Effect of Intracardiac Blood on the Spatial Vectorcardiogram

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 zvector 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 (Mlt M., and M8) 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-i to decrease to 33% and M2 to 40% of control values, but M8 rose to 125% of control values. These results are in accord with radial excitation for Mt and M2 and tangential excitation for M3. Decreases in hematocrit below control values caused opposite changes. Normal intracardiac blood causes an apparent increase of Mt by a factor of 3 and of M2 by 2.5 and a decrease in M3 of about 25%.