CHAPTER XXX 



CLINICAL APPLICATIONS OF CERTAIN PHYSIOLOGICAL 



METHODS (Cont'd) 



CLINICAL APPLICATIONS OF ELECTROCARDIOGRAPHY 



The Electrocardiogram in the More Usual Forms of Cardiac 



Irregularities 



By R. W. Scott 



The principle of the application of the string galvanometer to the 

 study of cardiac irregularities has been indicated. It is our object here 

 to outline some of the more common forms of irregular heart action, 

 with a brief description of the abnormalities in the electrocardiogram 

 resulting therefrom. For the sake of comparison a normal electrocar- 

 diogram is shown in Fig. 82. The cause and relationship of the various 

 deflections have been explained (see page 262). 



Sinus Arrhythmia. — This irregularity is seen commonly in children 

 and young adults, and is without pathologic significance. The electro- 

 cardiogram presents the normal deflections and shows by the varying 

 spaces between the P deflections that the cardiac impulse has been gen- 

 erated at slightly irregular intervals. 



Sinus Bradycardia. — The electrocardiogram in a simple case of sinus 

 bradycardia is usually normal, except that the deflections occur at an 

 unusually slow rate (Fig. 85). This indicates that the cardiac impulse 

 is built up at a slow rate, but when generated it evokes a normal auric- 

 ular and ventricular contraction. 



The Extrasystole. — The extrasystole may be either auricular or ven- 

 tricular in origin. Occasionally a rare type is seen in which the im- 

 pulse arises in the junctional tissues between the auricle and ventricle. 

 When the focus of impulse production is at or near the sinoauricular 

 node, the resulting electrocardiogram complexes are practically normal. 

 If, however, the seat of impulse formation is removed from the S-A 

 node, the P deflection may be distorted or actually inverted, followed 

 by a normal Q-R-S-T complex (Fig. 86). 



In the case of ventricular extrasystole, the cardiac impulse originates 

 in either the right or the left ventricle. This abnormal site, together 



2GG 



