294 



THE CIRCULATION OF THE BLOOD 



auricular flutter, however, on account of the extreme degree to which 

 the contractions of the auricles are increased, the ventricles are rarely 

 able to keep pace with the latter, so do not respond to every auricular 

 impulse. The failure of the ventricle is due partly to the refractory 

 phase of the conducting bundle and partly to the refractory phase of 

 the ventricular muscle itself. In some cases the ventricular response 

 fails at odd intervals only, but usually the missed beat recurs more 

 frequently. Two, three or even four auricular beats may occur before 



Fig. 103. Auricular flutter. In this case the ventricular rate varied from 82 to 98 per minute. 



(From E. P. Carter.) 



IvxMwMv.xl 



Fig. 104. Auricular flutter. Note the relative rates of A and V, and also that the ventricular 

 rate is regular. (From E. P. Carter.) 



one appears in the ventricle, so that the ratio between the beats of the 

 auricles and the ventricles may be 2:1, 3:1, or 4:1. In extreme cases 

 the two chambers may be completely dissociated, the auricle beating at 

 a rate of 300-400 per minute while the ventricle continues at its own 

 inherent rate of 35-40 beats per minute. 



Missed beats accompanying auricular flutter must not be confused 

 with true heart block; in this disorder the auricular beats are not 

 increased. 



Paroxysmal tachycardia and auricular flutter are each characterized 



