A four-dimensional model-based method for assessing cardiac contractile dyssynchrony in mice

Four-dimensional (4D), or equivalently, 3D + time, analysis is useful for comprehensive assessment cardiac function, especially in the asymmetric left ventricle (LV) after myocardial infarction (MI). This paper presents a 4D-model-based method for ultrasound assessment of cardiac contractile function in mice. Echocardiographic image sequences were acquired at high frequency (30 MHz) from the hearts of C57Bl/6 mice. Image sequences were acquired at contiguous slice locations encompassing the entire 3D LV. In order to reconstruct continuous, dynamic 3D LVs from the images using a 4D mathematical cardiac model, endocardial and epicardial contours were segmented for all image slice locations through one cardiac cycle. In the 4D model, shape and continuity constraints were applied in order to normalize irregularities caused by noise or non-uniform distribution of image data. Root mean square error (RMSE) was calculated between the model-fitted 4D LV and the actual LV surface measured from image data. RMSE was 0.23 mm (~4.5% of epicardial diameter) for the epicardial surface, and 0.20 mm (6.4% of endocardial diameter) for the endocardial surface. 3D regional wall thickening was calculated from the 4D LV surface, and LV dyssynchrony was assessed by analyzing the time to peak strain (T_peak). This 3D analysis of contractile function in post-MI mouse hearts revealed >80% reduction of peak radial displacement, a 10-15 ms delay in Tpeak in the infarct zone, and a SD_T_peak of 6-10 ms over the entire 3D LV. In summary, the 4D-model-based method was successfully used for analyzing cardiac dyssynchrony in the 3D murine LV, and it proved advantageous over conventional 2D methods because it was more comprehensive and noise-robust.