A study of methods of making so-called unipolar electrocardiograms

Abstract 1. 1. The reason given by Eckey and Frohlich for stating that unipolar electrocardiograms can be obtained by their procedure of immersing the body in distilled water and surrounding it by a copper network which is also in the water bath, with one electrode on a body area paired with an electrode attached to the network, has been subjected to experimental test. Evidence is furnished that this reason is not valid. There is, consequently, no ground for believing that unipolar electrocardiograms can be obtained by such a method. 2. 2. The central terminal procedure of Wilson for making unipolar leads has been subjected to study. 2.1. A. The good agreement which is said to exist between Wilson's central terminal procedure and Eckey and Frohlich's immersion procedure, a point made by Wilson in support of his method, does not demonstrate the validity of the central terminal procedure because the principle underlying the immersion procedure is unsound. 2.2. B. The various assumptions which have to be made if the central terminal procedure is to be regarded as valid as a method for making unipolar leads were compared with the assumptions which have to be made to establish the method of balanced potentials (or its simpler but slightly less accurate substitute of pairing the exploring electrode with one placed over the spine of the right scapula) as a procedure for (1) making unipolar leads, or (2) reducing interference with the potential variations of the exploring electrode. Certain observations regarding the distribution of potential on the surface of the body cannot be accounted for on the basis of the assumptions which must underlic the central terminal procedure. No such difficulties were encountered regarding the less elaborate assumptions underlying the other procedures. 2.3. C. Certain comparisons of results obtained by the central terminal method and by pairing the exploring electrode with one placed over the spine of the right scapula have been made. (1) The latter procedure shows the phenomenon of decrement with preservation of pattern as the exploring electrode is moved away from the heart along certain lines far better than does the central terminal method; (2) the correspondence of patterns of difference of potential recorded by parring electrodes across the attachments of the right and left arms with the patterns obtained by placing one electrode on the arm of the same side and the other on the spine of the right scapula is far closer than the “unipolar” patterns of arm potential obtained by the central terminal method, and (3) a negatively directed deflection recorded early in the QRS complex by the central terminal procedure at the C1 position in most cases of right bundle branch block is recorded as a very small deflection, or not at all by the RS procedure. This deflection, unlike other parts of the QRS complex, is not subject to decrement as the exploring electrode is moved away from the heart. All the evidence indicates that it is derived from the central terminal. Moreover, if the assumptions which must underlie the central terminal procedure are valid, it is impossible to account for the derivation of such a deflection from either the central terminal or the exploring electrode. 3. 3. The evidence presented indicates that, by pairing an exploring electrode with one placed over the spine of the right scapula, less interference with the potential variations of the exploring electrode occurs than in the case of methods which have been called unipolar. The bearing of this conclusion, if it be valid, on methods used in clinical electrocardiography is obvious.