Echocardiographic and cardiac Doppler assessment of mice

Recent studies have suggested that intermediate-frequency M-Mode transthoracic echocardiographic imaging is a promising method for evaluating the left ventricle in transgenic mice. However, there is a paucity of data regarding two-dimensional (2-D) echocardiography and cardiac Doppler echocardiography in this model. Therefore we studied 15 mice (body weights 38 to 65 gm) with an ultrasound system equipped with a 9 MHz transducer. M-mode, 2-D, pulsed, and color-flow Doppler studies were performed. Mean +/- SD for septal, posterior wall, and left ventricular cavity dimensions at end diastole were the following: M-mode: 1.1 +/- 0.2, 1.0 +/- 0.2, and 3.7 +/- 0.7 mm; 2-D: 1.0 +/- 0.2, 1.1 +/- 0.3, and 3.0 +/- 0.6mm. Left ventricular fractional shortening was assessed from the M-mode echocardiogram: mean 53.7% +/- 10.7% (range 42% to 77%). 2-D assessment of left ventricular mass correlated better with left ventricular mass identified at necropsy than left ventricular mass identified by M-mode echocardiography (r = 0.70; p = 0.007 versus r = 0.07; p not significant). 2-D visualization of left ventricle, proximal aorta, and aortic and mitral valves was excellent and was obtained mainly from a "parasternal" window. Apical views were more difficult to obtain. Mean +/- SD for aortic peak and mean velocities and velocity-time integral were 0.53 +/- 0.13, 0.32 +/- 0.08, and 0.025 +/- 0.008 m/sec. Estimated stroke volume was 0.0506 +/- 0.018 ml/beat. Cardiac output was 12.64 +/- 7.87 ml/min. Mean +/- SD for mitral peak E, peak A, and E/A ratio were 0.45 +/- 0.09 m/sec, 0.19 +/- 0.06 m/sec, and 2.4 +/- 0.66 m/sec, respectively. In all mice the E/A ratio was greater than 1 (range 1.76 to 3.6). Color-flowing imaging clearly displayed normal mitral inflow and left ventricular outflow. In one mouse, aortic regurgitation was recorded by pulsed Doppler echocardiography. Echocardiographic, pulsed, and color-flow Doppler assessment of mice is feasible. In this study left ventricular mass was assessed better by 2-D measurement of left ventricular dimensions. Assessment of left ventricular performance is feasible. Color Doppler-guided evaluation of aortic flow and aortic root measurement permits assessment of stroke volume and cardiac output.