304 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



meters per second Ijeing commonly found . . . the 

 impulse travels through the outer or sub-epicardial 

 third of the wall at speeds of only 300 to 400 mm per 

 second (126)," 



He further feels that the apical portions of the 

 free wall are activated earlier than tlie basal portions 



PULMONAR'r CUSPS 



ANTERIOR 

 PAPILUARV jiy 

 MUSCLE 



Jif«J0O2O - 02 5 

 i3i3o026 - 030 

 030 ■ 035 



[7^0035 -CCfO 



FIG. 25. Activation of the right surface of the interventricular 

 septum recorded by Sodi-Pallares. Earliest activity was re- 

 corded near the base of the anterior papillary muscle, from 

 this region the activity spread radially towards the lateral, 

 inferior, and superior borders of the septum. [From Sodi- 

 Pallares & Calder (126).] 



(fig. 21) and thinks that the subendocardial layers are 

 depolarized in such a fashion that they give rise to no 

 potentials in leads outside the region. This idea has 

 also been strongly advanced by Prinzmetal a:id 

 colleagues (89). Sodi-Pallares feels that, because of 

 Purkinje penetration into the wall, a number of 

 closed volumes of inuscle are activated from Purkinje 

 strands. Since these are closed volumes, they give 

 ri,se to no potentials in external leads. 



The question of Purkinje penetration has ramifica- 

 tions beyond the electrophysiological and anatomical. 

 It has been claimed that, because of Purkinje pene- 

 tration, only the outermost ventricular layers con- 

 tribute to the normal QRS complex and therefore 

 that lesions of most of the inner wall will be unde- 

 tectable electrocardiographically. 



The work of Prinzmetal and his colleagues deserves 

 some comment. All of the early papers in a very 

 large series stressed the fact that most of the inner 

 layers of the wall were silent and were depolarized 

 before the beginning of the peripheral electrocardio- 

 gram. The faulty reasoning on which this claim was 

 based has been analyzed in exienso (119). A final 

 paper in the series (85) re-examined the major claim 

 (excitation of inner layers before the beginning of 

 QRS) and found it to be incorrect. In the various 

 papers from this laboratory between 33}--^ and 80 per 

 cent of the wall was considered to be siinultaneously 

 activated. 



In the hearts of ungulates, where penetration of 

 Purkinje fibers can be clearly shown histologically, 

 the excitation of the wall is quite different from mural 

 activation in tiie clog. As has been shown by Hamlin 

 & Scher (51) in the goat, tlie direction of activation 



FIG. 26. Simultaneous oscillographic records from multipolar electrode across apical septum 

 (1-14). Negative potentials gave downward deflection. Unipolar records on left; bipolar on right. 

 Channel 15, fixed time reference; channel 16, lead II ECG. Time pips are 5 msec apart. Potentials 

 on the fust 14 channels of unipolar records average 40 mv. Bipolar records show diflTerence between 

 adjacent unipolars (one minus two, etc.). Activity proceeds from both endocardial surfaces toward 

 center of septum. [From Scher el al. (121).] 



