Validation of echocardiographic methods for assessing left ventricular dysfunction in rats with myocardial infarction

The rat infarct model is widely used in heart failure research, but few echocardiographic indexes of left ventricular (LV) function are validated in this model. Accordingly, the objective of this study was to validate a 13-segment LV wall motion score index (WMSI) and the myocardial performance index (MPI) in infarcted rats. Twenty-nine male Wistar rats underwent left coronary artery ligation or sham operation and were evaluated with two-dimensional and Doppler flow echocardiography 8 wk later. After echocardiography, invasive indexes were obtained using a high-fidelity catheter. WMSI and MPI were correlated with the invasive and noninvasive measurements of LV function. WMSI and MPI significantly correlated directly with end-diastolic pressure (r = 0.72 and 0.42 for WMSI and MPI, respectively) and the time constant of isovolumic relaxation (r = 0.68 and 0.48) and inversely with peak rate of rise of LV pressure (+dP/dt; r = -0.68 and -0.50), peak rate of decline in LV pressure (r = -0.57 and -0.44), LV developed pressure (r = -0.58 and -0.42), area fractional shortening (r = -0.85 and -0.53), and cardiac index (r = -0.74 and -0.74). Stepwise linear regression analyses revealed that LV end-diastolic pressure, +dP/dt, area fractional shortening, and cardiac index were independent determinants of WMSI (r = 0.994) and that cardiac index and +dP/dt were independent determinants of MPI (r = 0.781). We conclude that the 13-segment WMSI and MPI are reproducible and correlate strongly with established echocardiographic and invasive indexes of systolic and diastolic function. These findings support the use of WMSI and MPI as indexes of global LV function in the rat infarction model of heart failure.