The relationship between the anatomic position of the heart and the electrocardiogram; a criticism of unipolar electrocardiography.

Using a method for identifying precisely the lie of the ventricular structures in the body at autopsy , the anatomic position of the heart was compared with the directions of the QRS electrical forces in a large number of subjects with and without heart disease. While the mean QRS axis varied through 180 degrees in these subjects, the anatomic position of the left ventricle varied less than 45 degrees. No instances of significant rotation of the heart around its long axis were encountered, and it is shown that the unipolar electrocardiographic criteria for position and rotation of the heart have little validity. An explanation for the axis deviations of ventricular hypertrophy is offered. T HAT the form of the QRS complex is influenced by the position of the heart in the chest has been known since Einthoven demonstrated changes in the direction of the mean QRS axis with respiration. Later, the introduction of unipolar precordial leads made it possible to study the relationship between the electrocardiogram and position of the heart in three-dimensional space, and Wilson and co-workers devised a method for recognizing five different heart positions from combinations of QRS complexes in the unipolar limb and precordial leads.' Subsequent workers have greatly extended this method in order to define in more detail the position of the heart and its components from the electro-cardiogram. Wilson's method was the outgrowth of a particular hypothesis regarding the factors which govern the form of the QRS complex. On the basis of experiments performed by Lewis and in his own laboratory, Wilson concluded that the unipolar lead might be considered to resemble a "direct lead," that is, one placed directly on the heart and recording principally the electrical events of the portion of the heart underlying it.2, This hypothesis 890 suggested that when a unipolar electrode faced a particular region of the heart it would write a QRS complex with a specific contour for that region, and there would be specific QRS patterns for many different regions of the heart. Thus, when a particular QRS contour was seen in one or another unipolar lead, it could be concluded that the region of the heart known to yield that QRS pattern must be facing that electrode location. This hypothesis has been extensively applied to clinical electro-cardiography and detailed systems have been devised for detecting various types and degrees of rotation of the heart, the lie …