Feasibility of strain and strain rate evaluation by two-dimensional speckle tracking in murine model of myocardial infarction

Segmental analysis by speckle-tracking echocardiography of the left ventricle response to isoproterenol in male and female mice

We studied by conventional and speckle-tracking echocardiography, the response of the left ventricle (LV) to a three-week continuous infusion of isoproterenol (Iso), a non-specific beta-adrenergic receptor agonist in male and female C57Bl6/J mice. Before and after Iso (30 mg/kg/day), we characterized LV morphology and function as well as global and segmental strain. We observed that Iso reduced LV ejection in both male (−8.7%) and female (−14.7%) mice. Several diastolic function parameters were negatively regulated in males and females such as E/A, E/E′, isovolumetric relaxation time. Global longitudinal (GLS) and circumferential (GCS) strains were reduced by Iso in both sexes, GLS by 31% and GCS by about 20%. For the segmental LV analysis, we measured strain, strain rate, reverse strain rate, peak speckle displacement and peak speckle velocity in the parasternal long axis. We observed that radial strain of the LV posterior segments were more severely modulated by Iso than those of the anterior wall in males. In females, on the other hand, both posterior and anterior wall segments were negatively impacted by Iso. Longitudinal strain showed similar results to the radial strain for both sexes. Strain rate, on the other hand, was only moderately changed by Iso. Reverse strain rate measurements (an index of diastolic function) showed that posterior LV segments were negatively regulated by Iso. We then studied the animals 5 and 17 weeks after Iso treatment. Compared to control mice, LV dilation was still present in males. Ejection fraction was decreased in mice of both sex compared to control animals. Diastolic function parameters, on the other hand, were back to normal. Taken together, our study indicates that segmental strain analysis can identify LV regions that are more negatively affected by a cardiotoxic agent such as Iso. In addition, cessation of Iso was not accompanied with a complete restoration of cardiac function after four months.

Feasibility and reference intervals assessed by conventional and speckle-tracking echocardiography in normal hamsters

OBJECTIVES

This study aimed to determine feasibility, reference intervals, and reproducibility of left ventricular ejection fraction (LVEF) and speckle-tracking echocardiography (STE) in adult Syrian hamsters.

BACKGROUND

Syrian hamster is an experimental model for several heart diseases. Echocardiography allows the evaluation of structure and function with bidimensional conventional techniques and STE. However, there is no data regarding reference values for bidimensional LVEF and myocardial strain in hamsters.

METHODS

A total of 135 female Syrian hamsters were anesthetized and studied with a small animal dedicated echocardiography system. Echocardiography measurements were obtained from M-mode and B-mode images. Feasibility and 95% reference intervals were obtained for LVEF using three different approaches: LVEF_Teichholz (from M-mode linear measurements), LVEF_BMode (from area-length method), and LVEF_ STE (from strain), and for global longitudinal (GLS), circumferential (GCS), and radial (GRS) endocardial strain. Reproducibility was assessed as intra-class correlation coefficients.

RESULTS

Feasibility of LVEF and endocardial strain was high (95% in FEVE_Teichholz, 93% in the LVEF_BMode, 84% in the LVEF_STE, 84% from PSLAX, and 80% from PSSAX). Values of LVEF_Teichholz were significantly higher than values of LVEF_BMode, and LVEF_STE-derived methods (59.0 ± 5.8, 53.8 ± 4.7, 46.3 ± 5.7, p < 0.0001). The 95% reference intervals for GLS, GCS, and GRS were respectively -13.6(-7.5;-20.4)%, -20.5 ± 3.1%, and + 34,7 ± 7.0%. Intra-class correlation coefficients were 0.49 - 0.91 for LVEF measurements, 0.73 - 0.92 for STE, with better results for LVEF_Teichholz and GLS.

CONCLUSIONS

Evaluation of LVEF by several methods and STE parameters is feasible in hamsters. Reference intervals for LVEF and STE obtained for this experimental animal model can be applied at future research.

Analyzing left ventricular function in mice with Doppler echocardiography

Mice are widely used in heart failure research. Accurate evaluation of cardiac structure and function is key to modern cardiovascular research. Doppler echocardiography is a simple, reproducible, and non-invasive method, which allows a longitudinal study of these small animals. Besides common parameters such as left ventricular chamber size, mass, and function, new emerging echo tools are of great interest for small animal imaging. In this review, we describe the technical issues linked to murine cardiovascular anatomy and physiology and the most current echo parameters that can be used.