ELECTROCARDIOGRAPH'!- 



373 



FIG. 57. Method of recording vectorcardiograms. The 

 potential differences of two orthogonal lead systems are led 

 to a cathode-ray oscilloscope in the manner indicated, so 

 that the spot of the oscilloscope is shifted into a position de- 

 termined by the vectorial addition of the two lead voltages, 

 both regarded as \ectors lying in the direction of their lead 

 lines. (From Schellong (59).] 



of rotation (clockwise, counterclockwise). This is 

 done by giving timing signals of asymmetrical wave 

 form (521). Special techniques have been developed 

 to separate the loops of the P, QRS, and T waves 

 of the EGG (243). 



Description of vectors requires that conventions be 

 established regarding the side from which the loops 

 are viewed. This notation has been given in section 6. 

 Tabulated functions are available (231) for conversion 

 of angles from plane projections into their spatial 

 values. The different lead systems of course offer 

 considerable differences in angles and amplitudes. 

 This has been discussed in section 6. For some detail 

 see table i and the paper by Pipberger (369). A 

 good and simple electrode combination has been 

 given by Frank (202). One may find even such 

 simple triaxial electrode combinations as V2 (for z), 

 Vg (for x), and VF for the y axis (90) or of the Eint- 

 hoven frontal plane derivations in comparison with a 

 back electrode (201). In these lead combinations, the 

 location of the dipole has considerable influence on 

 the correctness of the vector analysis (201). Such 

 errors arising from this variable can be theoretically 

 corrected only in torso models; nevertheless, they are 

 of little clinical concern since "normal" limits are 

 not very well defined. 



The spatial analysis of the vector is doubtless of 

 great importance. The frontal plane projection alone 

 contains too little information, even in respect to 

 amplitudes. Many hearts show low voltages in the 



frontal plane leads, and normal voltages in the sagittal 

 direction. Spatial vector positions, moreover, are 

 extremely valuable for interpreting excitation pro- 

 cesses, local hypertrophies, etc., so that a spatial, 

 three-dimensional representation of electrocardio- 

 graphic data is indispensable. The spatial orientation 

 can be derived from two-plane projections. The 

 difficulties in presenting a plastic picture of these 

 orientations, nevertheless, are great. It is therefore 

 advantageous to view this orientation in a stereo- 

 scopic device (45a, 59, 97, 427). 



The stereoscopic presentation of \ectorial data is, 

 by virtue of its technical procedure, a subjective one. 

 If an objective analysis of the stereoscopic data is to 

 be made, the projections on the three planes of space 

 must be described, and there is a convenient method 

 for such a description, using electronic resolvers. 

 Such a system is fed through the voltages of an ortho- 

 gonal lead system (i.e., a system with lead vectors of 

 equal length and a strictly orthogonal orientation). 

 The voltages are electronically mixed, in such a 

 manner that the lead system is virtually rotated 

 around its three axes. By such a rotating procedure 

 it is possible to determine the position of the system 

 in which the axis of a given complex (P, QRS, T) 

 appears minimal, so that the observer seems to look 

 at the peak of the axis from a point in line with its 

 direction. The rotation angle can be read directly 

 from calibrated dials (127, 132, 375, 427). Electronic 

 computers can record directh' the angles of the 

 momentary vector position (339). 



THE NORMAL QRS VECTOR LOOP. The QRS loop in 



most cases shows a distinct longitudinal axis which 

 forms certain angles with the orthogonal axes of the 

 lead system. Various authors give rather different 

 figures for the mean values of these angles (79, 137, 

 246, 366, 368, 446, 453, 498, 500, 537). Some results 

 are listed in tables 7, 8, and 9. The longitudinal axis 

 lies in the frontal and sagittal plane between 35° and 

 75° (reckoned in the manner of fig. 58) and in the 

 horizontal plane between the limits of iio and 140°. 

 The angles vary with age, showing a trend to di- 

 minish in all planes. In this respect, they resemble 

 the angles of the R deflection (498). 



The sense of rotation of QRS in normal adults in 

 the frontal plane depends on the axis of the loop: 

 those with low values of a usually rotate counter- 

 clockwise, whereas the rest usually rotate clockwise. 

 In the horizontal plane, the loop is characterized by 

 an initial anterior deflection, and is then inscribed in 

 a counterclockwise direction, to the left and poste- 



