CLINICAL APPLICATIONS OF ELECTROCARDIOGRAPHS 



283 



beat." The electrocardiogram records a P deflection but no ventricular 

 complex, showing that the auricles have contracted at their usual rate 

 but that the ventricles failed to respond to the stimulus coming from 

 the sinoauricular node (Fig. 93). 



COMPLETE DISSOCIATION. In a simple case of complete dissociation 



t /! -T 



Fig. 93. Partial dissociation. Note the failure of ventricular response following the second P, 

 which has been preceded by two extrasystoles (x) of ventricular origin. 



the auricles beat independently of the ventricles; hence the P deflection 

 of the electrocardiograms bears no relation to the ventricular complex 

 (Q-R-S-T) (Fig. 94). The P deflections space regularly and are easily 

 made out when they fall during diastole of the ventricle. Occasionally 

 the auricle will happen to contract during ventricular systole, causing a 

 iistortion of the ventricular complex by the super-imposition of a P 



Fig. 94. Complete dissociation. Note that the P wave spaces regularly and bears no definite re 

 lation to the R wave of the ventricular complex. Auricular rate 72. Ventricular rate 40. 



deflection. Except when this occurs the Q-R-S-T complex is the normal 

 supraventricular type. The P deflections occur more frequently than 

 the Q-R-S-T complex, showing that the auricles are beating more often 

 than the ventricles. The auricular rate in the average case of complete 

 heart -block is about 72, while the ventricular rate is much slower (35 to 40). 



