CLINICAL PROGRESS Digitalis and the Electrocardiogram By ALFRED PICK, M.D.

T HE action of digitalis and related glyco-sides is reflected in the electrocardiogram in a manifold fashion. Apart from altering the speed and mode of ventricular repolarization, represented by the ST-T portion, practically any type of disturbance in the formation or propagation of the cardiac impulse can result from digitalis medication; on the other hand some of these disorders of rhythm occurring spontaneously, may disappear on exhibition of the drug. Whether a therapeutic or a toxic effect will prevail, and the time until one or the other becomes manifest, depend on a number of variables and cannot be predicted in a given case. Whereas the dose and mode of administra-tion can be adjusted according to estimated needs, other factors that may largely influence the outcome of therapy are more difficult to assess in a clinical evaluation of the individual patient. This difficulty refers to the complexity of electrolytic disorders associated with con-gestive heart failure, the condition of the myo-cardium, and the speed and extent to which the glycoside is absorbed, metabolized, and ex-creted. It is for this reason that eachnew digitali-zation, and determination of a maintenance dose, should be viewed as a therapeutic experi-ment at the bedside, the outcome of which is uncertain. The decision to continue or to interrupt medication, and in what manner to change the basic therapeutic plan, will depend largely on the electrocardiographic control of the early therapeutic results. In table 1 the most common electrocardio-graphic manifestations of digitalis action are arranged from the viewpoint of their practical clinical significance, regardless of the various underlying physiologic mechanisms. Thus i