Echocardiographic assessment of left ventricular hypertrophy in rats using a simplified approach

To determine whether left ventricular (LV) mass could be determined relatively simply in rats, without loss of accuracy, we reanalyzed previously reported echocardiographic measurements of 41 normotensive and 17 hypertensive male Wistar rats. Rats were divided into separate learning and test series. We assumed LV weight (g) = 1.04 x 4 x tau x [(D+h)2(L+h)-D2L]/3 x 10(3), where D was the LV short axis, h was the mean thickness of posterior wall and septum, measured in mm by M-mode echocardiography, and L was the long axis. Because L was not measurable by two-dimensional echocardiography, due to the high heart rate, it was estimated to be 12.28 mm by nonlinear regression analysis in the learning series of 29 rats. Correlation between necropsy LV weight and echocardiographic LV mass was 0.91 in the learning series and 0.89 in the test series (standard error of estimate [SEE] = 0.09 and 0.11 g). Mean values in the test series were 0.77 +/- 0.28 g and 0.78 +/- 0.25 g for LV weight and LV mass, respectively. LV mass was systematically underestimated by the cube-function formula (0.59 +/- 0.23 g, P < .0001 v necropsy LV weight). Echocardiographic LV mass using the ellipsoidal model with the above constant to estimate LV long axis had 78% sensitivity and 100% specificity for anatomic LV hypertrophy, suggesting that this method may be useful for research on rat models of hypertension.