Effects of the atrial pacing site on rate-dependent av nodal
function in the rabbit heart.
Amellal, Farid, and Jacques Billette.
Department of Physiology, Faculty of Medicine, University of
Montreal, Montreal, Canada
APStracts 2:0139H, 1995.
The functional origin of the changes in AV nodal function with the
atrial pacing site was studied in isolated rabbit heart preparations.
The rate-dependent AV nodal properties of recovery, facilitation and
fatigue were characterized with premature stimulation protocols
repeated for each of three atrial pacing sites (upper atrium, low
crista terminalis and low interatrial septum). The effects of the
atrial pacing site, reference site from which beginning of nodal
activation is measured (low crista and low septum), and stimulation
protocol on nodal conduction and refractory parameters were assessed
with multifactorial analyses of variance. The changes in nodal
parameters with the stimulation protocol did not differ significantly
with the pacing site, indicating that the rate-dependent nodal
properties are not affected by the atrial origin of the impulse. Only
the baseline value of nodal parameters varied with the atrial pacing
and reference site. However, the comparison of data obtained while
the low crista was the pacing and reference site to those obtained
while the low septum was the pacing and reference site yield no
statistically significant differences, thus indicating that changes
in perinodal activation were largely responsible for the observed
changes in baseline. Upper atrial and low crista pacing yielded very
similar data. Conclusions: 1) The atrial pacing site affects
perinodal activation but not rate-dependent nodal function. 2) The
two inputs are equally effective in activating the AV node. 3) Input
summation is a minor factor in rate-dependent nodal function.
Received 23 December 1994; accepted in final form 28 March 1995.
APS Manuscript Number H1132-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 19 April 1995.