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HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



TABLE ifl. Lead Vectors of Common 

 Electrocardiographic Leads 



FIG. 21. The combination of electrodes for the sagittal 

 (Z — ) component of the ECG in the SVEC III system. Two 

 anterior and two posterior pairs of electrodes at the height of 

 the Ilird and IVth intercostal spaces at the sternum, and 

 with azimuthal angles of 30, 1 50, 2 1 o, and 330°, are combined 

 over the resistances indicated to a central anterior and a 

 central posterior point. This electrode combination is supposed 

 to have a nearly parallel and imiform lead field in the antero- 

 posterior direction and much resembles the derivation of 

 Reynolds et al. (382). 



to a correct description of the potential distribution 

 to local leads, is rather complicated (113, 195, 196, 

 250, 523) and must ht omitted here. It scarcely seems 

 applicable to analyses of human precordial or local 

 leads. 



There are several lead systems, the lead fields of 

 which reveal a certain local character of the lead. The 

 one most frequently used is the unipolar precordial 

 lead system. As shown in figure 23, the flow lines 

 penetrate the heart in a highly divergent manner, so 

 that parts nearest to the electrode show the higher 

 density of the flow lines when compared with the 

 more remote ones. There is, however, no sharp dis- 

 tinction possible between locally derived potentials 

 and those recorded with a minimal amplitude from 

 more remote areas. "Locally" and "generally" de- 

 rived potentials are simply idealized terms, meaning 

 that the nearer the part in question lies to the elec- 

 trode, the more its potential prevails in the total 

 pattern. 



The second system of more or less local character is 

 the "close bipolar system" using short distances be- 

 tween electrodes. Figure 24 indicates the lead field of 

 such electrodes as being strongly curved and showing 

 a considerable density at only short distances from the 

 surface. Yet we have no information as to how deep 

 a sufficiently dense part of the lead field penetrates into 

 the interior of the chest. Neither experiments nor cal- 

 culations are available. It isoijvious, however (fig. 24), 

 that even at a short distance from the electrodes the 

 field becomes quite uniform with nearly equidistant 

 flow lines, thoutjh these lines are still cur\'ed. The 



Azimuthal and elevational angles in the sense of fig. 58£). 

 With the key of these values, all records taken with these 

 leads can be used to determine the heart vector. [From 

 Schmitt (428).] 



T.\BLE I b. Lead Vectors oj Orthogonal Lead Systems* 



* See fig. 20. 



