Comparative Myocardial Deformation in 3 Myocardial Layers in Mice by Speckle Tracking Echocardiography

Abstract

Background. Speckle tracking echocardiography (STE) using dedicated high-resolution ultrasound is a relatively new technique that is useful in assessing myocardial deformation in 3 myocardial layers in small animals. However, comparative studies of STE parameters acquired from murine are limited. Methods. A high-resolution rodent ultrasound machine (VSI Vevo 2100) and a clinically validated ultrasound machine (GE Vivid 7) were used to consecutively acquire echocardiography images from standardized parasternal long axis and short axis at midpapillary muscle level from 13 BALB/c mice. Speckle tracking strain (longitudinal, circumferential, and radial) from endocardial, myocardial, and epicardial layers was analyzed using vendor-specific offline analysis software. Results. Intersystem differences were not statistically significant in the global peak longitudinal strain (−16.8 ± 1.7% versus −18.7 ± 3.1%) and radial strain (46.8 ± 14.2% versus 41.0 ± 9.5%), except in the global peak circumferential strain (−16.9 ± 3.1% versus 27.0 ± 5.2%, P < 0.05). This was corroborated by Bland Altman analysis that revealed a weak agreement in circumferential strain (mean bias ± 1.96 SD of −10.12 ± 6.06%) between endocardium and midmyocardium. However, a good agreement was observed in longitudinal strain between midmyocardium/endocardium (mean bias ± 1.96 SD of −1.88 ± 3.93%) and between midmyocardium/epicardium (mean bias ± 1.96 SD of 3.63 ± 3.91%). Radial strain (mean bias ± 1.96 SD of −5.84 ± 17.70%) had wide limits of agreement between the two systems that indicated an increased variability. Conclusions. Our study shows that there is good reproducibility and agreement in longitudinal deformation of the 3 myocardial layers between the two ultrasound systems. Directional deformation gradients at endocardium, myocardium, and epicardium observed in mice were consistent to those reported in human subjects, thus attesting the clinical relevance of STE findings in murine cardiovascular disease models.

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“…Speckle tracking was performed with EchoPAC software, which uses the LaGrangian strain approach (23). Global longitudinal strain curves were obtained from each of the 2 standard apical views and 1 parasternal long axis view.…”

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“…[51] We found that RS and RSr had greater variability, which was consistent with previous studies, but the exact reason was uncertain. [52]…”

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“…In patients with pulmonary hypertension for example, longitudinal strain is segmentally decreased despite normal global RV function [ 18 ]. With respect to animal models the application of 2D-strain is emerging, particularly in the assessment of left ventricular function [ 6 , 19 , 20 ]. However, the application of RV strain to animal models is not previously reported, but as with clinical studies, has major potential in characterizing RV function.…”

“…Recent advances in ultrasound technology, including 2D speckle tracking or strain, have seen these modalities now being applied to clinical practice [ 5 ]. However the application of 2D-Strain in small animals is emerging, and has been recently reported for left ventricular assessment [ 6 ]. A limitation of transthoracic imaging in small animals is the effect of anatomical artifact from the thoracic cage or liver on image quality.…”