Theoretical and experimental models demonstrate that intracavitary blood mass significantly alters the heart-lead relationship by augmenting normal and reducing tangential components of myocardial electromotive forces.
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 location. 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, especially the intracavitary blood mass, exert a powerful influence on the heart-lead relationship. The particular effect of the intracavitary phase is to augment the manifest strength of normal components 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 electrocardiograpic models. The net effect of the intracavitary phase is probably to produce quasi-vectorial registration of the electromotive forces of the heart, at least during the normal depolarization phase.
Daniel A. Brody (1956) studied this question.