Effects of some components of ischemia on electrical activity and reentry in the canine ventricular conducting system.

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Abstract
We used intracellular microelectrodes to study the electrophysiological effects of combinations of components of ischemia and their relation to the occurrence of ventricular arrhythmias in the specialized conducting system of isolated canine right ventricles. The middle area of the free wall was exposed to various test solutions in the center compartment of a three-chambered bath; the base and apex of the preparation were superfused with normal Tyrode's solution in the outer control compartments. Hypoxia (Po2 40 mm Hg), lactic acidosis (pH 6.5), and orciprenaline (10(-6) M), either alone or combined, failed to affect the action potential amplitude or the conduction velocity of the subendocardial fibers, and no arrhythmias occurred. The action potential duration and the effective refractory period were markedly prolonged by lactic acidosis. Exposure of the test regions to 15 mM K+ plus orciprenaline resulted in marked decreases in action potential amplitude and conduction velocity. Abnormalities of impulse transmission through the depressed area included high degrees of rate-dependent block, one-way block, warming-up phenomenon, and the Wenckebach phenomenon. Such conditions regularly provoked the appearance of single, sustained, or concealed reentrant depolarizations. The combined effects of hypoxia, 15 mM K+, and orciprenaline resulted in further depression of the already depressed action potential in the depolarized fibers. Our results indicate that regional increases of extracellular K+ may be the predominant factor of the components of ischemia we studied which facilitates the initiation of reentrant arrhythmias.