-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 ...
-specific strain analysis: investigation of regional deformations in a rat model of acute versus chronic myocardial infarction. Am J Physiol Heart Circ Physiol 303: H549 -H558, 2012. First published July 9, 2012; doi:10.1152/ajpheart.00294.2012.-Myocardial infarction (MI) injury extends from the endocardium toward the epicardium. This phenomenon should be taken into consideration in the detection of MI. To study the extent of damage at different stages of MI, we hypothesized that measurement of layer-specific strain will allow better delineation of the MI extent than total wall thickness strain at acute stages but not at chronic stages, when fibrosis and remodeling have already occurred. After baseline echocardiography scans had been obtained, 24 rats underwent occlusion of the left anterior descending coronary artery for 30 min followed by reperfusion. Thirteen rats were rescanned at 24 h post-MI and eleven rats at 2 wk post-MI. Next, rats were euthanized, and histological analysis for MI size was performed. Echocardiographic scans were postprocessed by a layer-specific speckle tracking program to measure the peak circumferential strain (S C peak ) at the endocardium, midlayer, and epicardium as well as total wall thickness S C peak . Linear regression for MI size versus S C peak showed that the slope was steeper for the endocardium compared with the other layers (P Ͻ 0.001), meaning that the endocardium was more sensitive to MI size than the other layers. Moreover, receiver operating characteristics analysis yielded better sensitivity and specificity in the detection of MI using endocardial S C peak instead of total wall thickness S C peak at 24 h post-MI (P Ͻ 0.05) but not 2 wk later. In conclusion, at acute stages of MI, before collagen deposition, scar tissue formation, and remodeling have occurred, damage may be nontransmural, and thus the use of endocardial S C peak is advantageous over total wall thickness S C peak . speckle tracking; transmurality; myocardial viability; left ventricular function THE MYOCARDIAL LAYERS contribute differently to deformation of the left ventricle (LV) at the normal state (4,8,11,23,29), during wall motion abnormalities (1,6,24), and particularly during myocardial infarction (MI) (6). Since nontransmural MI is associated with a high risk for mortality (21), it is essential to identify it at its early stages. The identification of nontransmural MI is challenging, since the myocardial injury is heterogeneous within the myocardial layers (13,15,35), where usually nontransmural MI affects the endocardium first (35).Therefore, the viable layers cause the injured layers to passively contract and move (i.e., tethering). Tethering makes it difficult to identify the MI using the traditional speckle tracking echocardiography (STE) method. The STE method is an angle-independent tool developed for the automatic evaluation of LV regional function (25, 26, 37) by tracking speckle movement in two-dimensional grayscale echocardiographic cine loops (34). The STE is advantageous, among other ...
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