Memory and complex dynamics in cardiac purkinje fibers.
Gilmour, Robert F., Jr. Niels F. Otani and Mari Watanabe.
Department of Physiology1 and Cornell Theory Center2, Cornell
University, Ithaca, New York
APStracts 3:0520H, 1996.
The contribution of cumulative changes in action potential duration
(memory) to complex cellular electrophysiological behavior was
investigated in canine cardiac Purkinje fibers. Complex behavior
induced during constant pacing was caused by reciprocal interactions
between the time to full repolarization (TFR), where TFR = response
duration + latency, and the diastolic interval (DI). The relationship
between TFR and the preceding DI during complex behavior differed
from that obtained using a standard restitution protocol. In
particular, higher order periodicities and chaos were produced in
fibers in which the restitution curve lacked the prerequisites for
such behavior. To investigate whether shifts in the restitution curve
might be expected during rapid pacing, the relationship between TFR
of a test response (TFRn+1) and the immediately preceding response
(TFRn) was determined. For any fixed DIn, reduction of TFRn from 240
to 130 msec was accompanied by a corresponding reduction of TFRn+1,
whereas as TFRn was reduced further to 120 msec, TFRn+1 increased.
Because of the dependence of TFRn+1 on TFRn (memory) and on the
preceding DIn (restitution), the slope of the low dimensional
relationship between TFRn+1 and DIn at a constant pacing cycle length
depended on the slopes of both the restitution and memory functions.
These results suggest that rapid accumulation and dissipation of
memory may contribute importantly to complex electrical behavior in
cardiac tissue.
Received 24 January 1996; accepted in final form 28 October 1996.
APS Manuscript Number H68-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996