A Theoretical Analysis of Intracavitary Blood Mass Influence on the Heart-Lead Relationship

As a result of theoretic advances made during the past 10 years, it is now feasible to record scalar and vector electrocardiograms in a manner which is independent of body shape and cardiac loca-tion. A similar independence of the body's electric inhomogeneities has not yet been achieved. On the contrary, the evidence presented here shows that inhomogeneity phases in the body, espe-cially the intracavitary blood mass, exert a powerful influence on the heart-lead relationship. The particular effect of the intmeavitary phase is to augment the manifest strength of normal eompo-ncnts of myocardial doublets, and to reduce the manifest strength of tangential components. This augmentation-reduction effect is quantitatively predictable under conditions of simple idealization, and has been confirmed by experiments on electrocardiographic models. The net effect of the intra-cavitary phase is probably to produce quasi-vectorial registration of the electromotive forces of the heart, at least during the normal depolarization phase. THE role of the body's electric in-homogeneities in both theoretic andpractical electrocardiograph} ' has not yet been clearly denned. Most of the recent reports on the heart-lead relationship either neglect inhomogeneity entirely, or else tend to show that the relationship is not materially affected by the presence of inhomogeneities. The experimental results which fall in the latter cagegory may be summarized as follows: (1) the Burger triangles of a homogeneous two-dimensional model did not differ greatly from those of electrically inhomogeneous models of the same external configuration,1 (2) the scalene tetrahedron determined upon an electrically homogeneous, three-dimensional phantom2 was essentially the same as that determined upon a similar, but electrically inhomogeneous, model, ' (3) the dipole moment determined from the surface potentials of electrolytic tank models was essentially the same whether the models were electrically homogeneous or inhomogeneous,' ' (4) the surface isopotential traces of a lead field wer