Echocardiographic left ventricular mass measurement in small animals: Anatomic validation in normal and aortic regurgitant rabbits

To determine the accuracy of echocardiographic methods of measurement of left ventricular mass (LVM) in small animals, two-dimensional (2-D) and M mode echocardiography was performed in 30 normal New Zealand White rabbits and in 30 rabbits with surgically induced aortic regurgitation. Left ventricular (LV) internal dimension and wall thicknesses, measured from M mode echocardiograms using American Society of Echocardiography (ASE) and Penn convention measurements and from 2-D long axis images, were used to calculate LVM by the cube function formula. LVM and LV cross-sectional areas calculated from M mode echocardiograms and determined by planimetry of 2-D short axis images were compared with LV weights obtained at sacrifice. In normal animals, anatomic LV weight was closely related to echocardiographic LVM measured by ASE (r = 0.94; p < 0.001), Penn (r = 0.93; p < 0.001) and 2-D long axis methods (r = 0.92; p < 0.001) and to M mode (r = 0.95; p < 0.001) and 2-D cross-sectional area (r = 0.95; p < 0.001). In aortic regurgitant rabbits, good correlations were obtained between anatomic LV weights and echocardiographic LVM using the ASE (r = 0.80; p < 0.001), Penn (r = 0.80; p < 0.001), Penn (r = 0.76; p < 0.001) and 2-D long axis methods (r = 0.73; p < 0.001) and with M mode (r = 0.67; p < 0.001) and 2-D cross-sectional area (r = 0.61; p < 0.005). Interobserver and intraobserver reproducibility of LVM measurements was excellent (r = 0.95-0.96; p < 0.001). Thus, echocardiography can be utilized to assess anatomic LV weight in both normal rabbits and those with aortic regurgitation and is sufficiently accurate to study both normal LV growth and pathological hypertrophy in small animals.