Influence on the Electrocardiogram of Changing Electrical Axis from Anterior to Posterior Mediastinum

The influence of position of the heart on the electrocardiogram has in recent years received considerable attention. That position of the electrical axis may be of importance was first emphasized by Lewis, 3 and the subsequent experiments of Katz and Barker 1 , 2 have indicated the importance of a more detailed study of the subject.

Kountz 4 has shown that placing hearts of dogs within the human pericardial cavity yield curves of a similar nature to those obtained in man. This is especially true when the dog heart has the same interthoracic relationship as that of man. Changing the position of the electrical axis will greatly influence the electrocardiographic curves. This observer has further shown that the dog's heart, readily movable from anterior to posterior mediastinum, yields markedly dissimilar curves when the position of the heart is altered anteriorly or posteriorly. These experiments have served to emphasize the importance of further investigation along these lines.

A dog heart-lung preparation was set up (Starling), and the heart and lungs removed from its body; the thorax of a cadaver, recently dead was opened anteriorly. The esophagus of the heart-lung preparation was connected by a wire to an electrode, which could be placed in any part of the human thorax. One chest electrode was placed in the left anterior chest wall; another in the right posterior wall, care being taken that these electrodes were equidistant from the midline of the chest. There were thus formed 2 vectors, one lying anteriorly, and the other posteriorly. The apex of the heart-lung preparation was connected to the esophagus in the chest. Finally, the 3 leads of the electrocardiograph were connected to the arms and left leg of the cadaver, by embedding the electrodes in the muscles.