The effect of therapeutic doses of digitalis on the contraction of heart muscle

That digitalis causes alterations in the heart resulting in changes in the form of the electrocardiogram is now well known. Robinson and Wilson have estimated in experiments on cats that the quantity of digitalis which can induce a change is about 30 per cent, of the calculated lethal dose. So far, however, no evidence has been presented to show that this amount of digitalis is beneficial—except in cases of fibrillation of the auricles in which block of auricular impulses, mainly through stimulation of the vagus nerves, takes place. A beneficial action must be based on the ability of the drug to increase the volume output of the heart, and it must be able to do this in therapeutic doses, that is to say, in doses which influence the T wave of the electrocardiogram or reduce the rate in auricular fibrillation. We have accordingly injected this amount into the veins of dogs, 11 of which received the tincture of digitalis and 19 of which received g-strophanthin; and into cats, 5 of which received g-strophanthin, and 9, the tincture of digitalis. Alterations in volume output were studied in curves obtained by the use of the Roy and Adami myocardiograph. The curves represent longitudinal linear alterations in the form of ventricles and may, under the conditions of cardiac contraction, represent changes in volume of the cavities and consequently of volume output. The results are reported as changes in the degree of contraction. The animals were anesthetized with ether only. The chest was opened in the median line. Other details of the technical procedure, which are important, will be given in the full report of these experiments. The significant results concern the effect of these two drugs on the T wave and on the degree of contraction (Table I).