急性心肌缺血再灌注的MRI与定量病理对照研究

Acute Myocardial Ischemia and Reperfusion: A Comparative Study of MRI with Quantitative Pathology

目的 研究心肌急性缺血再灌注损伤的MRI特征及其病理学基础。材料与方法 阻断家兔冠状动脉左前降支 40min再灌注 1h后行MR平扫、Gd DTPA动态增强、电影MRI(cine MRI)及多巴酚丁胺负荷试验。放射微球测定心肌血流 ,伊文氏蓝和TTC染色确定正常、危险和梗死心肌 ,行病理和体视学测量。结果 危险和梗死心肌含水量较正常显著升高 ,细胞体密度、数密度、总数以及微血管宽度和体密度较正常显著减少 ,动态强化时间 信号强度曲线与正常表现不同 ,静息cine MRI均显示损伤区运动减弱、室壁变薄 ,心脏射血分数减低 ,多巴酚丁胺负荷后则运动增强、室壁增厚 ,心脏射血分数增加。结论 急性缺血再灌注损伤后 ,不同的损伤区具有不同的定量病理学特征 ,Gd DTPA动态增强、cine MRI及多巴酚丁胺负荷试验可以提高对心肌急性缺血再灌注损伤检出的敏感性和准确性 ,预测心肌活性。

Objective To study MRI features of acute myocardial ischemia and reperfusion and its pathologic basis.Materials and Methods After ligation of the left anterior descending branch of the coronary artery for 40 minutes and subsequent reperfusion for 1 hour, the experimental rabbits (n=7) underwent pre contrast MRI, Gd DTPA enhanced dynamic MRI, cine MRI and dobutamine stress test. Myocardial blood flow was measured with radioactive microspheres ( 99m Tc MAA). Ischemic and infracted regions were defined as Even's blue and 2, 3, 5 triphenyltetrazolium (TTC) negative regions, respectively. Water content of the myocardium was estimated. Histopathologic examination and stereology analysis of myocardial specimen were made. Results The volume and numerical density of the cardiac myocytes, total number and average width of microvessels in ischemic and infracted regions were significantly lower, while water content was markedly higher, than that in normal regions. Besides, the dynamic contrast enhancement time intensity curves of diseased regions were different from the curves of normal regions. The wall movement, wall thickness and cardiac ejection fraction at rest were markedly decreased on cine MRI, but increased significantly after dobutamine stress.Conclusion After acute myocardial ischemia and reperfusion, different quantitative pathologic changes occur in normal, ischemic and infracted regions. A combination of Gd DTPA enhanced dynamic MRI, cine MRI and dobutamine stress test can significantly improve the accuracy and sensitivity in detecting acute myocardial ischemia and reperfusion injury, and is valuable in forecasting the myocardial viability.