Effect of Altering Position of the Heart on the Voltage of Electrocardiogram.

Abstract

Rotation of the heart of the dog in situ upon its longitudinal or antero-posterior axes alters the direction of the QRS complex of the electrocardiogram. 1 Altering the position of the heart in this manner or shifting the points of the leading about the heart as has been done by other investigators, however, maintains unchanged the relation of the heart to the plane which is defined by the points of the triangle from which the leads are taken.

Altering the long axis of the heart with reference to this plane ought to affect the voltage of the curve for the following reason: In the schema of Einthoven the heart is considered as a simple potential difference between 2 points. It is represented as the line between these points (the electrical axis). This line normally corresponds in an approximate manner to the long axis of the heart. The voltage of the electrocardiogram is recorded from the points of the Einthoven triangle, and is therefore proportional to the perpendicullar projection of the line representing the electrical axis of the heart to the sides of the triangle (or to the relation between the absolute potential difference developed by the heart and the cosine of the angle between the direction in which the potential is developed and the line of lead). For similar reasons, if the heart is rotated in the plane perpendicular to that defined by the 3 points of the triangle, i. e., on the transverse axis of its base, the voltage registered by all 3 leads will diminish in proportion to the angle of inclination between the plane of the leads and the electrical axis. When they are parallel the voltage registered is maximum, and when they are perpendicular it is minimum, without regard to the relations already existing between them within the plane of the leading.