Influence of Inversion of the Dog on the Electrocardiogram

Abstract

From the classical observations of Lewis 1 , 2 in dogs it has usually been inferred that the initial ventricular deflections of extrasystoles arising from the right ventricle are down in lead I and up in lead III, while those arising from the left ventricle are up in lead I and down in lead III. These observations were generally accepted in the interpretation of the human electrocardiogram until it was shown by Barker 3 that on stimulation of the human heart extra-systoles were produced which were opposite in character to those obtained in the dog.

We found in dogs with an experimentally produced chronic pericarditis that the initial deflection of ventricular extrasystoles may be reversed from the usual type described by Lewis. 1 , 2 In these experiments it was noted that the heart did not fall away from the anterior chest as is always the case in the normal animal, an observation which suggested that the change might be due to the fact that the heart was held in its normal anterior position when the chest was opened.

To test this hypothesis the following experiment was performed on 6 normal dogs. An animal was anesthetized and securely fastened on its back to a board. The chest and pericardium were opened in the usual manner. Electrocardiographic tracings were made and at the same time 7 points on the ventricle designated by Barker 3 were stimulated. The board was then turned over so that the animal was suspended with its anterior surface to the floor. This allowed the heart to fall against the anterior chest wall, was always accompanied by slight rotation of the heart to the right, and represented the more nearly normal position of the heart in the dog. Extrasystoles were again obtained by stimulating the identical 7 points. The animal was then placed on its back and the right bundle was cut. Electrocardiograms were taken in this position and also after inversion of the animal.