THE PROBLEM OF IMPULSE CONDUCTION IN THE ATRIUM 127 



a£m (mV) 

 Is (/i Amps! 

 400 



Parallel to fibers 

 Perpendicular to fibers 



10 



•- ,- 



500 400 'iOO 200 100 fi 100 200 300 400 500 



Fig. 2. Spatial decrement of voltage. Abscissa, distance from current applying 

 electrode in micra; circular points, parallel to; square points perpendicular to 

 edge of trabecula (fiber direction). Ordinate, potential change per unit current 



in mV///A or kii. 



in a single experiment and from e.xperiment to experiment. Experiments were 

 done by placing the voltage electrode in surface cells at successively greater 

 distances along a single radius and then returning to the origin to check the 

 zero distance voltage change, if this value had changed appreciably the data 

 were rejected. It is our opinion that the results are a quite valid representation 

 of the electrical properties of the rat atrium. 



The significance of these results is quite clear. They make it likely that 

 activity spreads in the atrium by means of local circuit flow because de- 

 polarization of one cell produces appreciable changes in the potential of 

 adjacent cells. Strong confirmatory evidence for this view is the finding 

 (Draper and Mya-Tu, 1959; Sano et al., 1959) that conduction velocity is 

 several times faster in the fiber direction than perpendicular to it. This be- 

 havior is directly predicted from the observed non-uniform spread of electro- 

 tonus. Experiments on the same principle as those Hodgkin (1937) conducted 

 on nerve nearly twenty-five years ago would be required to prove that local 

 circuits are the means of propagation. However, we have clearly established 

 the possible existence of this mechanism, and there seems little point in 

 postulating a more complicated means of intercellular transmission unless 

 compelling evidence is adduced. Sperelakis, Hoshiko and their co-workers 

 (Sperelakis et al., 1960a, b) have recently contended that the transmission of 

 impulses in the heart is not electrical but by a more complicated, relatively 



