AJP - Heart and Circulatory Physiology, Vol 256, Issue 4 956-H961, Copyright © 1989 by American Physiological Society
Monophasic action potential recordings in response to graded hyperkalemia in dogs
P. M. Sutton, P. Taggart, D. W. Spear, H. F. Drake, R. H. Swanton and R. W. Emanuel
Department of Physiology, University College and Middlesex Hospital School of Medicine, London, United Kingdom.
Recent interest in sudden cardiac death during exercise in normal healthy
people has highlighted the possible role of swings of extracellular
potassium in arrhythmogenesis in conditions other than ischemia. Regional
differences in action potential duration and conduction may be important.
We have recorded monophasic action potentials (MAPs) from the endocardium
and epicardium in nine open-chest dogs during graded intravenous infusion
of potassium up to a plasma level of 9 mM. The animals were anesthetized
with alpha-chloralose and urethan. Continuous, online arterial potassium
monitoring was employed. MAP duration showed a biphasic response with
initial shortening up to 7 mM, which tended to be more obvious on the
epicardium. Regional activation time was measured as the difference between
the onset of depolarization of the endocardial and epicardial MAP. Regional
activation time also showed a biphasic response with initial shortening and
subsequent delay. The QRS width of the scalar lead II electrocardiogram
also showed biphasic changes, and the T wave amplitude progressively
decreased. Our results suggest that regional differences in repolarization
time may develop in the nonischemic myocardium in response to increased
extracellular potassium levels mainly as a result of local changes in
regional activation time rather than as a result of a direct effect on
action potential duration.
