ELECTROCARDIOGRAPHY 



341 



OUCHOSAL "double- CUBE " WILSON TETRAHEDRON 



GRISHMAN CUBE 



FIG. 20. Illustrates the elect- 

 rode arrangements of three 

 commonly used systems. R, L, 

 and F in 5 are the standard 

 limb electrodes. The left and 

 right "cubic" systems are bi- 

 polar; the tetrahedron is a 

 unipolar system, where all deriva- 

 tions are recorded with the CT 

 as reference point. [From Frank 

 (198).] 



proximity potentials of 30 per cent and higher may 

 be found. This corresponds to the fact that calcula- 

 tions of the heart vector in a completely uncorrected 

 system are fairly reliable, the strictly precordial leads 

 excepted (118). A theoretical basis for the discrim- 

 ination of "heart vector" and "local" peculiarities 

 of unipolar leads will be given next. 



COMPARISON OF DIFFERENT TOTAL OR HEART VECTOR 



LEADS. The most important quality of a lead, for 

 clinical application, is its lead vector. Only such 

 leads as ha\e identical lead vectors can be regarded 

 as equal. A comparison between \arious systems (e.g., 

 of orthogonal character) is possible only if one knows 

 their lead vectors. Determinations of the lead vectors 

 of various electrode systems can be made only in torso 

 models. The results of such investigations show how 

 closely the various lead systems approach the ideal 

 (e.g., orthogonal) condition and to what extent the 

 results of such systems may be compared with each 

 other. In table i such a comparison is listed (428, 

 431). The result is that the S\'EC III system is by 

 far the most correct, both concerning lead vector di- 

 rections and standard deviations, which are mini- 

 mized by the corrections of this system. Comparisons 

 of various lead systems have often been made (80, 122, 

 144, 164, 168, 198, 207, 293, 308, 348, 368, 372, 400, 

 457, 460, 462). The results are too detailed to be re- 

 viewed here, but it is surprising to what extent deriva- 

 tions with comparable lead lines give similar results, 

 even when the electrode positions are rather different 

 (481). 



Local Leads. Theory of Unipolar Leads 



ELECTRODE SYSTEMS. A "local"' lead may be defined 

 as a lead, the lead field of which penetrates the heart 

 in an extremely divergent manner. For such leads, 

 the concept of a single uniform heart vector is not 

 applicable. They are used therefore with the intention 

 of recording electrical events in local areas of the 

 heart. There are two completely different methods of 

 recording local processes. First, the lead field of a 

 given lead selects the individual vectors of those fibers 

 which run in the direction of the field lines. Second, 

 a local lead close to the heart picks up the potential 

 of those parts of the heart which lie proximal to the 

 recording electrode ("proximity lead"). This happens 

 because the field lines of the lead field, in the case of 

 unipolar records from an infinite medium, are diver- 

 gent and penetrate every part of the field with a 

 density which is inversely proportional to the square 

 of the distance from the electrode (fig. 22). The mathe- 

 matical expression for this fact has been given in 

 equation 2.5. Unfortunately, in limited fields this 

 simple relationship is not valid. The invalidity may 

 be explained in a twofold manner. First, in a spherical 

 medium and with surface electrodes (fig. 23), the field 

 lines of the lead field are no longer straight lines; they 

 diverge in the complicated form indicated in figure 

 22. Second, the influence of the distance between elec- 

 trode and a local (individual) dipole is also compli- 

 cated. For eccentric dipole positions, the simple equa- 

 tions 3.5 and 3.6 are no longer valid, either. Math- 

 ematical treatment of eccentricity, which could lead 



