Characterization of atrioventricular nodal response to electrical left vagal stimulation

The dynamic effect of left vagal stimulation on atrioventricular conduction was studied in six isofluorane-anesthetized dogs ranging in weight from 22 to 29 kg. The cervical vagus nerve trunks were left intact and no beta-adr energic blockade tvas produced so that any influences of the sympathetic ne rvous system and autonomic reflex activity could be observed. Atrial pacing was used to control the heart rate while single, short trains of left vaga l stimulation were delivered and timed to occur at different instants durin g the cardiac cycle. The magnitude of the A-V delay depended on the instant of delivery of the train of vagal stimuli during the cardiac cycle. Vagal effect curves were constructed and fit to a mathematical equation which des cribes the pharmokinetic behavior of a bolus injection of a drug whose onse t time is of the same order as its half-life. The three parameters of this equation have physiologic significance: and are related to nerve propagatio n time and synaptic delay, acetylcholine concentration rise, and the acetyl cholineesterase mechanism. The maximum A-V delay occurred when the short tr ain of left vagal stimuli was applied 200-300 ms after the atrial pacing st imulus and the total effect was virtually over by 800-1000 ms. (C) 1999 Bio medical Engineering Society. [S0090-6964(99)00806-1].