The effect of posture on the form of precordial leads of the electrocardiogram

Abstract

1. 1. Chest leads were taken with subjects in three positions: supine, sitting, and lying on the left side. 2. 2. Three precordial leads were used. In one, the exploring electrode was placed in the midsternal line at the level of the fourth intercostal space (Chest Lead A); in the second, halfway between this point and the apex (Chest Lead B); and in the third, at the apex (Chest Lead C). In each case, the indifferent electrode was in the interscapular region. 3. 3. Forty-one observations were made on sixteen patients. The group included normal subjects and patients with heart disease. Among the latter were patients with right, and others with left, ventricular preponderance. In three patients the position of the heart was relatively fixed. 4. 4. The variations in the form of the chest lead with change in the patient's posture are described. They consisted chiefly of a decrease in the amplitude of the R and T waves, which varied concordantly, and, in many cases, a decrease in the amplitude of the S waves, as the subject's posture was changed from supine, to sitting, to lying on the left side. In several cases positive T waves became diphasic and diphasic T waves became negative. 5. 5. Although these changes occurred in each of the three chest leads, they were most marked in Chest Lead C (electrode at apex). 6. 6. The changes cannot be predicted with any certainty in individual cases. 7. 7. The importance of considering the patient's position when taking chest leads, and of taking them in the same position each time in order to make them comparable, is pointed out.