Assessment of regional left ventricular myocardial function in rats after acute occlusion of left anterior descending artery by two-dimensional speckle tracking imaging

Abstract

This study evaluated the change in regional left ventricular myocardial function in rats following acute occlusion of the left anterior descending coronary artery (LAD) by using two-dimensional speckle tracking imaging (2D-STI). Sixty Wistar rats were randomly divided into two groups, a myocardial infarction (MI) group, in which 50 rats were subjected to LAD occlusion for 30-45 min, and a sham-operated (SHAM) group that contained 10 rats serving as control. Echocardiography was performed at baseline and 1, 4 and 8 week(s) after the operation. High frequency two-dimensional images of left ventricular short axis at papillary muscle level were recorded. Peak systolic radial strain (PRS) and circumferential strain (PCS) were measured in the mid-ventricle in short-axis view by using EchoPAC workstation. Left ventricular internal diameter at diastole (LVIDd) and systole (LVIDs), fractional shortening (FS), ejection fraction (EF) and left ventricular mass (LVM) were measured by anatomical M-model echocardiography. Infarct size was measured using triphenyl tetrazolium chloride (TTC) staining 1 week and 8 weeks after the operation. Fibrosis of left ventricular myocardium was displayed using Van Gieson staining 1 week after the infarction. In terms of the TTC staining results, the left ventricle fell into three categories: infarcted, peri-infarcted and remote myocardial regions. Compared with those at baseline and in the SHAM group, (1) PRS and PCS in the infarcted, peri-infarcted and remote myocardial regions were significantly decreased in the MI group within 1 week after the operation (P<0.05) and the low levels lasted 8 weeks; (2) Compared with those at baseline, LVIDd, LVIDs, FS, EF and LVM in the MI group showed no significant difference 1 week after the operation (P>0.05). However, LVIDd, LVIDs and LVM were increased significantly 4 and 8 weeks after the operation (P<0.05), and FS and EF were decreased substantially (P<0.05). Van Gieson staining showed that fibrosis developed in all the three myocardial regions to varying degrees. It is concluded that 2D-STI is non-invasive and can be used to assess regional function of myocardium with different blood supply in rats following acute occlusion of the LAD, and can be used as a sensitive and reliable means to follow up the process of left ventricular remodeling.