Origin of body surface QRS and T wave potentials from epicardial potential distributions in the intact chimpanzee.

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Abstract
Epicardial and body surface QRS-T wave potential distributions were measured during normal and ectopic sequences in intact chimpanzees. Epicardial potential distributions were used because they provide a comprehensive picture of total cardiac electrical activity for relating heart and body surface events during both ventricular activation and repolarization. When the epicardial potential gradients existed over a distance greater than that to the recording points on the body surface, e.g., as occurred during the overlap of terminal ventricular activation and early repolarization, the epicardial events were mirrored well on the anterior chest surface. However, when the recording points were at a distance greater than that over which the epicardial potential gradients existed, the details of the epicardial events disappeared and their effect was to produce distinct changes in the low-level potentials over broad distant areas. The major manifestations on the body surface of selective epicardial events frequently were changes in the distant low-level potential areas while there was no change in the pattern near the maximum or minimum. The ST-T wave body surface distributions were as useful as the QRS patterns for localizing the ventricular ectopic foci presented. A direct experimental basis is provided for explaining T wave notches which occurred during normal and ectopic beats and resembled U waves. It should be possible to achieve as precise an understanding of ST-T waves on the basis of epicardial potential distributions as has thus far been achieved for QRS on the basis of isochrones.