ELECTROCARDIOGRAPHY 



339 



bipolar leads is the derivation of parts of the heart by 

 recording partial derivatives or proximity potentials. 

 We may call such systems "local leads." The nature of 

 their electrical arrangement favors use of multipolar 

 systems as total leads and bipolar or unipolar systems, 

 as local leads. 



Total or Heart \ cctor Leads 



BIPOLAR DERIVATIONS IN ONE PLANE. The most Com- 

 mon leads of this type are the classical Einthoven 

 extremity leads, put on both arms and the left leg 

 and usually marked with the letters R, L, F. Under 

 "ideal" conditions, the projection laws are those 

 demonstrated in figure 18.-I. More realistic conditions, 

 however, as revealed by a homogeneous torso model, 

 lead to a correction: the Burger triangle (126, 142, 

 524). This triangle, for a single case given in figure 

 1 85, consists of the three lead vectors of the extremity 

 leads and is vaHd for one single heart vector in a fixed 

 location. The length of each side of the triangle repre- 

 sents the amplitude factor: the recorded potential is 

 the scalar product of this length, as a vector, and the 

 projection of the heart vector. This means, regarding 

 figure 18 B, that in lead I (R to L) the recorded heart 

 vector is relatively much smaller than that in the 

 other leads. The reason apparently is that the points 

 which mark the real electrode positions are the region 

 where the extremities join the thorax; these points do 

 not actually form an equilateral triangle. 



It is a physical platitude that in the Einthoven tri- 

 angle the sum of all leads I -\- II -\- III equals zero 

 for each moment. (That II is ordinarily introduced 

 with its negative value stems from the inverse polarity 

 which the common technique uses to record this 

 lead.) This remains true for the Burger triangle as 

 well, so that the three lead vectors form a closed geo- 

 metrical figure, if put together. 



The Einthoven and Burger triangles only record 

 the heart vector projections in the frontal plane, if 

 one disregards a slight inclination of the plane of the 

 triangle away from the frontal plane. There is a second 

 lead system for recording in a single plane, the Nehb 

 triangle (356), the electrode positions of which are the 

 sternal end of the right second rib (R), the projection 

 of the heart apex on the left posterior axillary line 

 (L), and the heart apex (F). The long axis of the 

 heart lies in the plan thus formed. A horizontal triangle 

 has been described by Blasius (i 12). Yet it is question- 

 able whether derivations like those of Nehb really are 

 total heart vector leads, because, in the clinical use of 

 the Nehb triangle, it seems to pick up preferably 



events, such as infarcts, in the posterior wall of the 

 heart. The explanation could be that the lead line RL 

 in Nehb's triangle is minimally represented in other 

 lead systems, but lies in the direction of all vectors 

 developing after local disturbances in the posterior 

 part of the left ventricle. Such events would naturally 

 be evidenced in a total heart vector, but would project 

 themselves minimally in an orthogonal lead system. 



THREE-DIMENSIONAL BIPOLAR SYSTEMS. All Other lead 



systems of the bipolar type are oriented three-dimen- 

 sionally. In order to compare and describe these 

 systems, it is first necessary to discuss the nomencla- 

 ture. The three axes in space, x, y, and z, are directed 

 as indicated in figure 19. There are other symbols 

 used as well, but in this paper we should like to adopt 

 these. The electrodes vary both in their craniocaudal 

 and their circumferential position. The lead vectors 

 thus achieved must be described by their magnitude 

 and their elevational and azimuthal angles (see fig. 

 58). The elevational angles are designated in accord- 

 ance with the usual Einthoven angle a, which is 

 negative upward. The positions anatomically fixed 

 for certain standard leads will be mentioned later. If 

 a rotation is to be described appropriately, a conven- 

 tion must be established regarding the side of the 

 plane to be viewed (248). In this chapter the notations 

 are such that the frontal plane is viewed from the 

 front, the sagittal plane from the left, and the hori- 

 zontal plane from above the patient (390). (See 

 table lb.) 



Several attempts have been made to determine the 

 sagittal component of the heart vector, the most 

 prominent of which are the two cubic systems of 

 Duchosal & Sulzer (15) and Grishman & Scherlis 

 (28), and the Wilson tetrahedron (163, 527) (fig. 20). 

 These systems show rather considerable deviations in 

 their respective potential differences and patterns 

 even in analogue derivations (198), and the devia- 

 tions in the torso model are, with the best system, 

 (Wilson's tetrahedron) as much as 15 per cent! There 

 are, however, more optimistic voices (306), A system 

 which offers some advantages is the Gondorelli sys- 

 tem, the lead axes of which coincide with the axes 

 of symmetry of the electrical heart field (480). What- 

 ever the situation might be, the "best" lead system, 

 determined by comparison with the simplified (homo- 

 geneous) torso model and therefore having restricted 

 reliability only, seems to be a combination of elec- 

 trodes known as the SVEC system (standard vector 

 electrocardiogram) (431). 



The SVEC system in its best corrected form (called 



