Quantification of mitral insufficiency by radionuclide techniques.

Radionuclide imaging is useful in the assessment of left and right ventricular function in patients with a variety of cardiac diseases. Measurements of particular interest in patients with mitral insufficiency concern the left ventricle: ejection fraction, end-systolic volume, end-systolic volume/end-systolic pressure ratio, and the right ventricle (mainly its ejection fraction). The ejection and filling parameters of the left ventricle as well as parameters of the left atrial volume curve can also be of interest. Quantification of mitral insufficiency relies on comparisons of total stroke volume of the left ventricle, determined relatively, or quantitatively, with the forward stroke volume. The latter is measured either as the right ventricular stroke volume (in the absence of pulmonary and tricuspid regurgitation) or as cardiac output divided by heart rate and is obtained using a radionuclide or an independent method. Severe mitral regurgitation, as demonstrated by a large regurgitant fraction, can occur in the presence or absence of increased end-diastolic volume. The regurgitant fraction is not heart-rate dependent and does not clearly decrease during exercise, although some variations appear to exist. Evaluation of right ventricular function during exercise can also contribute to the assessment of patients with mitral insufficiency. Quantitative radionuclide methods are useful to assess the severity of mitral regurgitation and its repercussions.