The effect of certain pure digitalis-like glucosides on the frog's heart

Monophasic action potentials in man

Monophasic action potentials with an amplitude of up to 70 mv were recorded with suction electrodes from the endocardial surface of the right atrium and both ventricles during diagnostic cardiac catheterization. The method was simple and safe. The monophasic action potential of human beings had the same shape and the same relation to the electrocardiogram as the transmembrane action potential of animals has. Also changes in heart rate and administration of calcium and digitalis had the same effect on the monophasic action potential of man as on the transmembrane action potential of animals.

When injections of contrast material into the coronary arteries produced T-wave changes, the monophasic action potential from the ventricle perfused by the contrast medium lengthened, but the monophasic action potential from the other ventricle did not change.

Our study suggests that the monophasic action potential may be helpful in estimating the refractory period at the site of recording and in explaining the pathogenesis of abnormal repolarization in the electrocardiogram.

The Nature of the RS-T Segment Displacement as Studied with Esophageal Leads

The electrocardiographic changes, with particular reference to the RS-T segment and T wave, in surface leads and in esophageal leads reflecting left ventricular cavity potentials, are studied in 7 persons with and without heart disease, before and after the administration of digitoxin. After the administration of digitoxin, the RS-T segment depression in precordial leads and in esophageal leads reflecting the potentials of the posterior surface of the left ventricle, are regularly associated with RS-T segment elevation in esophageal leads reflecting left ventricular cavity potentials. The possible roles played by myocardial involvement due to digitalis, modification of the monophasic curves, and the reduction of the human ventricular gradient are discussed.