AJP - Heart and Circulatory Physiology, Vol 249, Issue 1 133-H140, Copyright © 1985 by American Physiological Society
Differential responses accompanying sequential stimulation and ablation of vagal branches to dog heart
W. C. Randall, J. L. Ardell and D. M. Becker
Electrical excitation of small thoracic vagal branches elicited highly
localized responses in the canine heart. Specific pathways to the
sinoatrial nodal (SAN) regions were identified from negative chronotropic
responses to stimulation (20 Hz, 5.0 ms, 3.0-5.0 V) of these branches.
Pathways to the atrioventricular nodal (AVN) region were determined from
changes in A-H interval (His bundle electrogram) and incidence of heart
block as vagal branches were stimulated during concurrent atrial pacing. A
few small branches influenced a single cardiac function (atrial rate,
contractile force, or AV conduction). More commonly, activation of such
branches elicited simultaneous chronotropic and dromotropic effects.
However, many branches failed to elicit any detectable cardiac change. The
major outflow from the left vagus to SAN and AVN regions is by way of
cardiac branches from the recurrent laryngeal nerve at its reflection
around the aorta. Activation of the left recurrent nerve reduced atrial
rate by 43% and doubled A-H interval 84 to 167 ms. The right thoracic vagus
or its branches induced A-H prolongation from 78 to 131 ms. H-V intervals
remained constant at a mean of 35 ms. Outflows from the right thoracic
vagus to SAN and/or AVN regions originated just below the middle cervical
ganglion and at all levels down to the azygos vein.
