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目的应用超声生物显微镜(UBM)及斑点追踪(STI)技术探讨不同月龄正常小鼠左心室内膜及外膜心肌应变的特征。方法对48只不同月龄的健康成年雄性小鼠行常规超声心动图检查,采集胸骨旁左心室长轴、乳头肌水平左心室短轴二维图像。常规超声心动图测量舒张末期室间隔厚度(IVST)、左心室后壁厚度(LVPWT)、左心室舒张末期内径(LVEDD)、左心室收缩末期内径(LVESD)、左心室射血分数(LVEF)、左心室内径缩短率(LVFS)。脱机分析两个不同切面左心室内、外膜的纵向应变、圆周应变及径向应变的峰值应变(PK)、达峰时间(TPk)、室壁最大达峰延迟时间(MOWD)等指标。结果不同月龄间心率、IVST、LVPWT、LVEDD和LVESD的差异无统计学意义。与3月龄组比较,12月龄组LVEF、LVFS均减小(P<0.05)。随月龄增加,小鼠左心室内膜下和外膜下心肌纵向、圆周及径向PK均呈逐渐减小的趋势:与3月龄组相比,12月龄组的测值均明显减小(P<0.05);与6月龄组相比,12月龄组径向应变测值也明显减小(P<0.05)。外膜下心肌的纵向及圆周应变均显著小于内膜下心肌(P<0.01)。随月龄增加,左心室内膜下和外膜下心肌纵向、圆周及径向TPk、MOWD均呈逐渐增大趋势。与3、6月龄组相比,12月龄组的部分测值明显增大(P<0.05)。同月龄正常小鼠内膜下及外膜下心肌纵向、圆周TPk及MOWD接近(P>0.05)。结论 UBM及STI技术能够无创、简便地全面评价正常小鼠左心室内、外膜下心肌的应变;所获不同月龄正常小鼠心脏结构及功能的正常测量值范围可为今后其他小鼠心脏模型的研究提供参考依据。
Objective To investigate the characteristics of left ventricular endocardium and epicardial myocardium strain in normal mice of different ages by using ultrasound biomicroscopy (UBM) and speckle tracking (STI). Methods Forty-eight healthy adult male mice of different ages underwent routine echocardiography. Two-dimensional images of the short axis of the left ventricle and the papillary muscles were collected. The left ventricular posterior wall thickness (LVPWT), left ventricular end diastolic dimension (LVEDD), left ventricular end systolic diameter (LVESD), left ventricular ejection fraction (LVEF) Left ventricular diameter shortening (LVFS). The left and right ventricular endocardial and epicardial longitudinal strain, circumferential strain and radial strain peak strain (PK), peak time (TPk) and maximum wall delay time (MOWD) were analyzed offline. Results There was no significant difference in heart rate, IVST, LVPWT, LVEDD and LVESD between different months of age. Compared with the 3-month-old group, the LVEF and LVFS in the 12-month-old group decreased (P <0.05). With the increase of age, the longitudinal, circumferential and radial PK of left ventricular subendocardial and subepicardial myocardium of mice showed a decreasing trend: Compared with 3-month-old group, 12-month-old group were significantly reduced (P <0.05). Compared with 6-month-old group, the measured radial strain in 12-month-old group also decreased significantly (P <0.05). The longitudinal and circumferential strain of the subependymal myocardium was significantly lower than that of the subendocardial myocardium (P <0.01). With the increase of age, the longitudinal, circumferential and radial TPk, MOWD of the subendocardial and subepicardial myocardium gradually increased. Compared with 3 and 6 months old group, some measured values of 12 months old group increased obviously (P <0.05). At the same month of age, the vertical and circumferential TPk and MOWD of submandibular and subepicardial myocardium in normal mice were similar (P> 0.05). Conclusions UBM and STI techniques can evaluate the strain of left ventricular and epicardial myocardium in normal mice noninvasively and simply. The normal measured values of cardiac structure and function of normal mice of different ages can be obtained from other mouse hearts in the future The study of the model provides a reference.