QUANTITATIVE ASSESSMENT OF SURGICALLY INDUCED MITRAL REGURGITATION USING RADIONUCLIDE VENTRICULOGRAPHY AND FIRST-PASS RADIONUCLIDE ANGIOGRAPHY

Radionuclide ventriculography has been used in humans to evaluate valv ular incompetency, The stroke volume ratio, derived from the radionucl ide ventriculogram, is used to quantify the severity of mitral regurgi tation (MR). Previous studies conducted in humans have shown that left to right stroke volume ratio increases as the severity of MR increase s. In this study, we evaluated radionuclide ventriculography as a noni nvasive method to detect MR in dogs with surgically created mitral ins ufficiency. Six male and three female adult, conditioned mongrel dogs were used. Scintigraphic studies were performed prior to and 4 weeks a fter surgically created MR. Because of the overlap of the left and rig ht ventricles when viewed from a left lateral position, we combined da ta from a first-pass radionuclide angiocardiogram with the radionuclid e ventriculogram to obtain a corrected stroke volume ratio. Blood flow transit parameters were also derived from the first-pass radionuclide angiocardiogram. Standard left ventricular functional indices were al so measured from the radionuclide ventriculogram. On the left lateral view of the heart, 25 to 30% of the right ventricular volume overlaps the left ventricle, After correcting for the overlap, the stroke volum e ratio of normal dogs was 1.17 +/- 0.178 (mean +/- SD), which increas ed to 2.06 +/- 0.41 (mean +/- SD) (p < .001) 4 weeks after creation of MR. The was no significant change in left ventricular ejection fracti on or peak rate of ejection following MR. The transit times of blood t hrough the left ventricle were measured from the first-pass radionucli de angiocardiogram and were expressed as half-time clearance, peak cle arance rate, and time to peak clearance rate. The baseline half-time c learance was 2.07 +/- 0.71 s (mean +/- SD), which increased to 6.70 +/ - 4.89 s (mean +/- SD) (p = .02) after creation of MR. The baseline pe ak clearance rate was 49.75 +/- 8.96 cts/s (mean +/- SD), which decrea sed to 23.12 +/- 6.84 cts/s (mean +/- SD) (p < .001) after creation of MR. Stroke volume ratios significantly increased following creation o f MR. Blood flow transit through the left ventricle slowed following c reation of MR. The variability of these parameters were small in the b aseline studies, suggesting these techniques mag be clinically useful to gauge the severity of MR in dogs.