NATURE OF THE PRECORDIAL ELECTROCARDIOGRAM

Abstract

Exploring the surface of the heart in 15 dogs by means of (a) injury produced by topical application of isotonic KC1, (b) the influence on the T wave of local warming and cooling, and (c) the configuration of electrically induced extrasystoles as recorded in the chest leads, it was concluded that (1) the precordial electrocardiogram represents the interference of opposing electrical forces developing with the excitation and recovery of specific regions which are proximal and distal with respect to the position of chest electrode. An intermediate zone rather large in extent separates the proximal and distal zones of each lead. Potentials derived from the excitation of this zone fail to be reflected in the precordial ecg. (2) The downstrokes of Q, R, and S are caused by preponderance of excitation in proximal areas. The upstrokes of Q, R, and S are caused by preponderance of excitation in distal areas. (3) The T wave is similarly derived from differences in the time and rate of recovery from excitation in distal and proximal zones. An upright T wave indicates beginning of repolarization in the proximal zone in advance of the distal region, while an inverted T indicates that regions in the distal zone begin to repolarize in advance of the proximal zone. The S-T segment is elevated when injury is present in the proximal zone, and depressed when injury occurs in the distal area. (4) Injury to the large intermediate zone cannot be detected in the precordial ecg. The proximal and distal zones for 3 different leads (CR, CF and CV) were detd. in the dog when the chest electrode was placed external to the left and right apex.