| To study the relationship between the changes of Tc - 99m - sestamibi ( MIBI ) s uptake and clearance and myocardial viability , to evalue the role of MIBI s kinetics about assessing myocardial viability.Methods1 . Experimental Groups and Study ProtocolFifteen Sprague - Dawley ( SD ) rats were divided into three groups at random : control ( Normal , n = 5 ) , ischemic - reperfused with glucose ( IR + G , n = 5 ) , and ischemic - reperfused without glucose (IR-G,n=5). The rat hearts were excised by parasternal left thracotomy and transferred to the Langendorff perfusion apparatus to start perfusing with Krebs - Henseleit ( KH ) buffer. The follows are the flow chart;\ group: baseline 40niin MIBI uptake 40m in clearance IR Ggroup: haseline l0min no flow 40min reperfusiol0min clearance 40min MIBI uptake2. Myocardial Activity MonitoringUse the Gamma positioning system to detect the myocardial counts in the 40min reperfusion period with 99mTc - MIBI and the follow 40 min reperfusion period without 99mTc - MIBI , every five minutes for one measure. Background activity was measured after the heart was removed from the aparatus at the end of the 80th min . The myocardial radioactivity ( in microcuries ) was measured by a dose calibrator. The hearts were weighed by electronic balance.3. Myocardial Viability MeasurementDetect the myocardial viability by creatine kinase ( CK ) assay, triphenyltet-razolium chlorid (TTC) staining and electron microscope analysis, observe the distibution of MIBI in the cardiac myocyte by radioautography.4. Data AnalysisAfter background subtraction and decay correction, apply SPSS10. 0 software for Stat. and Excel software for histogram. Comparisons between groups were performed with one - way analysis of variance, comparisons within a group were made by means of paired t test. Probability values less than 0.05 were considered significant. Calculate the value of Tc - MIBI(%ID/g) every five minutes after reperfusion with MIBI - KH. The correlation between activity of myocardial MIBI on the 80 min and the CK leak or the TTC myocardial viability percent was assessed by linear regression analysis.ResultsMIBI - KH (14. 8MBq,400jxCi) buffer was applied for 40 minutes ( uptake ) , followed by 40 - minute clearance by no MIBI - KH buffer. MIBI uptake (percent injected dose pergram) was significantly decreased in the IR + G(7.09 0. 97 ID%/g) and IR - G(6. 64 0. 68 ID%/g, compared with IR + G group,p >0.05 ) groups compared with the control group (11.44 1.79 ID%/ g,p <0. 05) . Washout fraction of MIBI was more rapid in the IR - G group (72. 75% 9. 89% ,p <0. 001) ) than in the control(20. 68% 1.92% ) and IR + G (21. 03% 3. 68%) groups ,the later two groups have no significantly difference (p >0.05) . At the end of 40 minutes clearance , retention rate (percent injected dose pergram) of MIBI in the IR - G(l. 82 0. 73 ID%/g)and IR + G(5. 61 0. 89 ID%/g) groups were significantly less than that of control group (9. 09 1.57 ID%/g, p <0. 05) , respectively, and the retention in the IR - G group was less than that in the IR + G group ( p <0.05 ). Creatine kinase assay, triphenyltetrazolium chloride staining, and transmission electron microscopy analysis demonstrated more serious myocardial damage in the IR - G group than in the IR + G group. The end MIBI activity of 40 minutes clearance washighly correlated with myocardial viability determined by TTC(r = 0. 84,p <0. 001) and CK assay (r= -0. 96, p < 0. 001), Radioautography demonstrated that Tc - 99m - sestamibi distributed in the cytoplasm and intercellular substance ( by OM ) .ConclusionsIschemic - reperfused myocardium could be distinguished from normal myocardium by MIBI uptake and clearance kinetics. Lack of metabolic substrate induced more severe injury in hearts subjected to the same ischemic - reperfusion protocol and resulted in significantly faster myocardial clearance. The activity of MIBI correlated well with the CK concentration, MIBI retention correlated well with viable myocardi... |
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