Formation of a border ischemic zone depends on plasma potassium
concentration.
Abstract
In the border zone of ischemic myocardium, extracellular potassium
concentration ([K+]) gradually decreases from the ischemic to normal
area. Since blood [K+] is equilibrated with the normal tissue
[K+], it might affect the [K+] and modify electrophysiological
properties in the border zone. The study aimed at evaluation of
distribution of depolarization and repolarization characteristics across
the ischemic-normal border under blood [K+] variation. 64-lead
epicardial mapping was performed in 26 anesthetized rats with [K+]
ranged from 2.3 to 6.4 mM in an in vivo model of acute
ischemia/reperfusion. The animals with [K+]<4.7 mM
(low-normal potassium) had a typical ischemic zone with ST-segment
elevation and activation delay, a border zone with ST-segment elevation
and no activation delay, and a normal zone without electrophysiological
abnormalities. The animals with [K+] >4.7 mM
(normal-high potassium) had only the typical ischemic and normal zones
and no transitional area. Activation-repolarization intervals and local
conduction velocities were inversely associated with [K+] in linear
regression analysis with the adjustment for a zone of myocardium. The
reperfusion extrasystolic burden (ESB) was greater in the low-normal as
compared to normal-high potassium animals. Ventricular
tachycardia/fibrillation incidence did not differ between the groups. In
patch-clamp experiments, hypoxia shortened action potential duration at
5.4 mM but not at 1.3 mM of [K+]. The IK(ATP) current was lower at
1.3 mM than at 5.4 mM of [K+]. The formation of the border zone was
associated with attenuation of IK(ATP) response to hypoxia in low-normal
[K+] and increased ESB at reperfusion.