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1 Institute of Biomedical and Life Sciences, Glasgow University, Glasgow G12 8QQ, United Kingdom; 2 Center for Interdisciplinary and Complex Systems, Northeastern University, Boston, Massachusetts 02115; and 3 Medizinische Klinik der Universität Würzburg, 97080 Würzburg, Germany
Decreasing the slope
of the dynamic, but not conventional, restitution curves is
antifibrillatory. Cardiac memory/accommodation underlies the
difference. We measured diastolic interval (DI) and action potential
duration (APD) in epicardial, endocardial, and Purkinje tissue from
eight dogs. Consecutive 100-stimulus trains were given to study
transitions between basic cycle lengths (BCL) ranging from 400 to 1,300 ms. (DI,APD) pairs aligned immediately on the line DI + APD = BCL (64/67) or oscillated (3/67). The shifting effect of up to 10 extrastimuli on restitution curves was also measured. These curves were
fit with the equation APD =
+
exp(
DI/
), where
is asymptote,
is drop, and
is time constant. Linear
regression of the parameters against the number of extrastimuli showed
that premature and postmature stimuli decreased and increased
and
and increased and decreased
, respectively. Analysis of a
mathematical model treating memory as an exponentially decreasing shift
of restitution curves shows that oscillatory DI,APD is expected with
large
BCL, steep restitution slope, or increased cardiac accommodation. The model explains phase shifts and suggests a common
mechanism for Purkinje and myocardial electrical alternans.
arrhythmias; dynamic restitution; short-term memory; modeling
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