ELECTROCARDIOGRAPHY 



Horizontal plane 

 seen as from nbcve 



375 



® 



-Q- 



elevational 



> 0°x 



Frontal plone 

 seen as from 



Ihe front 



az imjtha I 



® 



anterior 



® 



posterior 



ele vational 



—^ o°z 



Sogiriol plone 

 seen as from 

 the left 



'+ 



y 



aRs 



r 



FIG. 58. The axes and positions of angles in vectorial data, as used throughout this monograph. 

 A-C: the axes and angles in the projections on the 3 planes commonly used. D: the azimuthal (H) 

 and elevational (V) angles as coimted in a stereoscopic description. 



riorly. In the sagittal plane, viewed from the left, the 

 loop shows an initial deflection anteriorly and usually 

 superiorly, and then turns in a counterclockwise 

 direction inferiorly and posteriorly (422). In figure 

 59 some examples of normal loops are given. Rather 

 extreme types have been selected to show the range of 

 normality. The problem of describing the vector 

 loops in a manner that will permit easy standariza- 

 tion is by no means solved. The projections of the 

 spatial vector loop on the three conventional planes 

 in space are arbitrarily chosen, from the viewpoint of 

 biology. So the form of such loop projections can 

 scarcely be standardized in a reliable manner. The 

 best way to analyze the form of the loop and to 

 describe detailed information it contains would be to 

 determine angles of certain instantaneous vectors of 

 the loop, distinguishable from all other vector posi- 

 tions by some unmistakable characteristic. For- 

 tunately, such vectors can be defined in most cases. 

 Nearly every loop has an instant of maximum am- 

 plitude and the vector of this maximal voltage can be 

 regarded as the longitudinal axis which, however, 

 can be correctly defined only in a three-dimensional 

 model. If one can look at the loop broadside, the 



broadside width of the loop can be determined, being 

 defined as the greatest width of the loop perpendicular 

 to the longitudinal axis. The ratio of the width of the 

 loop to its length in the broadside view may be called 

 "openness," the average value of which ranges 

 between 0.5 and 0.6 (444). Unfortunately, not all 

 loops reveal a clear longitudinal axis. There are 

 round loops which display a circular outline regard- 

 less of their plane of projection. 



An often described peculiarity of normal QRS 

 loops is that they usually lie in a single plane. If, 

 therefore, the reference system of orthogonal elec- 

 trodes is rotated electronically, one finds certain 

 positions in which the loop will appear as a straight 

 line, the edgewise view of the loop's plane. If the 

 view is directed perpendicular to this plane, the loop 

 appears in its broadside view. This peculiarity allows 

 characterization of the loop in a relatively general 

 and simple way. We may, looking at the reference 

 system from the front, first rotate the system in either 

 direction around the y axis until the frontal projection 

 of the loop appears with its smallest view. By addi- 

 tional rotation of 90° in the positive direction, the 

 most open loop obtainable by azimuthal rotation 



