AJP - Heart and Circulatory Physiology, Vol 253, Issue 5 1059-H1068, Copyright © 1987 by American Physiological Society
Differential vagal effects on antegrade vs. retrograde atrioventricular conduction
T. Mitsuoka, T. Mazgalev, L. S. Dreifus and E. L. Michelson
Lankenau Medical Research Center, Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pennsylvania 19151.
The influence of postganglionic vagal stimulation (PGVS) on antegrade and
retrograde atrioventricular nodal conduction was studied in 17 isolated
rabbit heart tissue preparations by pacing at the crista terminalis or His
bundle, respectively. The effect of short bursts of PGVS on prolongation of
atrioventricular conduction was phase dependent with respect to the cardiac
cycle. This phasic dependency was more pronounced during antegrade
atrioventricular conduction. Although the control retrograde
atrioventricular conduction time was longer than the antegrade (P less than
0.05) at or near the time in the cycle during which vagal stimulation
caused maximal prolongation of conduction time (optimal phase),
PGVS-induced maximal prolongation of the antegrade atrioventricular
conduction time was significantly greater than that of the retrograde (P
less than 0.02). Moreover, when PGVS was introduced at a fixed phase in the
cycle, but with increasing amplitude, antegrade atrioventricular conduction
time was progressively prolonged, and block was observed first in the
antegrade direction, whereas retrograde atrioventricular conduction
continued. Microelectrode recordings during these experiments showed
consistently that PGVS-induced hyperpolarization in the N region of the
atrioventricular node was greater during antegrade atrioventricular
conduction. This suggests that vagal effects depended not only on the
intensity and phase of stimulation, but also on electronic influences which
apparently are different during antegrade and retrograde conduction.
