334 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



FIG. 13. Construction (pre- 

 diction) of precordial records 

 from a vector loop recorded with 

 the rectangular bipolar electrode 

 system of fig. 20 (Duchosal 

 cube). Both the constructed 

 and the actually recorded trac- 

 ings are given. Left ventricular 

 hypertrophy of a man, 65 years 

 old. To the upper left the 

 standard ECG. [From Duchosal 

 & Sulzer (i.'j).l 



itself on the lead line of a derivation and how this line 

 can be determined. 



The Single Dipole Concept of the Electrocardiogram 



There is nearly complete agreement that the single 

 fiber may be regarded as a dipole. But it is very un- 

 certain how far the superposition of all simultaneously 

 generated fields of the various fibers may be regarded 

 as the field of one single resultant dipole, which may 

 be represented by one resultant vector. It must be 

 decided whether such a single dipole concept is 

 valid for all possible derivations or for special elec- 

 trode arrangements only. Many attempts have been 

 made to prove the general correctness of this assump- 

 tion. In 1949, Duchosal & Sulzer (15) started an 

 investigation in which the form of a record taken with 

 precordial unipolar leads was predicted from a 

 vector loop recorded with a rectangular bipolar 

 electrode system, the electrodes of which were rela- 

 tively far away from the heart (fig. 13). In the report 

 of this investigation it has been stated that unipolar 

 electrodes situated in a circle around the thorax, at the 

 height of the heart mass center, tended to find "mirror 

 patterns" with certain electrode positions, the con- 

 nection of which went in most cases through the 

 heart center (fig. 14). This result is one of the most 



frequently cited tests for the single dipole concept. 

 If a single vector of fi.xed location exists, it really 

 should be expected that for each electrode position 

 used a second one may be found with the same form 

 but opposite polarity of the ECG. This is identical 

 with the possibility of finding two electrode positions, 

 the lead vectors of which lie in a strictly opposite 

 direction (fig. 15). The mirror pattern technique has 

 been repeated se\eral times by various authors and 

 with similar results (130, 200, 320, 352, 430, 461). 

 The best generally valid method to determine mirror 

 patterns has been described by Frank (199). 



Though mirror patterns do exist, and cancellations 

 are possible, it can scarcely be doubted that the 

 dimensions of the heart are great compared with the 

 dimensions of the thoracic field. It was claimed at a 

 very early stage in electrocardiographic research that, 

 from precordial electrodes, a "partial derivation," 

 or partial ECG, can be recorded (29). This should be 

 expected from the fact that, viewed from a precordial 

 electrode, fibers in the remote parts of the heart 

 appear under a much smaller solid angle than those 

 in the proximal parts. The latter therefore prevail 

 in the record [nondipolar fraction (130) or proximity 

 potentials]. We should mention, however, that in 

 Frank's opinion (203) even the strictly precordial 

 electrodes do not show peculiarities in the form of 



