Effect of Intracardiac Blood on the Spatial Vectorcardiogram

Abstract

Studies were done on dogs in vivo to determine the effect of intracardiac blood on the electrocardiogram. By exchange transfusions of packed cells or of Rheomacrodex, hematocrit was raised to over 70% or lowered to 16%. The electrical resistivity of the blood changed accordingly from control values of 150 ohm-cm to over 500 ohm-cm or to as low as 67 ohm-cm. The x-, y-, and z- vector leads were processed by analog computer. Computer output signals were: spatial dipole moment, M, vertical angle, V°, and horizontal angle, H°. Three peaks of M (M 1 ; M 2 , and M 3 ) were found at mean times of 29%, 42%, and 64% of QRS duration. Increases in blood resistivity to values near that of the myocardium caused M 1 to decrease to 33% and M 2 to 40% of control values, but M 3 rose to 125% of control values. These results are in accord with radial excitation for M 1 and M 2 and tangential excitation for M 3 . Decreases in hematocrit below control values caused opposite changes. Normal intracardiac blood causes an apparent increase of M 1 by a factor of 3 and of M 2 by 2.5 and a decrease in M 3 of about 25%.