Validation of the Wall Motion Score and Myocardial Performance Indices As Novel Techniques to Assess Cardiac Function in Mice Post Myocardial Infarction

The aim of this study was to determine the feasibility and accuracy of wall motion score index (WMSI) and myocardial performance index (MPI) for measuring regional and global left ventricular (LV) function using high-resolution echocardiography after myocardial infarction (MI) in mice. 48 mice underwent MI by a mid-LAD ligation. Echocardiography was performed under anesthesia at baseline and one month post-MI. WMSI was analyzed by a 16-segment model on short axis views, scoring wall motion as 1-normal, 2-hypokinetic, 3-akinetic, 4-dyskinetic and 5-aneurysmal. WMSI was calculated as the sum of scores divided by the total number of segments. MPI was calculated based on isovolumetric contraction time (IVCT), isovolumetric relaxation (IVRT) and ejection times (ET) (MPI = (IVCT+IVRT)/ET). We measured LV ejection fraction (LVEF), volumes (ESV and EDV), fractional shortening (FS), and infarct size (IS). LVEF at 4 weeks post-MI was reduced at 32.8 ± 9.0%. Linear correlation analyses showed that WMSI (1.6 ± 0.3) correlated with LVEF (r = -0.84, p<0.0005), FS (r = -0.43, p=0.003) and IS (34.3 ± 15.3%) (r = 0.86, p<0.0005). MPI (0.67 ± 0.09) correlated with LVEF (r = -0.67, p<0.0005) and IS (r = 0.72, p<0.0005). MPI also correlated with mitral inflow velocity E (r = -0.68, p<0.0005) and deceleration time (DT) (r = -0.42, p=0.003). Stepwise regression analysis revealed that WMSI was independently associated with IS. IS, FS, E and DT were all independent determinants of MPI. In conclusion, echocardiographic assessments of WMSI and MPI in mice are feasible, and correlate strongly with 2D measurement of LV function and IS. These novel parameters provide additional non-invasive assessment of regional and global LV function in mice post-MI. Page 2 of 25 Copyright Information