. A text-book of physiology : for medical students and physicians . a wave Q below the line, which would indicate an * For a description of the Electrocardiogram and the literature consultJames and Williams, American Journal of the Medical Sciences, Nov., 1910,or Kraus and Nicolai, Das Elektrokardiogramm, Leipzig, 1910. THE HEART BEAT. 543 excitation toward the apex of the heart. The interpretation of Qhas not been made satisfactorily, but in accordance with the ana-tomical arrangement of the auriculoventricular bundle referred toin the last paragraph it is possible that it indicates that the
. A text-book of physiology : for medical students and physicians . a wave Q below the line, which would indicate an * For a description of the Electrocardiogram and the literature consultJames and Williams, American Journal of the Medical Sciences, Nov., 1910,or Kraus and Nicolai, Das Elektrokardiogramm, Leipzig, 1910. THE HEART BEAT. 543 excitation toward the apex of the heart. The interpretation of Qhas not been made satisfactorily, but in accordance with the ana-tomical arrangement of the auriculoventricular bundle referred toin the last paragraph it is possible that it indicates that the initialexcitation in the ventricle starts in the fibers of the papillary mus-culature near the apex. Q is immediately followed by the largewave R, which indicates an excitation at the base of the ventricles,followed by a rapid transition to the opposite phase S, as thisexcitation passes to the apex of the ventricle. The wave T,occurring at the end of the ventricular systole, has been difficult tointerpret. According to one view* it indicates that the wave Fig. 227.—Electrocardiogram obtained by photographing the movements of thethread of a string-galvanometer. The upper figure shows the photographed curve, whilethe lower one is a diagram constructed from the photograph to make clearer the electricalchanges in a single cardiac cycle. To obtain this record the electrodes were connectedwith the right and left hands. Waves with the apex upward indicate that the base of theheart (or the right ventricle) is negative to the apex (or left ventricle). Waves with theapex downward have the opposite significance. Wave P is due to the contraction of theauricle. Waves Q, R, S, and T occur during the systole of the ventricle. (Einthoven). of excitation passes last to the basal portion of the ventricle, andconsequently that the contraction of the ventricle terminatesat this point. This conception is in harmony with the embryo-logical fact that the ventricle develops originally from a
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