ELECTROCARDIOGRAPHY 



377 



FIG. 60. The image surface of fig. 16 is talcen to demonstrate 

 the lead vectors of Vi, Vo, and V3. An average horizontal 

 vector loop is shown, which projects on the Vi lead vector 

 mainly negatively. The inversion point of the projection in all 

 three leads is marked at the loop. In IV5, e.g., the loop begins 

 to project negatively in Vo. 



to the left. The image points of Vi and \''.>, however, 

 are .shifted far to the right, so that the loop projects 

 itself on the Vj lead vector mainly away from the 

 electrode and therefore shows an rS pattern, whereas 

 in V2 the first third of the loop projects in the positive 

 direction. Only V3 has a prevailing R. 



The vector loop may be transcribed into a two- 

 dimensional curve of usual type by recording the 

 magnitude of the spatial vector as ordinate against 

 time as abscissa. The curve thus registered resembles 

 fully a normal ECG. It has been described as "Abso- 

 lut-Ekg" by HoUmann, as "Manifest-Ekg" by several 

 authors (see 358). There is only limited information 

 incorporated in such curves. They nevertheless should 

 be included in any complete description of vectorial 

 data. 



I I . THE RS-T SEGMENT AND REPOLARIZATION 



The Normal T Wave and the I entiuular Gradient 



In the Einthoven standard derivations I, II, and 

 III, T is upright in the majorit)- of cases. Only Tm 

 is likely to be negative in normal hearts, if the ven- 

 tricular gradient is small or if the QRS axis is shifted 

 to the left. In such cases, the frontal vector of the 



gradient lies left of QRSj and the angle a of Tf is even 

 smaller than that of G. In the horizontal leads, 



especially in the Wilson precordial leads, T is upright 

 in nearly all leads and cases (fig. 53). This is mainly 

 due to the fact that QRS is negative in some pre- 

 cordial leads or exhibits at least a strong second 

 negative deflection (s), so that total eflfect is to shift 

 the T wave into the positive direction. The gradient, 

 in addition, strengthens this positive T wave, as the 

 gradient is directed from inward to outward, from 

 the back anteriorly, because the outer layers show 

 a much shorter plateau than the inner layers. The 

 epicardial and endocardial unipolar T is positive, 

 with gradients which (calculated from the figures) 

 seem to be small or (in the endocardial record) 

 zero'" (373). If parts of the myocardial wall are 

 cooled, the gradient and T are strongly influenced; 

 this needs no further explanation. Curiously enough, 

 T may be nearly normal in a heart showing no 

 visible movement (291). 



Vector analysis of T is restricted to study of the 

 areas of T, because G has a definite meaning only in 

 regard to areas. As a matter of fact, G is closely 

 correlated to the position of QRS. G is, in normal 

 cases, of much greater magnitude than QRS, so 

 that the resultant vector of T is bound to a position 

 forming relatively small angles between QRS and 

 T. As this angle reflects, in some respects, the relative 



magnitude of G as compared with QRS, it is of 

 definite clinical value. If in vector loops the axis is 

 determined as the line which bisects the planar 

 vector loop into two halves, the spatial angle be- 

 tween QRS and T is found for a corrected ortho- 

 gonal lead system to be, on the average, 56° ± 19° 

 with a range of 20° to 105° (93). With other lead 

 systems or with the null-contour method, the angles 

 appear to be considerably smaller and range between 

 43° (null contour), 18° (Grishman cube) and 28° 

 (Tetraeder) as their average values (252). No doubt 

 the frontal or horizontal plane projections of the 

 QRS and T axis form much smaller angles, they are 

 of the order of magnitude of 20° or less in the frontal 

 plane (19° ± 15° with the corrected orthogonal 

 system). If estimated from the plane projections, 

 large errors in the determination of the spatial angle 

 may occur (373). 



In tables 5 and 6 the values for QRS, T, or G have 



^^ In endocardial leads, QRS is nearly completely negative 

 (qS), and T therefore positive. It is unknown, however, why 

 the ventricular gradient appears to be zero. 



