The Quantitive Investigation Of Canine Viable Myocardium In Acute Myocardial Infarction Model By Real-time Myocardial Contrast Echocardiography And Dobutamine Stress Experiment

BACKGROUND AND PURPOSE Myocardial infarction is not a "all and nothing" status during acute coronary occlusion, viable myocardium can exist in dangerous field, so we need to accurately kown the dangerous field, and identify the viable myocardium, in order to evaluate the patients' disease and effection after treatment, and hope to give a approval for clinic curing. Viable myocardium has a special charcater of contractile decrease, and can be devided to three categories: hibernating myocardium, stunned myocardium and maimed myocardium. Hibernating myocardium was first introduced by Diamond in 1978, the concept is that the myocardial contraction decreased by long time and chronic ischemia after coronary stenosis or occlusion, and the myocardium protects itself in low level metoblism to sustain its living. Stunned myocardium was first introduced by Brauuwald in 1982, and is defined that when blood flow turns to normal in dangerous field, the myocardial is damaged, and no infarction. But the contruction, metoblism and function decreased by ischemia and reperfusion need a few days to recovery, the myocarial perfusion isn't match with it's contraction. Both the two types myocardial harmfulness can be recovered completely, so to identify the viable myocradium and to save them is our important work, they can turn to normal and improve the globe and regional heart function, and give the patients high quality lives. The third viable myocardium-maimed myocardium are produced by incompletely ischemia and infarction, parts of their function can be reversed after curing in time, but cann't turn to normal. Now we have no good method to detect them.Myocardial micro-circulation can provide viable myocardium oxygen and energy, sustain their metabolism and carry out their rubbish, so it is a critical factor to ensure the myocardium living. Myocardial contrast echocardiography(MCE) has its special advantage in evaluating the myocardial micro-circulation, such as examinating the vascular integrality, quantitative evaluation in regional perfusion. In past few years, MCE developed quickly-from interval-trigger imaging to real-time imaging, from qualitation to quantitation, from two-dimension to three-demension, and offered more and more important effect. Two-dimension MCE is the first choice in clinic in current period beacause it can give doctor clear imaging to judge where is abnormal perfusion, but always need to change cross section to achive all myocardial segments' contrast imaging, so the quantitive rusults maybe not accurate in different time and different condition, we hope to evaluate the instantaneous myocardial perfusion in same imaging condition. Real-time three-dimension all volume MCE also can be used to evaluate the myocardial perdusion, but the imaging data are very more and need much time to manage off-line, therefore this technique is seldom used in clinic. Real-time three-plane MCE has advantage of both two-dimension MCE and three-dimension imaging, three planes has 60°angle each other in order to display all myocardial segments simultaneously, also we can manage the MCE imaging off-line plane by plane. We believe this technique has wide perspective.Because viable myocardium is different from normal myocardium and infarct myocardium in contraction, we can examine the regional myocardial contraction to identify viable myocardium. Echocardiography is often used in clinic and is a first method to evaluate the myocardial movement, but common echocardiographic examination will be interfered by subjective consciousness, tissue doppler imaging(TDI) is depended on the angle between sound beam and the myocardial movement in analysis. Speckle tracking imaging(STI) is a new techenique that to analysis myocardial contraction by tracking myocardial speckle's movement in three directions, can get rid of the effect of included angle between sound beam and the myocardial movement, so we can accurately diagnosis myocardial systolic movement by STI. Besides, stress echocardiography also is often used to examine the myocardial contractile reserve, to give doctor more information. In this investigation MCE, STI and Dobatamin stress echocardiography were combined to examine viable myocardium, result in significantly elevating the sensibility, specificity of diagnosing viable myocardium, I believe this investigation has important assisstence for clinic therapy.Part IThe quantitative evaluation on canine dangerous myocardium inacute myocardial infarction model by real-time single-planemyocardial contrast echocardiographyThe objective of this part is to quantitative evaluate the blood flow of canine dangerous myocardium on acute myocardial infraction by real-time single-plane myocardial contrast echocardiography(RT-TP-MCE) in rest. Eighteen anesthetized open-chest dogs were successfully performed the acute myocardial infarction models by ligating the left anterior descending (LAD) 3 hours. Before ligating LAD, the contrast agent (C₃F₈) was injected into femoral vein to perform myocardial contrast echocardiography(MCE) examination, after 3 hours the MCE examination was repeat. Then to kill the dog, Evans Blue dye and TTC staining were performed to identify normal and dangerous myocardium. Results display: before ligating LAD, all myocardial segments were filled well by microbubbles. 3-hour later by ligating LAD, the segments filled differntly. According to the golden standard of dyeing, the qualitative diagnosis by MCE was taken by eyes, the sensitivity and specificity to diagnosis dangerous myocardium were 89.6% and 91.7% respectively; the quantitative analysis was performed by the time-intensity curves fitting the function Y=A÷(1-e^-βt)+B, A (plat of peak intensity) and P(slope rate of the curve) values were used to quantitatively evaluate the blood flow of normal and ischemic myocardia, but the infarction myocardia was definded to zero; During rest, MBF<5.08 is a standard to diagnosis the dangerous myocardium, the sensitivity and specificity were 95.8% and 96.9% respectively, and the area of ROC curve was 0.984. The quantitative diagnosis by RT-MCE is very useful, and MBF<5.08 is a threshold to discriminate the dangerous myocardium in rest. Part IIQuantitative assessment of viable myocardium with time parametersduring first perfusion of real-time three-plane myocardial contrastechocardiography: an experimental studyThis part want to investigate the value of time parameters(the transit time in coronary and the time of half filling in myocardium) in assessing the blood flow of ischemia myocardium through establishing canine model of acutecoronary occlussion. 18 healthy anesthetized open-chest dogs were ligated the left anterior descend ing(LAD), 3 hours later the contrast agent(C₃F₈) was injected into femoral vein in a fixed velocity to perform myocardial contrast echocardiography (MCE) examination. The first perfusion and the replenishment processes were recorded by real-time tri-plane MCE(RT-TP-MCE) and realtime single-plane MCE(RT-SP-MCE) respectively, both the different processes were analyzed by the function Y=A×(1-e(-βt))+B. RT-SP-MCE uses A(plat of peak intensity) and P(slope rate of the curve) values to quantitatively evaluate the myocardial blood flow(MBF=Axp); the time point of the first microbubbles coming into the left ventricle was normalized to 0 in RT-TP-MCE, the time point of the first microbubble coming into the myocardium was defined as the transit time in coronary(T_c), the time point when microbubbles in myocardium achieved the 50% plat video intensity were defined as the time of half filling in myocardium(T_m). Evans Blue dye and TTC staining were performed to identify normal, ischemic and infarct myocardium. The time parameters of the two groups—normal myocardium and ischemic myocardium from RT-TP-MCE were: T_c (10.1±1.3)sand (20.4±7.1)s(P<0.01), T_m(17.1±2.2)s and (39.7±8.8)s(P<0.01); There were significantly negative correlation between the time parameters(T_c, T_m) and MBF from RT-SP-MCE in ischemic myocardium(r₁=-0.876, P<0.01; r₂=-0.894, P<0.01). The first perfusion imaging with RT-TP-MCE could be used to simultaneously, quantitatively evaluate the myocardial perfusion; The lower flow, the longer transit time in coronary and time of half filling in ischemic myocardium. Part IIIAn experimental study of detecting viable myocardium by real-timemyocardial contrast echocardiography, speckle tracking imaging anddobutamine stress echocardiographyIn this part, real-time myocardial contrast echocardiography(RT-MCE), speckle tracking imaging(STI) and dobutamine stress echocardiography(DSE) were combined to evaluate the viable myocardium. 18 healthy anesthetized open-chest dogs were successfully ligated the left anterior descending(LAD), 3 hours later the contrast agent(C₃F₈) was injected into femoral vein in a fixed velocity to perform myocardial contrast echocardiography (MCE) examination, in order to kown the myocardial micro-circulation perfusion; then STI was taken to get the message of myocardial contraction, DSE was used to observe the myocardial contractile reserve at last. After imaging, the dog's heart was stopped by injected 10% KC1, and then taken to perform Evans Blue dye and TTC staining, the myocardium were classified normal, ischemic and infarct groups. Through the analysis off-line, all segments were normal in perfusion and systolic function before ligating; After ligating 3-hour, in the myocardium having microbubbles filled, the sensitivity and specificity of dectecting viable myocardium were: 93.9% and 94.6% by QMCE, 75.8% and 94.6% by DSE and STI, 97.0% and 98.6% by QMCE, STI and DSE. From results, we kown that multiple techniques combined can elevate the sensitivity and specificity of examination.Conclusion1 RT-SP-MCE can be used to quantify the MBF, MBF<5.08 is a standard to diagnosis dangerous myocardium in rest.2 RT-SP-MCE can evaluate the collateral coronary artery, and has a good concordance with coronary flow imaging(CFI) during operation.3 RT-SP-MCE can quantitive calculate MBF to reflect the ischemic degree, the ischemic myocadial blood flow is obvious lower than normal MBF in acute myocardial infarction of camine model.4 The transit time in coronary(T_C) of first perfusion in RT-TP-MCE is useful for detecting viable myocardium, and there is significantly negative correlation between T_C and MBF in viable myocardium(r=-0.876,P<0.01).5 The time of half filling in myocardium(T_m) of first perfusion in RT-TP-MCE also is useful for detecting viable myocardium, and there is significantly negative correlation between T_Cand MBF in viable myocardium(r=-0.894,P<0.01).6 STI can analysis myocardial contraction, combined with DSE can analysis the myocardial contractile reserve.7 The combination of RT-MCE, STI and DSE can elevate the sensitivity and specificity of examinating viable myocardium, and they will be very useful for doctor to cure patients.