ADVANTAGES OF THREE LEAD CARDIOGRAPHIC RECORDINGS *

In clinical practice it has become customary to record 12 ECG leads from each patient. This practice developed more by tradition than by biophysical reasoning. The number of ECG leads necessary to record the total information available from the body surface depends on the characteristics and complexity of the current source represented in this case by the heart and of the human body as a volume conductor. Einthoven’ treated the original bipolar limb leads as if they originated from a point-like current source. This is clearly indicated by his introduction of the “manifest QRS axis” and the Einthoven triangle. The mosb conveniently accessible parts of the human body, the extremities, were chosen as electrode sites. I t was obvious to Einthoven that voltage variations in the limb leads could be described as a vector, although the term was not used a t the time. The concept of the “manifest QRS axis” represented, however, the first significant step forward a unified concept in ECG lead display. This concept was developed further by Wilson and his coworkers-’ with the introduction of the ventricular gradient. Time integrals of limb leads were added vectorially and the entire electrocardiogram was expressed in one single term. Since only limb leads were used this representation remained limited to the frontal plane. The significance of “manifest QRS axes” and the ventricular gradient go even beyond the introduction of vector concepts in electrocardiography. These terms represent classical examples of data reduction which has become of increasing importance in the present era of electronic data processing. Construction of a frontal plane QRS axis in the Einthoven triangle makes it very obvious that only two leads are necessary to obtain this axis. Additional leads cannot contribute any new information and are, therefore, redundant. Recording of more than two limb leads could have become obsolete after Einthoven’s description of the “manifest QRS axis”. Development of such unifying concepts of lead design and data display were interrupted by the introduction of unipolar ECG leads. They were thought to record primarily from limited portions of the myocardium underlying the electrodes. This new concept changed the further development of electrocardiography drastically. No impelling need was felt any more to