Mechanisms of conduction time hysteresis in rabbit atrioventricular
node.
Billette, Jacques, Jie Zhao, and Alvin Shrier.
Department of Physiology, Faculty of Medicine, University of
Montreal, and Department of Physiology, Faculty of Medicine, McGill
University, Montreal, Canada
APStracts 2:0167H, 1995.
The functional origin of AV nodal hysteresis was studied in isolated
rabbit heart preparations. This hysteresis is characterized by
asymmetric changes in nodal conduction time (NCT) occurring for
symmetric changes in cycle length. The respective contribution of the
nodal properties of recovery, facilitation and fatigue to the beat to
beat changes in NCT observed during paired symmetric ramps of
decreasing and increasing cycle length was determined with
specifically design stimulation protocols. Nodal hysteresis was found
to be entirely accounted for by variations in the contribution of
nodal recovery and fatigue properties observed at corresponding cycle
lengths. The study establishes how this contribution varies on a beat
to beat basis as a result of cycle length history. This holds true
for the numerous changes in hysteresis observed in response to
changes in the sequence and slope of the ramps. Facilitation clearly
affected NCT during these responses but did not contribute to the
hysteresis. Moreover, the study demonstrates that there is no
inherent change in the characteristics of nodal function with the
direction of the ramp that could account for the hysteresis. Thus,
nodal hysteresis arises from nodal functional properties of recovery
and fatigue but does not constitute a distinct independent intrinsic
property of the node.
Received 9 May 1994; accepted in final form 3 April 1995.
APS Manuscript Number H403-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 2 May 1995.