Mitral regurgitation determined by radionuclide cardiography: dependence on posture and exercise.

OBJECTIVES To evaluate dependence of posture and exercise on the degree of mitral regurgitation using combined first pass and equilibrium radionuclide cardiography. DESIGN 24 patients with clinically stable chronic mitral regurgitation and sinus rhythm were studied by first pass list mode and simultaneous multigated frame mode equilibrium radionuclide cardiography using red cells labelled with technetium-99m. RESULTS When patients changed posture from supine to sitting upright, left ventricular volumes decreased considerably. Regurgitation tended to increase in patients with valve prolapse but decreased in patients with ischaemic heart disease and dilated cardiomyopathy. During submaximal bicycle exercise cardiac output increased without dilatation of the left ventricle. The increase in left ventricular forward stroke volume was more pronounced than that in the total stroke volume, leading to a considerable decrease in the regurgitant flow through the mitral valve. The repeatability and observer variability of radionuclide determination of regurgitation was acceptable, with limits of agreement within about 10%. CONCLUSIONS Change in posture induces a normal haemodynamic response in most patients with chronic mitral regurgitation; the effect of posture on regurgitation depends on the underlying disease. Mild to moderate exercise causes no deterioration in the severity of regurgitation.