急性心肌梗塞的MRI特征及其超微病理基础

目的　探讨急性心肌梗塞后不同心肌损伤区的MRI特征及其超微病理学基础。方法　结扎兔冠状动脉左前降支 2 4h制作AMI模型 10只 ,行常规MRI、对比剂动态增强MRI、电影MRI及多巴酚丁胺负荷试验。放射微球测定心肌血流量 ,伊文氏蓝和TTC染色确定缺血和梗塞心肌 ,并制作电镜标本观察肌原纤维和线粒体的改变 ,测定病变值和对损伤程度分级。结果　AMI后T1信号无明显改变 ,T2 信号增高 ,40 %可见病变局部心肌壁变薄 ,60 %可见病变邻近左室腔内异常血流高信号 ;正常、缺血和梗塞心肌动态增强时间 -信号强度曲线表现不同 ;cine -MRI表现为局部室壁变薄、运动减弱 ,多巴酚丁胺负荷表现为室壁变厚、运动增强。病变心肌较正常肌含水量显著增高而血流显著减少。正常、缺血及梗塞心肌线粒体体密度、数密度存在显著差异。结论　AMI的MRI表现与心肌超微结构损伤程度及残余血流量有关

MRI and Ultrastructural Pathology on Acute Myocardial Infarction

Objective To study the MRI features and its ultrastructural pathology basis in different myocardial injury areas after acute infarction.Methods 10 rabbits were given ligation of left anterior descending branch 24 hours to make pathologic models.All animals underwent conventional MRI,contrast media dynamic enhancement MRI,cine-MRI and dobutamine stress test.Myocardial blood flow was measured with radioactive micropheres to define risk regions.Ischemic and infarcted regions were defined as Even's blue and 2,3,5triphenyltetrazolium chloride(TTC)negative regions respectively,and made electron microscopy specimens to observe the changes of mitochondria and myofibril.The myocardial ultrastructural injury was scored and graded.Results There were no significant change on T 1WI,but the signal intensity on T 2WI increased significantly after AMI.The diseased myocardium became thinning were seen in 40% cases,and the abnormal flowing high signal were seen in 60% cases.The dynamic enhancement time-signal intensity curves were different in normal,ischemic and infarcted regions.Cine-MRI showed the cardiac wall movement impairing and the wall thick thinning,but the wall movement reinforcing and the wall thick thickening after dobutamine stress.The water content of ischemic and infracted myocardium were marked higher than normal myocardium.The myocardial blood flow in diseased regions were decreased significantly than that in normal regions.The volume density and numerical density of mitochondria in different injury regions showed significant differences.Conclusion MRI appearances of AMI were associated with the injury degree of myocardial ultrastructure and the residual myocardial blood flow.