Assessment Of Regional Myocardial Systolic Function In A Rat Myocardial Infarction Model By 2-dimensional Strain Echocardiography

Backgrounds and ObjectivesThere were cadiocyte ischemia and necrosis and ventricle remodeling after myocardial infarction, which cause the regional or global dysfunction of the heart. Accurate quantification of regional myocardial function is important in evaluation of the severity of desease and assessment of the therapeutic effectiveness and the prognosis. This experimental study was aimed to investigate the value of 2-dimensional strain echocardiography (2DSE) on assessment of regional myocardial function in a rat myocardial infarction model, and it's application in a research of mesenchymal stem cells (MSCs) transplantation therapy .Methods and ResultsPart One: An animal model of myocardial infarction was established by opening chest and ligating the proximal left anterior descending coronary artery (LAD) in 17 SD rats. And 8 healthy rats served as normal controls. Regional myocardial function at left ventricular papillary level were detected by echocardiography at baseline, 1-day and 4-weeks after procedures. The parametric measurements included: the end-systolic radial strain and radial strain rate (SR and SrR) and end-systolic circumferential strain and circumferential strain rate (SC and SrC) of each 6 segments derived by 2DSE, systolic thickening fraction (WTF) of each 6 segments derived by anatomic M-mode echocardiography(AME), the parameters of TDI is the systolic peak myocardial tissue velocity (Vp) and radial strain and radial strain rate (SR-TDI and SrR-TDI) of anterior and inferior. According to the size of myocardial infarction in histology finding, the optimal cutoff points of parameters for detection of infarct were analyzed and the sensitivity and specifity of every parameter to detect infarct were obtained using receiver operating characteristic analysis (ROC). Comparing with parameters measured at baseline, the regional systolic function of anterior segment significantly decreased at 1-day and 4-week post-infarction in model group (P<0.05). There were significant decreases in SR, SrR ,SC and SrC of non-infarct regions derived by 2DSE after myocardial infarction (P<0.05). Significant correlations were found between 2DSE parameters and size of myocardial infarction(P<0.01), among which the SR was the best parameters for detecting infarct, and SR less than 10% has 84% sensitivity and 98% specificity for detecting infarct area greater than 30%.Part Two: 40 SD rats were divided into myocardial infarct (MI) group (n=14), MSCs therapy group (n=16), and normal control (n=10). A rat model of myocardial infarct was established for MI-group and MSCs therapy group, and control group with sham-operation. The MSCs were labeled by DAPI, and were directly implanted into the acute infarct site via focal injection for the rats of MSCs therapy group. Regional myocardial function on left ventricular papillary level were detected by 2DSE pre-procedurally at baseline, 1-week and 4-weeks after procedures. Four weeks later, left ventricle hemodynamics parameters was evaluated using physiological recorder after echocardiography examination. Fluorescence microscope was used to identify the DAPI-labeled cells,and immunohistochemistry staining of Troponin I (Tn-I) were used to evaluate the differentiation and expression of engrafted MSCs. By 4 weeks, compared with measurements in MI group, increased SR and SrR were found in MSCs therapy group(P<0.05). In MSCs therapy group, there was a significant increase in LVSP, +dp/dtmax and decrease in LVEDP compared with MI group(P<0.05). The labeled cells were viable in the host hearts and immunochemical staining revealed that the engrafted stem cells expressed Troponin I. Conclusions1.All echocardiographic technique of AME, TDI and 2DSE are able to detect regional left ventricular systolic function quantitatively in a rat model of myocardial infarction, but 2DSE has greater sensitivity and specificity in detecting myocardial infarct size. Furthermore, 2DSE can detect the regional wall motion abnormality in non-infarct regions after myocardial infarction.2.2DSE may detect the improved regional systolic function after transplantation of MSCs on a post-MI of rat model and be superior to the conventional echocardiographic parameters of LVEF. The labeled MSCs and cardiac-like muscle cells can be found in infracted area after transplantation of rat MSCs, which may contribute to the improvement of left ventricular function.