van Slochteren Frebus J, van der Spoel Tycho I G, Hansen Hendrik H G, Bovendeerd Peter H M, Doevendans Pieter A, Sluijter Joost P G, Chamuleau Steven A J, de Korte Chris L
Department of Cardiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Department of Cardiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Ultrasound Med Biol. 2014 Feb;40(2):378-88. doi: 10.1016/j.ultrasmedbio.2013.09.030. Epub 2013 Dec 7.
Local layer-specific myocardial deformation after myocardial infarction (MI) has not been studied extensively although the sub-endocardium is more vulnerable to ischemia and interstitial fibrosis deposition. Radiofrequency (RF) ultrasound-based analysis could provide superior layer-specific radial strain estimation compared with clinically available deformation imaging techniques. In this study, we used RF-based myocardial deformation measurements to investigate layer-specific differences between healthy and damaged myocardium in a porcine model of chronic MI. RF data were acquired epicardially in healthy (n = 21) and infarcted (n = 5) regions of a porcine chronic MI model 12 wk post-MI. Radial and longitudinal strains were estimated in the sub-endocardial, mid-wall and sub-epicardial layers of the left ventricle. Collagen content was quantified in three layers of healthy and infarcted regions in five pigs. An analytical geometric model of the left ventricle was used to theoretically underpin the radial deformation estimated in different myocardial layers. Means ± standard errors of the peak radial and longitudinal strain estimates of the sub-endocardial, mid-wall and sub-epicardial layers of the healthy and infarcted tissue were: 82.7 ± 5.2% versus 39.9 ± 10.8% (p = 0.002), 63.6 ± 3.3% versus 38.8 ± 7.7% (p = 0.004) and 34.3 ± 3.0% versus 35.1 ± 5.2% (p = 0.9), respectively. The radial strain gradient between the sub-endocardium and the sub-epicardium had decreased 12 wk after MI, and histologic examination revealed the greatest increases in collagen in the sub-endocardial and mid-wall layers. Comparable normal peak radial strain values were found by geometric modeling when input values were derived from the in vivo measurements and literature. In conclusion, the estimated strain values are realistic and indicate that sub-endocardial radial strain in healthy tissue can amount to 80%. This high value can be explained by the cardiac geometry, as was illustrated by geometric modeling. After MI, strain values were decreased and collagen content was increased in the sub-endocardial and mid-wall layers. Layer-specific peak radial strain can be assessed by RF strain estimation and clearly differs between healthy and infarcted tissue. Although the relationship between tissue stiffness and tissue strain is not strictly local, this novel technique provides a valuable way to assess layer-specific regional cardiac function in a variety of myocardial diseases.
心肌梗死后局部心肌层特异性变形虽未得到广泛研究，然而心内膜下更容易发生缺血及间质纤维化沉积。与临床可用的形变成像技术相比，基于射频（RF）超声的分析能够提供更优的心肌层特异性径向应变估计。在本研究中，我们使用基于RF的心肌变形测量来研究慢性心肌梗死猪模型中健康心肌与受损心肌之间的心肌层特异性差异。在心肌梗死后12周的猪慢性心肌梗死模型的健康区域（n = 21）和梗死区域（n = 5）的心外膜获取RF数据。在左心室的心内膜下、中层和心外膜下层估计径向应变和纵向应变。对5头猪的健康区域和梗死区域的三层心肌中的胶原蛋白含量进行定量分析。使用左心室的解析几何模型从理论上支持不同心肌层中估计的径向变形。健康组织和梗死组织的心内膜下、中层和心外膜下层的峰值径向应变和纵向应变估计值的均值±标准误分别为：82.7±5.2% 对39.9±10.8%（p = 0.002），63.6±3.3% 对38.8±7.7%（p = 0.004），以及34.3±3.0% 对35.1±5.2%（p = 0.9）。心肌梗死后12周，心内膜下与心外膜下之间的径向应变梯度降低，组织学检查显示心内膜下和中层的胶原蛋白增加最多。当输入值源自体内测量和文献时，通过几何建模得到了可比的正常峰值径向应变值。总之，估计的应变值是真实的，表明健康组织的心内膜下径向应变可达80%。如几何建模所示，这种高值可由心脏几何结构解释。心肌梗死后，心内膜下和中层的应变值降低，胶原蛋白含量增加。心肌层特异性峰值径向应变可通过RF应变估计进行评估，且在健康组织和梗死组织之间明显不同。尽管组织硬度与组织应变之间的关系并非严格局部性的，但这种新技术为评估各种心肌疾病中的心肌层特异性区域心脏功能提供了一种有价值的方法。
