Effect of hematocrit on electrocardiographic potentials and dipole moment of the pig

The Brody hypothesis posits that blood in the heart chambers enhances body surface potentials due to radially oriented excitation and diminishes those due to tangentially oriented excitation. Evidence supporting the hypothesis has been found in models and in dogs. The current study was performed in pigs (Sus scrofa), anesthetized with sodium pentobarbital, to determine whether the phenomenon could also be demonstrated in a species having a ventricular activation pattern distinctly different from that of dogs. Hematocrit was varied from normal 35.3 +/- 1.1% to as low as 19.8% by hemodilution and to as high as 68.0% by hemoconcentration. Surface potentials early in QRS increased and those late in QRS decreased in hemodilution experiments, while the reverse was true in hemoconcentration experiments. Total QRS duration was 38.0 +/- 0.8 ms. The first peak in resultant dipole moment magnitude, at 5.4 +/- 0.2 ms, was inversely related to blood resistivity with a linear regression correlation coefficient r = -0.76; the second peak, at 10.9 +/- 0.1 ms, was directly related, r = 0.52; and the third peak, at 17.5 +/- 0.2 ms, was directly related, r = 0.89. When interpreted in accordance with the Brody hypothesis, changes in body surface potentials and in resultant dipole moment were consistent with radial excitation of the apical septum, ill-defined orientation of free ventricular wall excitation, and tangential excitation of basal left ventricle and septum.