276 THE CIRCULATION OF THE BLOOD 



these curves and their time relations to one another and to the normal 

 electrocardiogram, it is necessary to obtain a curve which may serve 

 as a standard. This is provided for by leading from a series of contacts 

 placed directly upon the endocardium or the surface of the heart. When a 

 levocardiogram, a dextrocardiogram and a biocardiogram are charted (Fig. 

 84-C) with their voltages along the ordinates and their respective time 

 phases in the same vertical line, it will be found that in lead I the record 

 of the left ventricle shows a pronounced R wave and a diminutive S. 

 The dextrocardiogram on the other hand shows a marked S wave and a 

 stunted R deflection. The height and consequently the potential value of 

 each wave of the bicardiogram was found to represent the algebraic sum of 

 the potential values of the corresponding waves in the dextrocardiogram 

 and the levocardiogram. When the three records were taken in the 

 other leads and charted as described the same relationships were found 

 to exist. The rotation of the electrical axes in the two ventricles (cf. 

 Fig. 84-0) furnishes us with an explanation for the variations in the 

 potential values recorded respectively from the two chambers in a com- 

 mon lead and from a given chamber in different leads. . 



The right and left ventricles in the other leads when charted as de- 

 scribed also show differences in their potential values during identical 

 time phases. Thus, in the case of the levocardiogram taken in leads II 

 and III, a well marked depression S is seen but R is of low value. In 

 the case of the dextrocardiogram R is high in these leads but S is absent. 

 The bicardiogram in either the second or third lead, as in the case 

 of the first lead represents the algebraic sum of the records obtained 

 from the individual chambers in the corresponding lead. 



As a result of these researches it is believed that the Q.R.S. complex in 

 the physiological electrocardiogram is a composite picture consisting of 

 the algebraic summation of the electrical effects in the two ventricles. 

 The Q wave is produced during the spread of the excitation wave in the 

 septum and is a left sided effect in lead I and a right sided effect in 

 leads II and III. The beginning of the R wave is produced by the spread 

 of the excitation wave in both ventricles. The remainder of the R wave 

 is a left sided effect in lead I and a right sided effect in leads II and III. The 

 S wave is a right sided effect in lead I but a left sided effect in the other 

 leads. Such a conception of the manner of production of the initial phase 

 (Q. R. and S. deflections) of the ventricular complex renders the analysis 

 of certain clinical curves, notably those associated with the hypertro- 

 phies and bundle branch defects, a less difficult matter (see page 284). 



The short period between the S and T waves during which the electro- 

 cardiogram follows the base line indicates that the whole heart is in the 

 excited state and, in consequence, a condition of perfect potential bal- 

 ance exists between its different parts. 



