284 



THE CIRCULATION OF THE BLOOD 



Ventricular Hypertrophies and Defects of the Divisions of the 



A-V Bundle 



Hypertrophy of the right ventricle on account of the preponderance 

 of muscle on this side of the heart produces an electrocardiogram, in 

 which the right ventricular effects dominate the picture. Such a record 

 is characterized by a small R wave in lead I and a pronounced S deflec- 

 tion. In lead III the reverse obtains ; the R wave is high and S is dimin- 

 utive. In hypertrophy of the left ventricle the records are the opposite 

 of those just described. R is high in lead I while S is steep in lead III. 



Defects of the right or left branch of the A-V bundle give electrocardio- 

 grams which closely resemble those described as characteristic of left and 



Fig. 94-A. 



Fig. 94-B. 



Fig. 94-A. Electrocardiogram showing a lesion of the right branch of the conducting 

 bundle. Note that the T wave in this curve and in the succeeding one is opposite in direction 

 to that of the chief deflection (R or S) in the initial phase, and that the Q-R-S complex is 

 prolonged. (From E. P. Carter.) 



Fig. 94-B. Illustrating the effect upon the electrocardiogram of a defect of the left 

 division of the bundle. (From K. P. Carter.) 



right ventricular hypertrophy respectively. In the left branch defect 

 the electrical changes of the right ventricle will impress themselves upon 

 the electrocardiogram whilst in right branch defects the influence of 

 the left ventricle will prevail. The Q-R-S. complex which normally is 

 about l / w sec. in duration and is but little prolonged in the hypertrophies 

 is very noticeably lengthened in the bundle defects. (Figs. 94-A and 94-B.) 

 The T wave in the branch defects is opposite in direction to the chief 

 deflection of the Q-R-S. group. When R is prominent, T is inverted, 

 whereas when S is the chief deflection, T is upright. 



