280 



THE CIRCULATION OF THE BLOOD 



radial pulse may be regular or irregular. The cause for the failure of 

 every auricular beat to travel to the ventricle during auricular flutter 

 is partly the refractory condition of the bundle, and partly the refrac- 

 tory phase of ventricular contraction. The bundle may be considered 

 as a narrow bridge which will transmit the impulses across it only at a 

 certain rate. If the impulses arrive too rapidly, only some of them can 

 cross the bridge, and even of those that do cross, a limited number only 

 will find the ventricle in a condition of excitability because of the re- 

 fractory period (see page 178). Tracings showing auricular flutter are 



L^a 



U Kv k I sr Iw 



v 



Fig. 105. Auricular fibrillation. Note the absence of all "a" waves from the jugular tracing, the 

 marked irregularity of the radial pulse, and the occurrence of "c" and "v" during the sphygmic 

 period. (From E. P. Carter.) 



given in Figs. 103 and 104. In one of them the radial pulse is regular; 

 in the other, irregular. 



Auricular Fibrillation. The contractions of the auricle, as already ex- 

 plained, are entirely irregular, so that the jugular tracings show an en- 

 tire absence of all "a" waves, the radial tracing being characterized by 

 the complete absence of a dominant rhythm and by great variation in the 

 length of the individual beats from one cardiac cycle to the next. This 

 irregularity does not repeat itself, and the long pauses are not simple 

 multiples of the shortest pause. Tracings from a case of auricular 

 fibrillation are shown in Fig. 105. 



