Effect of potassium and calcium deficiency on the monophasic action potential, electrocardiogram and contractility of isolated rabbit hearts

Abstract

Isolated rabbit hearts were perfused with Krebs-Henseleit solution deficient in K, Ca or both. Ventricular monophasic action potentials registered with the suction electrode, electrocardiograms and intraventricular pressures were recorded simultaneously for periods up to 20 minutes. Perfusion with K-deficient solutions resulted in a brief initial prolongation of the entire descending limb of the action potential and of the T wave, followed by progressive increase in slope of the initial portion and decrease in slope of the terminal portion of the action potential. During this time the T wave became shorter and a U-wave-like deflection occupying the entire diastole developed. QRS showed progressive prolongation. Finally, A-V conduction disturbances, ectopic beats and ventricular fibrillation developed. The force of contraction increased slightly. Perfusion with Ca-deficient solutions decreased the slope of the initial portion while increasing the slope of the terminal portion of the action potential. This was accompanied by prolongation of the ST- segment and reversal in the direction of the T wave. The duration of the action potential reached a maximum after 40–80 seconds of perfusion, while the force of contraction decreased progessively. Perfusion with solutions without potassium and calcium prolonged the initial as well as terminal portion of the action potential.