ELECTROCARDIOGRAPHY 



353 



the heart. The interpretation of such records is rather 

 uncertain. In a recent paper by Torre.sani (67), the 

 results coincide much more with the behavior of the 

 dog heart : the latencies are minimal near the inter- 

 \entricular septal region, and the lateral parts of the 

 left ventricle are the latest activated. The book by 

 Groedel & Borchardt (30) does not include any 

 information on this, as the intrinsic deflections are 

 not visible in the records printed. Some papers of 

 Jouve et al. (278, 279), although they do not contain 

 an evaluation of latencies, do seem to indicate, as 

 far as the records can be read, that the shortest 

 latencies of the intrinsic deflection are found near 

 the pulmonary conus, and at least over the right 

 ventricle. Between dog and man no important diff"er- 

 ences in the surface and intramural potentials seem 

 to exist (277). Therefore we may draw our conclu- 

 sions from experiments on dogs and apply them to 

 the theory of the human EGG. 



Latencies Across the I'entricular Wall 



The behavior of superficial excitations can scarcely 

 explain the formation of the QRS complex. Although 

 Durrer (16) was seriously skeptical about our state- 

 ment, we still are convinced that the directions of the 

 epicardial excitation waves are a kind of indicator for 

 the propagation process within the musculature of the 

 ventricles, because we cannot imagine how, in a 

 geometrically reasonable way, excitation in the 

 ventricular wall could run in an essentially different 

 direction to the waves in the surface fibers. This 

 argument is fully corroborated by the result of intra- 

 mural derivations. Such derivations, however, have 

 been difficult to evaluate concerning their biological 

 reliability. The results presented by the laboratories 

 of Scher and Durrer (176-179, 414-420), however, 

 seem to indicate that the distortions are not too 

 serious. If a needle with multiple electrode points 

 along its axis is put through the heart, latencies may 

 be recorded either by taking bipolar records with 

 narrow electrode distances (176-179, 237, 414-420, 

 467, 468) or by using unquestionable intrinsic de- 

 flections in unipolar records (139, 321, 377, 397, 467, 

 468). The latter, however, may be recorded only 

 after some time of waiting, until the distortion by 

 the injury has disappeared. The results of both 

 methods are quite similar. They may be listed as 

 follows : 



/) The propagation of the excitation wave proceeds 

 in two directions: one (as in the classical concept) 

 from the endocardial to the epicardial surface; a 



/- 5 iDsec 



6- to msec 



11-15 msec 



16-20 msec 



FIG. 35. The latencies at the surface of the cat's heart. The 

 figures give the range of latencies in the area indicated, in 

 milliseconds. [Experiment of Harris (•237).] 



second one from a midpoint of the heart toward the 

 apex and the base, in two opposite wave fronts. 



2) The activation of the interventricular septum 

 is directed from apex to base (139, 468), with an 

 earlier activated point in the mid-anterior region 

 at the junction of the free wall and the .septum 

 (420). This fits optimally into the surface picture, 

 because this region lies directly below the "source" 

 region of figure 34. 



j) There is a minimal latency time in regions 

 lying in the wall, close to but not identical with the 

 endocardial layer. If we translate this latency picture 

 (fig. 36) into directions of the various excitation 

 wave fronts, we get a result like figure 37. However, 

 we should point to the fact that such translations 

 are always a bit questionable, since the excitation 

 process does not take the shortest distance between 

 the isochrones of figure 36. The only conclusion to 

 be drawn from these measurements is that there are 

 strong cancellation effects from excitation waves 

 traveling in opposite directions. 



./) If a needle electrode is put across the ventricular 

 wall, there is a "reversal" point where the polarity 

 of a bipolarly recorded potential is inverted (179) 

 and from which the excitation waves start in opposite 

 directions. 



5) On cross sections perpendicular to the heart's 

 axis, a similar conduction pattern can be seen: the 

 waves start at points quite near to the endocardial 

 surface, and spread radially in all directions (fig. 38) 

 (417-419). A tentative drawing of the directions in 

 which the excitation is conducted is given in figure 

 39. Activation of the septum is rather complicated, 

 as all authors agree. 



