Quantification of aortic valvular regurgitation in dogs by nuclear imaging

Radionuclide gated cardiac blood pool (GBP) imaging was used to quantitatively assess the severity of acute aortic valvular regurgitation produced experimentally in 10 anesthetized dogs. Right ventricular (RV) and left ventricular (LV) stroke counts (end-diastolic minus end-systolic counts in RV and LV regions of interest) were used as indices of the stroke volumes of the two ventricles. Regurgitant fraction (RF(GBP)) was derived by assuming that an excess of LV stroke counts compared to RV stroke counts was due to regurgitant flow: RF(GBP)=LV stroke counts - RV stroke counts/LV stroke counts x 100. Regurgitant fraction (RF(EMF)) was also estimated directly from an electromagnetic flowmeter (EMF) on the ascending aorta. Mean RF(EMF) was 55.8±17.9% (±SD). Close agreement was found between regurgitant fractions measured by GBP and EMF (RF(GBP) = 1.09, RF(EMF) -4.7%, r = 0.88, p<0.001, SEE = 9.98%). The severity of regurgitation from blood pool images also correlated closely with aortic pulse pressure (r = 0.89) and the length of the tear in the aortic valve (r=0.84). These results suggest that blood pool imaging may be useful for noninvasive quantification of regurgitant flow in patients with valvular insufficiency.