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1 Department of Biomedical Sciences, Cornell University, Ithaca, New York 14853-6401; and 2 Department of Medicine, University of Würzburg, D-97074 Würzburg, Germany
To
test whether hyperkalemia suppresses ventricular fibrillation (VF) by
reducing the slope of the action potential duration (APD) restitution
relation, we determined the effects of the extracellular K+
concentration ([K+]o) ([KCl] = 2.7-12
mM) on the restitution of APD and maximum upstroke velocity
(Vmax) the magnitude of APD alternans and
spatiotemporal organization during VF in isolated canine ventricle. As
[KCl] was increased incrementally from 2.7 to 12 mM,
Vmax was reduced progressively. Increasing
[KCl] from 2.7 to 10 mM decreased the slope of the APD restitution
relation at long, but not short, diastolic intervals (DI), decreased
the range of DI over which the slope was 
1, and reduced the maximum
amplitude of APD alternans. At [KCl] = 12 mM, the range of DI over
which the APD restitution slope was 1 increased, and the maximum
amplitude of APD alternans increased. For [KCl] = 4-8 mM, the
persistence of APD alternans at short DI was associated with
maintenance of VF. For [KCl] = 10-12 mM, the spontaneous
frequency during VF was reduced, and activation occurred predominantly
at longer DI. The lack of APD alternans at longer DI was associated
with conversion of VF to a periodic rhythm. These results provide
additional evidence for the importance of APD restitution kinetics in
the development of VF.
action potential duration; extracellular potassium concentration
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