3o6 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



■0250 



FIG. 28. A scheme illustrating the direction taken by the 

 excitation wave on both sides of the heart as deduced by Lewis. 

 He considered (incorrectly) that the wave of excitation passed 

 down the muscle in the interventricular septum and then up 

 around the free walls. He also felt (correctly) that there was 

 inside-out spread of activity in the free walls and that the 

 septum was enveloped from both sides towards the center. 

 [From Lewis (71).] 



above. The discrepancy between the higliest figure 

 cited by one group (30 %) and the lowest cited by the 

 other (40%) for the amount of the septum excited 

 from the left seems small, and the major disagreement 

 concerns the question of a functional barrier to con- 

 duction in the septum. 



Details of Ventricular Excitation in Two 

 and Three Dimensions 



Using his plots of ventricular surface activation as 

 a rough guide and adding to them his demonstration 

 that there was a sizable Lnside-out component to 

 mural depolarization, Lewis deduced a two-dimen- 

 sional map of ventricular depolarization (fig. 28) 

 which greatly influenced later authorities and was 

 generally accepted (71). Lewis felt that the wave of 

 activity moved down the septum from the atrio- 

 ventricular junction, along the septal surface. He 

 thought that the Purkinje fibers then conducted the 

 activity upwards along the mural endocardium, so 

 that the basal portions of the free walls were the last 

 to be depolarized. In the illustrations he presented for 

 the dog, and in his deductions (based largely on the 

 dog) concerning the human heart, initial activity is 

 depicted as directed apically in the septum followed 

 by activity which moves basally in the walls. The 

 latest regions to be depolarized are in the lateral left 

 wall, which is depolarized later than the basal right 



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f:g. 29. A pattern of ventricular excitation as presented by 

 Sodi-Pallares. Note that the septum is shown depolarized from 

 left to right, although in the apical areas there is some move- 

 ment from right to left and from apex to base. Near the apex 

 of the free wall activity inovcs entirely from inside out. In the 

 lateral aspects of the left wall, and in most of the right wall, 

 activity moves from apex to base, as if there were some barrier 

 to movement from inside out. [From .Sodi-Pallares & Calder 

 (126).] 



Sodi-Pallares and collaborators (126) have pro- 

 duced a somewhat more detailed and somewhat 

 contradictory picture of two-dimensional ventricular 

 depolarization in the dog (fig. 29). Although they 

 do not state whether this picture results from de- 

 tailed measurements or from limited measurements 

 plus some deduction, it is probable that the material 

 is in part deduced. It should be noted that in figure 

 29 the septum is depolarized from left to right. The 

 free walls are generally depolarized in a fashion 

 similar to that which will be discussed in connection 

 with the studies by Scher cl al. (117, 119). It .should 

 however be noted that the basal cpicardial layers of 

 the wall are excited by a wave which mo\es up the 



