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HANDBOOK OF PHYSIOLOGY >^ CIRCULATION I 



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FIG. 53. The potential distribution of the R, S, and T 

 deflections in the Wilson precordial leads V1-V4, in 100 normal 

 persons. [From Holzmann (34).] 



consider it more useful to give the vectorial data for 

 QRS. The total duration of QRS should not exceed 

 o. I sec in one of the leads. Yet it makes a difTerence 

 whether QRS shows a tall, narrow R with low but 

 broad Q or S waves, or whether the main deflection 

 is itself broadened. Only in the latter case could a 

 deviation from normal be assumed if borderline 

 values for the total duration are found. The duration 

 of QRS depends, as do all durations in the ECG, 

 upon the heart rate. Figure 54 gives the relationships. 

 These values are \'alid for the extremity lead with the 

 longest duration of the respective deflection. [For 

 details of the inajor literature see the textbook by 

 Lepeschkin (47). For the most important collections 

 of normal data see the following references (47, 79, 

 83. 154. 230, 246, 297, 350, 364, 448, 449).] A survey 

 of the most important electrocardiographic data is 

 given in table 4. 



Vectorial analysis of QRS can be properly done 

 only by recording the \'ector loop. Nevertheless, 

 many attempts are made to interpret conventional 

 ECG tracings as vectorial data. The simplest pro- 

 cedure is to estimate the sector in which the vector 

 of a deflection lies, by comparing the direction and 

 magnitude of this deflection in several different 

 leads (22 1, 540, 541). In some respects, the typological 

 index (see section 9) belongs among these methods. 

 If, however, more than one vector is determined, 

 the procedure is quite arbitrary. One could, of 



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FIG. 54. Relation between heart rate (abscissa) and dura- 

 tion of P, P-Q interval, and QRS. The upper curve represents 

 the upper normal limit of the P-Q interval, below this line the 

 average \alues in different age groups. Ordinate in '100 sec. 

 The data are based on a small series and may not be reliable. 

 [From Lepeschkin (46).] 



course, determine a vector of Q or of a small S. The 

 peaks of Q or S, however, are the random result of a 

 rotating heart vector, which projects itself on every 

 lead vector at a certain instance with a maximal 

 voltage. Such vectors Q or S are distinguished 

 from any vector position only by the choice of the 

 lead in which by chance the deflection appears to be 

 maximal. The range of the angles that such Q and 

 S vectors reveal is therefore very large (366) and 

 apparently without any physiological meaning. The 

 direction of the main deflection (R), however, shows 

 a very regular behavior. The axis of R or electrical 

 axis shows a migration with increase in age. In the 

 frontal projection, it migrates from a value (a) of 

 + 100° to +0° between birth and the age of 60 years. 

 In the horizontal plane, the direction of R migrates 

 from 50° to 130°, i.e., from an anterior to a posterior 



