KEYWORDS
border zone, myocardial ischemia, potassium, epicardial mapping, action
potential duration, potassium ionic currents
INTRODUCTION
Acute regional myocardial ischemia leads to the development of
myocardial regions with different properties: an ischemic zone in the
nonperfused myocardium with metabolic and electrolytic disturbances, a
normal zone in the perfused area with unchanged properties, and a border
zone with mild transitional changes located in the perfused area between
the normal and ischemic zones. The border zone is thought to play an
important role as a substrate and a source of triggers for
arrhythmias1-3.
The ischemic zone characterized by a local increase in extracellular
potassium concentration ([K+]) (“local hyperkalemia”). The
excessive K+ leak from the affected cells and its accumulation in the
extracellular space 4 are caused by the opening of the
ATP-dependent potassium channels 5, 6 and inhibition
of Na,K-ATPase 7 in conditions of the depletion of
ATP. The increased extracellular [K+] gradually declines in the
direction from the ischemic to normal myocardium 8-11.
In such a case, [K+] in the transition zone depends on the K+ efflux
from the ischemic zone and the [K+] in the normal zone, which is
equilibrated with a plasma [K+] level.
Extracellular [K+] influences the major parameters of the action
potential such as its duration, resting membrane potential (RMP), and
dV/dt max 12. Hypokalemia and hyperkalemia lead to the
decrease or increase in K+ channel conductance, lengthening or
shortening of action potential duration (APD), hyperpolarization or
depolarization of RMP, respectively. Both disturb myocardial conduction
and repolarization and promote ventricular arrhythmias. The low
(<3.5 mM) and high (≥4.5 mM) serum [K+] levels are known
to increase the risk of ventricular fibrillation (VF) and mortality of
patients with myocardial infarction 13.
Inhomogeneity of electrophysiological properties of myocardium is one of
the major prerequisites of arrhythmogenesis, and the ischemia-related
spatial differences of the extracellular [K+] promote action
potential heterogeneity and electrical instability in the heart.
Since blood [K+] affects [K+] in the myocardial tissue, the
ischemia-related myocardial electrical heterogeneities might be modified
in hypo- or hyperkalemic conditions. The aim of the present study was to
evaluate the effect of the variation of blood [K+] level on the
distribution of depolarization and repolarization characteristics across
the ischemic, border and normal zones and to test them for the
association with arrhythmic outcomes.
RESULTS