Effects of intracardiac blood volume changes on the electrocardiogram

Effects of changes of intracardiac blood volume were studied using a simple model consisting of a circle of resistivity 150 ohm-cm (representing the blood filled cavity) immersed in an infinite two-dimensional medium of resistivity 400 ohm-cm (representing the myocardium and external medium). For each case, potentials due to an artificial dipole just outside the circle were computed. Both radial and tangential dipoles were used. The area of the circle was changed to simulate blood volume changes. At remote points, the results agreed with the Brody theory in that potentials due to tangential dipoles were decreased and potentials due to radial dipoles were increased. On the circle (representing the endocardium), however, potentials were decreased for both radial and tangential dipoles in the vicinity of the dipole. All effects were enhanced by increasing the area of the circle. As area increased, radial dipoles appeared to be located more centrically, but tangential dipoles appeared to be located farther away, relative to true dipole location. Possible reasons for conflicting results on the effects of intracardiac blood volume changes on the electrocardiogram were examined and suggestions made for reduction of errors.