Layer-specific strain analysis: investigation of regional deformations in a rat model of acute versus chronic myocardial infarction

Abstract

-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 ...

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]–[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.…”

“…Two-dimensional transthoracic echocardiography was performed with a Vivid 7 echocardiography system (GE Healthcare, Milwaukee WI, USA) by short-axis 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]-[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.…”

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.…”