378 HANDBOOK OF PHYSIOLOGY '■^ CIRCULATION I 



■*90 



0% 



ccQRS^ 



*20 + io +60 i-BO 



NORMAL HEARTS 

 ctG/^aRS, 



FIG. 61. Correlation between angle a of the QRS area and a of the ventricular gradient, taken 

 for the frontal plane. The large dots are the averages. The thick line represents the equation G = 

 0.72- aQRg + 10° and applies to normal subjects and to patients without clinical signs of failure. In 

 the left ventricular strain ("QRa negative) the correlation disappears almost completely. [From 

 Gartner & Schaefer (216).] 



been listed. Since the direction of Tin the frontal plane system: the positions are (after fig. 58) 131° for T 

 coincides rather closely with that of QRS, the vector 

 of the gradient coincides with the QRS vector as well 



in that plane. There is, however, a shift of the QRS — 



— > 



T angle in the course of age and with the direction 



of QRo. As figure 61 shows, the angle a of G is smaller 



than that of QRS in high values of the QRS angle 

 (right position type), but larger in small values of 



the QRS angle. Both coincide in their average value 

 at an Einthoven angle of approximately 36° (85, 216). 



In the sagittal plane, T coincides likewise fairly 



well with QRS, if measured with a tetrahedron or 

 determined by the null contour, but it shows a high 



deviation from QRS, if recorded with a corrected 



instead of 55° for QRo. T therefore is more anteriorly 



directed than QRo, which is, on the average, directed 

 somewhat toward the back (137, 368). The ventric- 

 ular gradient may be calculated by a vectorial 



addition, since G is the vectorial sum of QRS and T 

 (fig. 45). This means that the vector of the gradient 

 must lie between the vectors of QRS and. T Some 

 values for the direction of G are given in tables 5 and 

 6. Its frontal angle ot varies, according to different 

 authors, between 34° and 48° (85, 297, 459). The 

 horizontal (azimuthal) angle, not well known, is on 

 the average, 66° (459), measured as shown in figure 

 58. ^ 



The numerical \alue of G plays a decisive role in 

 the judgment of normality. \Vhereas depolarization 



