lO QUATERCENTENARY STUDIES IN PATHOLOGY 



The question arises whether these irregular impulses originate from 

 the same point as those in the normal regular pulse, or whether the 

 irregularity of the discharge is due to the fact that some other point takes 

 up the function, and, being only imperfectly adapted to it, issues only 

 irregular impulses. The latter view has been suggested by Mackenzie,* 

 who holds that in certain forms of continued irregularity the ventricle, or 

 the auriculo-ventricular fibres, assume an automatic or endogenous 

 rhythm, while the auricle may assume the ventricular rhythm, or may 

 remain quiescent or "paralysed." Mackenzie supports this view by a 

 careful analysis of his tracings, and, in the particular cases observed, the 

 interpretation may be correct, although an alternative explanation might 

 possibly suffice without the necessity of adopting the inversion of the 

 cardiac rhythm postulated by him. But in animal experiments, in which 

 the ventricle has been induced to take up an endogenous rhythm by 

 means of drugs, no such irregularities of the heart rhythm are observed,-]- 

 and, in numerous unpublished experiments in which rapid induced 

 shocks were applied to the ventricle, one of us was able to invert the 

 cardiac rhythm, the ventricle giving the rhythm to the auricle, without 

 rendering the rhythm of either irregular after the first few seconds. An 

 endogenous ventricular rhythm may therefore be perfectly regular in the 

 mammalian heart, and it cannot be assumed per se to be the explanation 

 of irregularity in the tracings under discussion. 



In our tracings, then, there is nothing to suggest that the ventricle 

 originated the rhythm anywhere ; although we cannot exclude the 

 possibility of the whole phenomenon being due to endogenous ventri- 

 cular influence, it seems rather to have merely responded to the impulses 

 which it received at irregular intervals from the auricle. Not infrequently, 

 the impulses followed each other so rapidly that the ventricle could not 

 dilate sufficiently in the interval to permit of the entrance of blood from 

 the auricle. In other cases blood failed to enter in quantity, although 

 there seems to have been sufficient interval, and here the ventricular 

 contraction caused a very small pulse wave. 



The condition of the auricle and rhythmical area in the irregular 

 periods appears to have been one of extreme activity if, as we believe, 

 the rhythm in this case was given to the ventricle by some other part of 



* Study of the pulse ; BrzL Med. Journal, March 5th, 1904. 

 t Cushny. Jourtial of Physiology^ xxv. , p. 49. 



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