High Frame Rate Doppler Echocardiography in the Rat: an Evaluation of the Method

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Abstract
Aims: In small animal models, two-dimensional (2D) and Doppler echocardiography should provide more information than M-mode, especially in animals with infarcted and distorted left ventricles, but has been limited by low frame rates and poor near field resolution. New, high frame rate echo-Doppler equipment with digital processing was tested for accuracy of measurements. Methods and Results: Fourteen normal Wistar rats (232–328 g) were examined under halothane anaesthesia. Pulsed Doppler recordings from both left ventricular outflow tract (LVOT) and right ventricular outflow tract (RVOT) corresponded well with simultaneous ultrasound transit time measurements of aortic flow (LVOT: y =0·99 x +4·8, R=0·93, Standard error of estimate (SEE)=8·3 ml . min −1 , and RVOT: y =0·97 x −4·3, R=0·93, SEE=8·4 ml . min −1 ). No systematic differences were observed over a flow range of 20–90 ml . min −1 . Left ventricular (LV) dimensions assessed by 2D parasternal long-axis and short-axis views were equal to M-mode measurements with LV diameter 6·6±0·44 mm, anterior wall 1·8±0·18 mm, and posterior wall 1·5±0·56 mm. Mean absolute difference 4·4–8·5%. Intra- and interobserver variability was 4·6±4·1% and 6·7±7·0% for Doppler measurements, and 4·3±3·8% and 3·8±4·6% for dimensions, respectively. Conclusion: High frame rate Doppler echocardiography provides accurate non-invasive measurements of cardiac structure and function in the rat.

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