After-potentials in the electrocardiogram.

Abstract

Summary.An analysis has been made of the lingering potentials following the T‐wave in the electrocardiogram, as previously described (Sjöstrand, 1950). A positive after‐potential can be recorded both by the usual electrocardiograph with an alternating current amplifier (Triplex, Blema), and by means of a direct current amplifier, cathode ray oscillograph and subcutaneous needle electrodes.On intravenous infusion of small amounts of adrenaline, the after‐potential is greatly increased. It may be shown that it is continuous with a component, which, in the normal resting electrocardiogram, is included in the T‐wave. Increased vagus tonus appears to have the opposite effect to that of adrenaline. The typical electrocardiographic changes occurring with lowered blood potassium concentration correspond in several respects to the adrenaline effect.The positive after‐potential is not directly connected with the mechanical systole of the heart and it occurs either completely, or to the greater extent, after the refractory period. During this phase there seems even to be an increased excitability, judging from the fact that extra‐systoles may occur.The after‐potentials and their variations show a great similarity to those of nerves, Purkinje fibres and the isolated frog heart. They may explain several physiological changes in the electrocardiogram. A number of pathological deviations may also be explained from variations in these after‐potentials and so be considered in relation to the recovery processes in the myocardium following the actual action potential.