Correlation of the Electrophysiological and Mechanical Changes in the Dog Heart during Digitalis Administration, and the Effect of Potassium on It

The present investigation was designed to study the relationship between mechanical and electrophysiological actions on the heart of digitalis and the effects on it of K administration. Nineteen anesthetized dogs were given acetylstrophanthidin (AS) (30 gamma/Kg, followed by 1 gamma/Kg/min. When ectopic tachycardia occurred, sinus rhythm was restored with an infusion of K (5 mEq/Kg/hour, for 5 min). As the dose of AS was increased beyond 30 approximately 40 gamma/Kg, ventricular rate during electrically induced atrial fibrillation was reduced and PQ interval prolonged, while PP interval, QT interval and QRS duration showed little changes. Ectopic tachycardia occurred at an average dose of 56.9 gamma/Kg of AS. The indices of mechanical properties, dp/dt/IIT, max dp/dt and dp/dt (50), began to increase as soon as AS infusion was started and continued to increase during the administration of AS. The dp/dt (50) and PP interval or ventricular rate during atrial fibrillation did not change in parallel. Inotropic activity was not depressed even during ectopic tachycardia. The administration of K eliminated ectopic tachycardia, but caused no changes in the other electrophysiological and mechanical properties of the digitalized heart. The following conclusions were derived from the experiment. 1) The 2 actions of digitalis, mechanical and electrophysiological ones, are not necessarily related to each other. 2) Digitalis intoxication, represented by ectopic tachycardia, does not mean the depression of the inotropic activity. 3) The administration of K does not affect the inotropic activity of digitalis.