The effect of changes in concentration of cations on the electrocardiogram of the isolated perfused heart

Abstract

Action potentials were recorded simultaneously from the cavity and the epicardium of the ventricle of the isolated perfused hearts of the dog and the turtle before and after alteration of the concentrations of the various cations in the perfusate. The major effects of an excess of potassium on the turtle heart were similar to those on the heart of the dog (prolonged QRS interval, shortened S-T interval, broad P waves, and terminally monophasic or diphasic complexes). However, in the turtle heart the atria and sinus venosus were more tolerant than the ventricle to an excess of potassium; both mechanical contraction and electrical activity of the atria persisted after complete ventricular arrest, while in the dog both mechanical and electrical activity of the atria ceased long before that of the ventricles. An increase in the amplitude of the T wave was observed in the dog and turtle hearts under the influence of an excess of potassium; the width of the T wave was increased or remained the same. The addition of extra calcium to a perfusate containing an excess of potassium lessened the delay in intraventricular conduction and further shortened the S-T interval produced by the excess of potassium. Restoration of a low sodium concentration to normal partially reversed the alterations in the electrocardiogram characteristic of an excess of potassium. In the turtle heart a reduction of the sodium concentration in the presence of an excess of potassium enhanced the effects of the latter. Increase of the sodium concentration in the presence of an excess of potassium partially antagonized the effects of the latter. Complete absence of potassium from the perfusate prolonged the P-R interval, prolonged the QRS interval, prolonged the S-T interval, and widened the T waves in the turtle heart. Except for slight or no widening of the QRS complex before atrioventricular dissociation developed, similar changes took place in the dog heart when the perfusate contained no potassium. The electrocardiographic changes in the dog heart were consistent with those found in cases of human beings with hypopotassemia.