Effect of ventricular end-diastolic volume on vectorcardiographic potentials of the pig

The Brody hypothesis proposes that alterations in end-diastolic blood volume will produce changes in the magnitude of cardiac electrical potentials recorded at the body surface. To test this hypothesis, several procedures that affect end-diastolic volume were applied in 28 anesthetized domestic piglets. The pig dipole moment magnitude curve is typified by two peaks, designated M2 and M3, which responded to these procedures. Doubling heart rate by electrical pacing or hemorrhage of 20 ml/kg produced reduction in M2 by 30% and 29%, respectively. M3 rose by 27% and 29%, respectively, under these two conditions. Reduction of end-diastolic volume by partial occlusion of the vena cava produced similar effects. Maneuvers increasing end-diastolic volume produced directionally opposite effects. Temporary aortic coarctation of phenylephrine injection caused an increase in M2 with no change in M3, accompanied an acute elevation of arterial pressure. Thus, the pig electrocardiogram shows changes, attributable to adjustments in end-diastolic volume, consistent with the Brody hypothesis, suggesting potentials for this technique in monitoring changes in end-diastolic volume.