The Positive Inotropic Action of Cardiac Glycosides on Cardiac Ventricular Muscle

Abstract

The positive inotropic effect of cardioactive steroids is the consequence of an acceleration of the force development during contraction, i.e., of a positive klinotropic effect. This was demonstrated probably for the first time by W. Straub (1908) when he recorded the intraventricular pressure development during systole by a suitable method. He observed that the velocity of the rise of the intraventricular pressure was increased under the influence of digitalis, and that, accordingly, the isometric contraction phase was shortened (Fig. 1 a). He concluded that the elementary action on the heart of digitalis is to make the ventricle contract faster („Als Elementarwirkung der Digitaliskörper auf das Herz dürfte also die anzusehen sein, daß sich der Ventrikel rascher zusammenzieht“). These observations were extended two years later by Magnus and Sowton (1910) who recorded complete isometric contraction curves of the left ventricle of the isolated cat heart. Their tracing (Fig. 1 b) shows that, because of the greater speed of the force development under the effect of the glycoside, the height of the contraction curve, representing the peak force of the isometric contraction, was increased.