of the SAN moved caudally.

Conclusions: RSG stimulation activates local sympathetic nerves at SAN, resulting in beat-to-beat control of the sinus rate.

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