Radionuclide determination of right- and left-ventricular mixing

Previous models for the dynamics of the transit of the bolus of activity of labeled red cells through the chambers of the heart have assumed the complete and instantaneous mixing of tracer with the cardiac blood pool. This assumption can be conveniently tested with a radionuclide procedure. We present a model of the bolus transit through the right and left ventricle that allows the quantitation of the mixing of labeled cells with the residual blood of the cardiac chambers. This model was used to analyze the time-activity curves obtained from a variety of patients undergoing first-pass dynamic scans of the heart. It is shown that technetium-labeled red blood cells and technetium pertechnetate have indistinguishable mixing properties, and the blood in the left ventricle is more thoroughly mixed than that in the right ventricle.