Layer-specific strain analysis by speckle tracking echocardiography reveals differences in left ventricular function between rats and humans

Abstract

-specific strain analysis by speckle tracking echocardiography reveals differences in left ventricular function between rats and humans. Am J Physiol Heart Circ Physiol 299: H664 -H672, 2010. First published July 2, 2010; doi:10.1152/ajpheart.00017.2010.-The rat heart is commonly used as an experimental model of the human heart in both health and disease states, assuming that heart function of rats and humans is alike. When studying a rat model, echocardiography is usually performed on sedated rats, whereas standard echocardiography on adult humans does not require any sedation. Since echocardiography results of sedated rats are usually inferred to alert humans, in the present study, we tested the hypothesis that differences in left ventricular (LV) function may be present between rats sedated by a low dose of ketamine-xylazine and alert humans. Echocardiography was applied to 110 healthy sedated rats and 120 healthy alert humans. Strain parameters were calculated from the scans using a layer-specific speckle tracking echocardiography program. The results showed that layer longitudinal strain is equal in rats and humans, whereas segmental strain is heterogeneous (P Ͻ 0.05) in a different way in rats and humans (P Ͻ 0.05). Furthermore, layer circumferential strain is larger in humans (P Ͻ 0.001), and the segmental results showed different segmental heterogeneity in rats and humans (P Ͻ 0.05). Radial strain was found to be homogeneous at the apex and papillary muscle levels in humans and heterogeneous in rats (P Ͻ 0.001). Additionally, whereas LV twist was equal in rats and humans, in rats the rotation was larger at the apex (P Ͻ 0.01) and smaller at the base (P Ͻ 0.001). The torsion-to-shortening ratio parameter, which indicates the transmural distribution of contractile myofibers, was found to be equal in rats and humans. Thus, when evaluating LV function of sedated rats under ketamine-xylazine, it is recommended to measure the global longitudinal strain, LV twist, and torsion-to-shortening ratio, since no scaling is required when converting these parameters and inferring them to humans. speckle training; strain imaging; contractility RATS PLAY AN IMPORTANT ROLE in modeling human left ventricular (LV) function, and thus a variety of pathologies, such as myocardial infarction (20, 30) and cardiomyopathy (17, 19), are commonly induced in rats, so that their effect on LV function can be analyzed under controlled conditions. Consequently, the pertinent questions are 1) does the similarity in LV structure between rats and humans (4, 10) result in similar LV function? and 2) is the rat LV an appropriate model for studying human LV function?To evaluate the properties that quantify LV function, a method known as speckle tracking echocardiography (STE) has been recently developed (1, 3 , 9, 11, 13, 14, 18, 20, 23). The STE method uses standard two-dimensional (2-D) echocardiography cines and tracks the speckles in the ultrasound B-mode image sequence of the myocardium, and, subsequently, the parameters of local function ...

Speckle-Tracking Echocardiography Elucidates the Effect of Pacing Site on Left Ventricular Synchronization in the Normal and Infarcted Rat Myocardium

“…Elucidation of this issue seems critical in order to clarify whether rodent models may be further developed as simple experimental tools to study the molecular biology of DHF and CRT. Utilizing speckle-tracking 2-dimensional echocardiography, a method that has been repeatedly validated in rats for segmental strain analysis over the past decade [17][18][19][20], we confirmed the existence of mechanical dyssynchrony when RV pacing was applied. In addition, we elucidated the electrical and mechanical effects of LV pacing and BIV pacing.…”

“…We used speckle-tracking echocardiography analysis of Ecc, which has been reported to reliably and sensitively detect changes in LV dyssynchrony under various clinically relevant conditions in the rat heart [17][18][19][20]. The speckletracking echocardiographic methodology has previously been applied extensively in large animal models and in people and has been shown to be much more sensitive to changes in LV dyssynchrony than global echocardiographic measures, such as fractional shortening [24].…”

“…Two-dimensional transthoracic echocardiography was performed with a Vivid 7 echocardiography system (GE Healthcare, Milwaukee WI, USA) by shortaxis mid-ventricular scans at the level of the papillary muscle tips. Images were obtained with a 10 S transducer (5.4,11.8 MHz) using an image depth of 2.5 cm and a frame rate of 225 frames/s as was repeatedly validated in the literature in rat studies [17][18][19][20]. The acquisition protocol was as follows: Following optimal positioning of the transducer on the chest wall, it was fixed in place by the operator, while 2D clips (20 s each) were sequentially recorded in sinus rhythm followed by override pacing at the different pacing sites.…”

“…Based on the existing literature in rodents, we restricted our current analysis to circumferential strain (Ecc) which is more reliable than radial strain in the small heart of rats [18,19]. Ecc was evaluated as described in the literature [17][18][19].…”

“…Ecc was evaluated as described in the literature [17][18][19]. Briefly, analysis of mid-level short-axis images was done with dedicated software (''2D-strain'', EchoPAC, GE healthcare, Vingmed, Norway).…”