The spatial vectorcardiogram obtained by use of a trihedron and its scalar comparisons.

The spatial vectorcardiogram is supposed to represent the path of the cardiac vector viewed from a rather large distance. With this in mind, the authors propose a vectorcardiographic method based on a trirectangular trihedron. Comparisons are made between calculated scalar leads derived from the spatial vectorcardiogram, and real scalar leads recorded from the subject. In case of concordance the hypothesis of a single instantaneous cardiac vector within an homogeneous conducting medium is verified. This was found to hold for most circumstances. However, for those instances in which discrepancies arose another hypothesis is advanced. SPATIAL vectorcardiography intends to represent the variations of the instan-K_/ taneous cardiac vector as a function of time. This generally accepted definition implies the idea of an instantaneous resultant of all the elementary electrical sources of the heart. In principle such a resultant can be conceived or represented only if all electrical sources are viewed from a rather great distance, bearing in mind the volume occupied by the generator organ, the heart. Admitting that the vectorcardiogram which expresses the successive resultants can be obtained, the actual problem consists in knowing to what extent the successive fields corresponding to these resultants agree with the real electrical fields of the heart, as they are accessible on the human body in the form of multiple scalar tracings recorded at various points on the surface or even from the interior of the human body. In the attempt to resolve this problem, we started with the spatial vectorcardiographic tracing taken at a given distance from the heart and used a method of leading based on a trirectangular trihedron." 2 The latter is different from the trihedron previously proposed by Schellong.3 The actual research consisted in comparing 2 4-6 the scalar electrocardiograms derived from this vectorcardiogram and the real scalar electrocardiograms. This study necessitates certain remarks con-237 cerning the conducting medium of the body. Several opinions have been voiced on this subject of which two have claimed our attention, that of Wilson, on the one hand, and that of Burger on the other. Wilson,7-9 like Einthoven, accepted the simplified representation of instantaneous electrical cardiac sources in the form of a single dipole placed centrally or eccentrically within a sphere of homogeneous conductibility. He considered that this simplification took into account a certain number of observed facts with sufficient accuracy to explain the principles governing the distribution of potentials within the body. Nonetheless, Wilson, …