Radionuclide quantification of mitral and aortic regurgitation

Gated equilibrium bloodpool scintigraphy was used to obtain the ratio of left and right ventricular stroke counts (end‐diastolic minus end‐systolic counts within ventricular areas of interest), the radionuclide equivalent of stroke volumes. This ratio or stroke count index (SCI) should be unity in normal subjects and increased in patients with aortic or mitral regurgitation, when left ventricular stroke output rises to compensate for regurgitant flow. Results of this non‐invasive method were compared with semiquantitative angiographic grading of mitral (1 to 4+) or aortic (1 to 3+) regurgitation in ninety‐seven patients. We found a SCI of 1.15 ± 0.18 (SD) in thirty‐six control subjects without evidence of mitral or aortic regurgitation at cardiac catheterization. Subsequently, a ratio of 1.50 was chosen as the upper limit of normal for the analysis of thirty‐seven patients with mitral regurgitation and twenty‐four patients with aortic regurgitation. Clearly, elevated SCI values were obtained in the presence of grade 3 and 4 mitral regurgitation (eighteen out of twenty patients) and of grade 2 and 3 aortic regurgitation (seventeen out of eighteen patients). Only two out of seventeen subjects with grade 1 or 2 mitral incompetence had an elevated SCI, while none of six subjects with grade I aortic regurgitation had an abnormal SCI. If these lesser degrees of valvular incompetence are considered of minor significance, overall sensitivity of the radionuclide method in our patient population was 92%, specificity 95%. Occasional discrepancies between SCI and angiographic severity of left‐sided valvular regurgitation are probably a result of methodological limitations. We could not demonstrate any relation with global left ventricular function as measured from the radionuclide ejection fraction. We conclude that the SCI may be used as a non‐invasive tool for diagnosis and management of patients with valvular heart disease, both before and after interventions.