ELECTROCARDIOGRAPHY 



343 



FIG. 22. Lead field of a unipolar electrode in a homogeneous 

 field, of "local" character, as far as events in the neighborhood 

 of such electrodes are concerned. The "different" unipolar 

 electrode lies in an infinite homogeneous medium, the field 

 lines of its lead field diverging symmetrically into all directions; 

 the "indifferent" electrode may be regarded as infinitely 

 remote. The potentials recorded from three membranes Qi, 

 Q.,, and Q3 are inversely proportional to the square of the 

 distance (and proportional to the number of flow lines pene- 

 trating the acti\e cross section of these sources). 



F!G. 23. Lead field of a unipolar chest electrode, i.e., from 

 an electrode on the surface of the field. The flow lines are 

 strongly curved and the relation between recorded potential 

 and square of distance of fig. 22 is no longer generally valid. 

 The flow lines of the lead field have been produced in a fluid 

 model by streaming stained fluid entering the field through 

 the electrode point ("fluid mapper"). [From McFee & Johnston 

 (34O.] 



closer the electrodes lie together, the greater difference 

 exists between lead field densities in neighboring and 

 remote parts of the heart. The potential differences 

 recorded are very low with short electrode gaps and 

 may even be so small that such electrodes do not yield 

 sufficient input to the ordinary ECG amplifiers, even 

 though they lie very near the heart's surface. 



Records from close bipolar electrodes have no 

 essentially different features : for example, the QRS 

 complexes have nearly the same durations as in total 

 leads. The proximity features of the record, never- 

 theless, are remarkable. There are some peculiarities 

 of the records which cannot be explained by the 

 single dipole assumption (98, 405). Thus, the latency 

 of the peaks of Q, R, and S, respectively, behave 

 differently from what would be expected of a rotating 



FIG. 24. Lead field (schematically drawn) of a close bipolar 

 lead. The field lines show a considerable density only near the 

 electrodes. At greater distances, the lines become less curved 

 and more nearly uniform; and their direction, where they 

 penetrate the heart, is approximately parallel to the line 

 connecting the electrodes, at least for the greater part of their 

 flow. 



POINT OF REVERSAL 

 \ 



FIG. 25. Tracings from close bipolar chest leads (distance 3 

 cm), with horizontal electrode positions varying from the 

 right margin of the heart (no. 2) to the left (no. 7). The records 

 are taken thus: the electrode pair is shifted 3 cm toward the 

 left side of the chest between each tracing. With each move, 

 the right electrode (as viewed from the subject; is placed 

 where the left member of the pair had previously been. Between 

 4 and 5 ( appro.ximately over the heart center), the main 

 deflection is re\ersed. P is omitted in all records. The QRS 

 duration is nearly the same as in the standard leads. [So-called 

 "Herzbild" of Ernsthausen & Kienle (18).] 



dipole. The main deflection (R) of the records is 

 inverted, if the bipolar leads are moved from left to 

 right or from above downward to a certain line 

 (fig. 25). Interpretation of this behavior has been 

 attempted on the assumption that excitation waves, 

 starting in the center of the heart and running in 

 divergent directions, build up these local fields with 

 their opposite potential gradients (18). However, 

 this interpretation can scarcely be adopted in this 

 general formulation. 



Another system has been described by Fattorusso 

 et al. (191) and Thaon et al. (482) consisting of 

 "concentric" electrodes (a ring-shaped indifferent 

 with a centered recording electrode). The lead field 



