Effect of potassium and toxic doses of digitalis on the myocardium.

This study was designed to evaluate further the antagonism between digitalis and potassium. Potassium was given by intravenous infusion to six dogs (1) before digitalization, (2) after injection of "therapeutic" doses of digitoxin, and finally (3) after injection of "toxic" doses of the drug. P OTASSIUM is used in the treatment of cardiac arrhythmias thought to be due to toxic effects of digitalis. 1 ""' In an effort to study the presumed digitalis and potassium "antagonism" the latter was administered to "fully" digitalized patients with atrial fibril-lation with or without ventricular ectopic beats. 0 The result was one of depression of both the conduction through the A-V node and of ventricular ectopic beats and the electro-cardiogram suggested increased rather than diminished effect of digitalis. This effect was short-lived and disappeared either with slowing or cessation of infusion. In a subsequent observation a severe toxic reaction to potassium , manifested by complete A-V dissocia-tion witli reverse AVenckebach phenomenon, was observed in an overdigitalized patient in whom the same procedure prior to digitaliza-tion caused no delay of conduction.' The present study was undertaken to elucidate further the relation between intravenously administered potassium and digitalis, using dogs intoxicated with digitoxin. Eighteen experiments were performed on 6 mongrel dogs weighing S to 12 Kg. The animals were anesthetized with 30 ing. of sodium pento-barbital per Kg. of body weight given intraperi-toneally. The infusion contained 155 mEq./L. of potassium as buffered phosphate salts in distilled water. The solution was injected at a rate of 4.0 ml. or 0.69 niEq. of potassium per minute, the uniformity of administration being assured through the use of a flownieter. In experiments 1, 4, 5, 9, 10, 13, and 14 (table 1) the infusion was discontinued after a total of 2 inEq. and in experiment 7 after 0.3 niEq./Kg. of potassium was administered. In subsequent trials the injection was continued until A-V block (table 1, exper. 6, 16, 17), supraventrieular arrhythmia (table 1, exper. 2, ]]) or cardiac standstill (table 1, exper. 3, 8, VI, 15, 18) appeared. The amount of potassium never exceeded 3 mEq./Ivg. The electrocardiogram was i.ionitored continuously, using an oscilloscope. All permanent tracings were recorded with direct writing equipment using standard lead II connections. After a control cardiogram was taken, further records were made whenever any change was observed on the oscilloscope. At the end of the control infusion , digitoxin in doses of 0.2 or …