AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 2 235-R243, Copyright © 1983 by American Physiological Society
Effect of cervical vagal stimulation on chicken heart rate and atrioventricular conduction
J. M. Goldberg, M. H. Johnson and K. D. Whitelaw
The effects of supramaximal stimulation of the right and left cervical vagi
on heart rate, pacemaker localization, and atrioventricular (AV) conduction
were investigated in 15 anesthetized open-chest chickens before and after
atropine sulfate. Epicardial bipolar electrograms were recorded from
selected atrial sites and right ventricle. A back lead electrocardiogram
was also recorded. The effect of stimulation on atrioventricular conduction
was evaluated during pacing from one of the right atrial recording sites.
Supramaximal stimulation of either cervical vagus produced bradycardia but
not cardiac arrest. Heart rate was reduced from an average spontaneous rate
of 282 +/- 13 (SE)/min to 161 +/- 13/min with stimulation of the right and
left cervical vagus. Pacemaker shifts occurred in over 50% of the vagal
stimulations. The most frequent shift occurred to the lower AV node or
ventricles. Pacemaker shifts to the AV junctional region producing almost
simultaneous activation of the atria and ventricles were not observed.
Vagal stimulation during atrial pacing produced minimal prolongation in AV
conduction time [right vagus, 13 +/- 3 (SE) ms; left vagus, 8 +/- 2 ms].
Second and third degree heart blocks were not observed during pacing. Vagal
stimulation after atropine indicates that the cervical vagi do not contain
sympathetic fibers going to pacemaker or AV conduction tissues.
