The Nature of the RS-T Segment Displace- ment as Studied with Esophageal Leads III. The Effects of Digitalis

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. C HANGES in electrocardiograms of ani-mals and humans induced by digitalis were reported upon shortly after intro-duction of the string galvanometer, ' 2 but it was not until the publications of Cohn and co-workers3-5 that the significance of the T wave alterations due to digitalis was emphasized. Sub-sequently, other investigators published their observations of the changes in the T wave and RS-T segment in the three standard leads in both normal and diseased hearts, using varying doses and different preparations of digitalis.6-8 A regular sequence of changes in the T wave and RS-T segment induced by digitalis was de-scribed by McMillan and Bellet in 1932.9 These changes consisted essentially of progressive lowering of the height of the T wave with subsequent depression of the RS-T segment, and finally diphasic or inverted T waves. These authors also observed that smaller doses of digitalis were required to produce T-wave and RS-T segment changes in the electrocardio-grams of older persons, especially with diseased hearts, than in young persons.'0 The electro-cardiographic changes in the precordial leads due to digitalis have been described in several reports."1-'