Abstract
No interpretation of a given phenomenon can be considered final until verified by its application to reproduce that phenomenon. Such a demonstration has hitherto not been available to elucidate the mechanism and pathways of cardiac excitation. The problem may be simplified by a technical isolation of the several regions of the heart. Whereas in the standard leads, the excitation process manifests itself in toto, it is possible, by the application of direct contacts to the surface of the heart, to recognize the behavior of regions immediately subjacent to these contacts. Using simultaneous records by 3 galvanometers of equal resistance and string periodicity, one may compare the response of each locus to stimuli approaching it from one of several directions, to ascertain under what circumstances its intrinsic deflections most accurately recapitulate the normal.
In this instance 2 electrodes were placed on the left border of the heart in line with the fibre direction of the superficial bulbo-spiral muscle. Electrode “A” at the apex was connected with “B” at the base by lead I, and each with the left leg, “L.L.”, as leads II and III respectively; all three being recorded simultaneously. The contour of the spontaneous beats of the heart (exposed in a dog after pentobarbital anesthesia) is shown in the cycles marked “N” in Fig. 1. Electrical stimulation of the apex at a point very near to contact A initiates a premature systole (cycle “A”, Fig. 1) with intrinsic deflections having the same direction as the normal in every lead. A very different result is obtained by retrograde excitation of the muscle from a stimulus introduced at the point B on the base of the heart; both leads I and III from this region are the inverse of normal.
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