Abstract 11500: Increased Washout of 99mTc-Sestamibi Would Reflect Impaired Myocardial Contractile and Relaxation Reserve During Dobutamine Stress Due to Mitochondrial Dysfunction in Dilated Cardiomyopathy Patients

Introduction Myocardial mitochondrial damage reduces ATP production, and causes myocardial dysfunction. Increased 99mTc-sestamibi (Tc-99m-MIBI) myocardial washout is reportedly caused by mitochondrial dysfunction. We therefore investigated whether Tc-99m-MIBI washout rate (WR) would predict the mitochondrial damage and myocardial dysfunction in dilated cardiomyopathy (DCM) patients. Methods Twenty-one DCM patients (NYHA I to III) underwent Tc-99m-MIBI myocardial scintigraphy and cardiac catheterization. Myocardial Tc-99m-MIBI uptake was quantified as early heart-mediadtinum ratio (H/M) and delayed H/M, and WR was calculated. Endomyocardial biopsy specimens were obtained for quantitative mRNA analysis and electron microscopy. LV dP/dtmax (index of myocardial contractility) and T1/2 (index of myocardial relaxation) were calculated by left ventricular pressure curve at baseline and during dobutamine infusion (15 μg/kg/min). The patients were divided into two groups as follows: group A of 10 patients showing WR ≥ 24.44%; group B of 11 patients showing WR ≥ 24.44%. Results The abundance of mRNAs for mitochondrial electron transport-related enzymes (α-KGDH, NDUFV3, COX5B) were significantly higher in group A than in group B. Electron microscopy showed that a percentage of damaged mitochondria, glycogen droplet, and lipid droplets were much greater in group B than in group A. WR of Tc-99m-MIBI were significantly correlated with the percentage change in LV dP/dtmax(%LV dP/dtmax) (r=0.49, P=0.02) and T1/2(%T1/2) (r=0.34, P=0.04) from baseline to dobutamine stress. No significant correlation was seen between early or delayed H/M and %LV dP/dtmax or %T1/2. %LV dP/dtmax in group B was significant larger than that in group A. Conclusions Increased washout rate of Tc-99m-MIBI could predict the mitochondrial dysfunction and the impairment of myocardial contractile and relaxation reserves during dobutamine stress test in DCM patients noninvasively. ![Graphic][1] [1]: /embed/inline-graphic-1.gif