Assessment of severity of tricuspid regurgitation by analog computer analysis of dilution curves recorded by scintillation camera.

To estimate the severity of tricuspid regurgitation, we developed a new mathematical model of the circulatory system, in which the right atrium and the right ventricle were represented by a single mixing chamber and tricuspid regurgitation was expressed as a reverse flow from the right ventricle to the right atrium with a time delay equivalent to one cardiac cycle. The actual dilution curves obtained from the right atrium and the right ventricle following rapid intravenous injection of Technetium-99m-macroaggregated human albumin were fitted to the theoretical curves based on the above-described model. The use of macroaggregated albumin avoided the contamination of the dilution curves by radio-activity from the left heart or by the recirculation of the tracer due to left to right shunt. Mean transit times and percentage of regurgitation, as given by the ratio of regurgitant flow to total outflow from the right ventricle, were determined by an analog computer. The correlations of these results with the findings of other examinations, including contrast echocardiography, demonstrated that the present method may be useful in detecting tricuspid regurgitation and in grading its severity.