ELECTROCARDIOGRAPHY 



379 



(QRS) is a fairly staljle event and changeable only 



by strong influences on the propagation process, T is 



very sensitive to even slight changes in the metabolic 



equilibrium of the fiber, since the action potential 



(especially the plateau) is, in some respects, an 



indicator of metabolic normality. Unfortunately, the 

 — * 



"normal" values of G are still controversial. 



The magnitude of G in space has not been de- 

 termined with corrected leads, i^ut in a small group 

 of 18 young men (459). The area of Gs had an average 

 value of 97 ;uvsec in the corrected leads, with values 

 for QRSs of 43 and T, of 68 juvsec. The group tested 

 was too small for the establishment of satisfactory 

 standards, as the authors indicated, ijut the values 

 obtained do give some orientation. Much better 

 known are the magnitudes of the areas in the frontal 

 plane, of which Ashman made the first fundamental 

 measurements. He found that the normal average of 

 Gf is of the order of magnitude of 45 to 50 ^vsec, 

 depending largely upon the heart rate and diminishing 

 with its increase (86). Such standard values, however, 

 seem to be quite insufficient for the following reasons: 

 their magnitude depends so heavily on the size of 

 the QRS area that a linear relationship exists between 

 these two (fig. 62) (86, 216). Gf should be, according 

 to these observations with clinically normal persons, 

 about twice the magnitude of QRS (. The normal 

 values of Gf, that is, for individuals with normal 

 bodily performance, fall between the following 

 limits: Gf = 3 QRSf and Gf = 1.5 QRSf. The more 

 Gf is diminished below 1.5 QRSf, the higher is the 

 probability that the heart is abnormal. The more 

 pronounced the abnormality of the heart, as in 

 heart failure, the lower is Gf compared to QR.S f. 

 Unfortunately, we can never know the normal 

 QRSf value of a certain heart, if QRS is itself per- 

 ceivably distorted; which means, after all, that no 

 diagnosis about normality of G is possible in such 



cases. 



— > 



Though a correct analysis of T must include 

 calculation of G, an empirical judgment seems to be 

 possible, since the diagnostic classification into 



"normal" and "abnormal" T led to results com- 

 parable with those obtained by calculation of G and 

 a simple inspection of the EGG (432). But if the 



angle between G and QRS is somewhat borderline 

 at the upper limit, and if G is at the lower normal 



limit of its amplitude, the angle ijetween QRS and T 

 soon surpasses the value of 90°. In such cases, T may 



FIG. 62. Correlation between the Q.RS area and the ven- 

 tricular gradient in normal hearts, with all values taken from 

 the frontal plane projection. Nearly all values (7 exceptions) 

 lie in a "sector of normality" around a line giving the relation 

 G = 2 QRS. Lines II are the borderlines of the sector of 

 normality (G = 3 QRS and G = 1.5 QRS). Line I separates 

 the normal from the failing hearts. Line III gives the lowest 

 limit of normals in our series. [From Gartner & Schacfer 

 (216).] 



readily become negative in two standard leads 

 (II and III) without being necessarily abnormal. 



In normal hearts, the peak of T appears simul- 

 taneously in all heart vector leads. This necessarily 

 means that the vector loop of T appears as a straight 

 line. Only in abnormal cases does repolarization show 

 a phase shift in different leads, the T loop developing 

 an open, or even rounded, contour (283). 



The ST Interval 



As the EGG is the differential quotient of the 

 monophasic action potential of the cardiac fibers, a 



