武丹妮 栗平 田海燕
[摘要] 二维彩色多普勒心脏超声因其操作的快速、便携、经济等优势应用于心脏功能和结构的评价,并通过M型超声心动图、二维Simpson双平面法完成心室收缩和舒张功能及心室容积的测定。但对于左心室收缩功能存在细微变化者则二维彩色多普勒心脏超声各项参数则不能真实反映其变化。随着现代超声医学影像的逐步发展,二维斑点追踪成像技术(2D-STI)通过动态追踪心肌组织实时回声斑点运动评价左心室收缩,弥补了二维彩色多普勒心脏超声的诸多不足。本文现就2D-STI对左心室收缩功能的研究进展予以综述。
[关键词] 二维斑点追踪成像技术;左心室收缩功能;应变
[中图分类号] R541.1 [文献标识码] A [文章编号] 1673-7210(2019)08(b)-0045-04
[Abstract] Two-dimensional color Doppler echocardiography has been applied to evaluate cardiac function and structure for its advantages of fast, portable and economical operation. The measurement of ventricular systolic and diastolic function and ventricular volume has been completed by M-mode echocardiography and two-dimensional Simpson biplane method. However, for some special diseases or slight changes in left ventricular systolic function, the parameters of two-dimensional color Doppler echocardiography can not truly reflect the changes. With the gradual development of modern ultrasound medical imaging, two-dimensional speckle tracking imaging (2D-STI) makes up for many shortcomings of conventional two-dimensional color Doppler echocardiography. It can dynamically track the real-time echo speckle movement of myocardial tissue, and then evaluate left ventricular systolic function. This article reviews the research progress of 2D-STI on left ventricular systolic function.
[Key words] Two-dimensional speckle tracking imaging; Left ventricular systolic function; Strain
超声心动图因其操作方便、快速、有效、经济等优势,已成为临床评价左心室收缩功能的首选方法[1]。但有些特殊疾病或左心室收缩功能存在细微变化时,左室射血分数则无法真实反映左心室收缩功能变化[2]。2D-STI通过实时逐帧追踪高帧频二维图像的斑点回声定量分析,全面观察心肌运动及机械变形能力,追踪和测量左心室应变及应变率,由此可准确评价左心室收缩功能变化。本文现将2D-STI技术在左心室收缩功能评价的应用研究进展进行综述。
1 概述
左心室收缩功能的准确评估是临床诊断和治疗心脏疾病的关键[3],其主要评价指标包括左心室容积参数、扭转参数、心肌应变参数等。应变是指物体的变形能力,心肌应变即心肌在心脏收缩与舒张运动时发生相对于原来形状的变形。根据心肌运动模式,心脏的应变包括4个部分[4],分别是纵向应变(LS)、径向应变(RS)、周向应变(CS)、旋转角度(RA)。左心室应变的常规指标主要包括左心室长轴整体收缩期最大峰值应变(GLS)、左心室轴向整体收缩期最大峰值应变(GCS)、左心室整体扭转度(ROT)、心脏整体收缩期应变率(GSRs)、舒张早期应变率(GSRe)、舒张晚期应变率(GSRa)[5]。
常规超声心动图评价左室收缩功能是通过间接途径测量心腔内径的缩短来反映心脏长轴方向纵向心肌和短轴方向环形心肌的收缩能力,2D-STI是基于二维灰阶图像实时追踪不同像素心肌组织在高帧频二维图像中的位置,对斑点回声定量分析,计算并描绘心肌运动速度和变化,可真实反映心室整体扭转的程度、心肌收缩性能及心脏输出能力[6-7]。并通过量化后的应变参数真实反映心肌局部和整体运动功能[8],进而无创性定量评价和测量左心室局部及整体收缩功能。
2 2D-STI在左心室收缩功能中的临床应用
2.1 对正常人左心室收縮功能的评价
构成心脏的心肌纤维呈螺旋状排列,内层肌纤维呈纵向排列,中层心肌呈环形走行,而外层心肌纤维由基底向心尖部呈逆时针方向斜行。因此心脏的收缩和舒张包括纵向、径向、周向三个空间方向的复杂机械运动[9]。Matre等[10]应用2D-STI技术对比正常人群心脏的局部心肌应变值,结果显示,室间隔心肌应变值较左室侧壁、后壁相应节段心肌应变值高,同时对比左心室内、外层心肌GCS,内层心肌整体及局部不同室壁节段GCS值更高。Amundsen等[11]应用声纳微测量法及加标记的心脏磁共振成像技术对斑点追踪超声心动图(speckle tracking echocardiography,STE)的准确性进行验证,结果显示2D-STI的测量数据与声纳微测量法及加标记的心脏磁共振成像技术测量结果基本一致,证实2D-STI能够准确反映心肌运动及收缩功能状态。李倩等[12]采用2D-STI技术测量生理状态下实验猪左心室内、外层心肌的GCS,结果显示心脏各个节段内层心肌的GCS均高于外层心肌,以室间隔、左室侧壁、左室下壁及前间隔差异最为显著。
2.2 对冠心病患者左心室收缩功能的评价
超声心动图因其能够反映心肌缺血或梗死导致的节段性室壁运动异常,在冠心病的诊断、预后及疗效观察等方面均有重要意义[13]。组织多普勒(TDI)极大地提高了超声心动图检测节段性室壁运动及左心室收缩功能的敏感性和准确性[14]。但许多学者在对心肌运动速度测量研究中发现TDI存在较大的角度依赖性,影响其准确性[15]。2D-STI技术克服了TDI技术的缺点[16],其时间和空间分辨率均较高,通过连续观察左室所有节段同步运动情况及心肌各个节段应变性,获取左心室实时全容积数据,从而整体评价冠心病患者心肌收缩功能。Hua等[17]应用2D-STI技术评估40只急性心梗建模成功的成年大鼠的左心室收缩功能,结果显示2D-STI技术在有效反映心脏纵向变形运动的同时,还能反映径向及周向的变形运动。Helle-Valle等[18]应用2D-STI技术对8只急性心肌梗死实验猪模型进行应变分析,结果示收缩期应变随LS的变化较大,随着LS的增加,应变没有显著降低。Ng等[19]对122名健康受试者及40例非ST段抬高型心肌梗死患者通过TDI技术及2D-STI技术对比分析其左心室收缩及舒张同步指数,认为2D-STI技术可能比TDI技术能够更敏感地鉴别左室收缩不同步。Tatsumi等[20]同时应用介入机械延迟技术、Yu指数和2D-STI技术评估心脏再同步化治疗,发现2D-STI技术可以同时测量纵向、周向、径向三个方向的应变不同步指数,能够更加准确地预测心脏再同步化治疗术后效果。
2.3 对肥厚型心肌病左心室收缩功能的评价
肥厚型心肌病(hypertrophic cardiomyopathy,HCM)是一种具有遗传异质性的常染色体显性遗传心肌病,解剖特点为心室非对称性肥厚[21]。大量文献证实,HCM患者左室收缩功能减低与预后情况差、死亡率增加呈正相关[22]。Serri等[23]应用2D-STI技术对26例非梗阻型肥厚型心肌病(NHCM)患者及45名健康受试者进行检查,发现尽管部分患者的左心室整体收缩功能正常,但应变的所有成分均显著降低,纵向、径向、周向应变平均值较对照组明显降低。Huang等[24]应用实时三维超声心动图和2D-STI技术评价HCM患者的左室收缩和舒张功能,发现在HCM患者中,心肌功能障碍在非肥厚的部分也有分布,即使左室射血分数正常,左室收缩和舒张功能也会受损。
2.4 对心力衰竭患者左心室收缩功能的评价
心力衰竭(heart failure,HF)患者有左心室运动功能不良伴LVEF的降低,李慎义等[25]研究应用2D-STI评价急性HF患者左心室收缩功能时发现,随着患者LVEF降低,其左心室整体周向、纵向、径向应变值随之降低,且心肌的应变亦减低。左心室扭转指心尖部相对于基底部的旋转,其取决于心肌收缩力,因此左心室ROT可用来评价其收缩功能。Song等[26]对HF患者心肌纵向、径向、周向及心肌扭转进行定量检测,研究表明射血分数正常的心力衰竭(HFNEF)患者左心室收缩功能局部存在受损情况,而Toufan等[27]利用2D-STI评估HFNEF患者左心室的纵向收缩功能,发现HFNEF患者左心室各个节段的纵向收缩功能均减低。王银荣等[28]研究结果与Toufan等[27]一致,且径向及周向收缩功能均有减低。
2.5 对妊娠期高血压患者左心室收缩功能的评价
早期识别并控制妊娠期高血压(hypertensive disorder complicating pregnancy,HDCP)可改善母婴预后,降低围生期母胎死亡率[29]。2D-STI能够发现HDCP孕妇早期左心室心肌结构的细微变化。张蕾等[30]研究应用2D-STI评价HDCP患者左心室心肌应变,发现当实验组与对照组研究对象LVEF值均>50%时,HDCP 患者左心室长轴心肌纵向收缩期应变较正常妊娠妇女显著降低,舒张晚期应变与舒张功能障碍呈正相关,收缩力代偿性增强,提示在心脏整体收缩功能无明显变化时局部心肌收缩力已出现减低的趋势。Ajmi等[31]应用2D-STI技术对比研究30例HDCP患者和30名健康孕妇的左心室的充盈压力和应变峰值,结果表明GLS对HDCP患者亚临床心功能不全的检测比其他超声心动图参数更敏感。
2.6 对2型糖尿病患者左心室收缩功能的评价
2型糖尿病(T2DM)控制不满意时引起心脏微血管病变和心肌代谢紊乱,早期识别其功能变化并及时干预可显著改善预后。杨勇等[32]研究应用2D-STI在T2DM患者早期左心室整体与不同节段长轴收缩功能改变时发现,T2DM患者左心室容积及LVEF在疾病早期无明显变化,左心室整体与节段长轴收缩功能应变值减低,提示T2DM患者左心室收缩功能的异常在疾病早期已经出现。韩红生等[33]研究应用2D-STI评估T2DM患者出现心肌损害时左心室整体平均纵向应变值从健康对照组、单纯糖尿病组、糖尿病合并微血管病变组逐次减低,糖尿病合并微血管病组相较其他组别变化更明显。
3 小结
综上所述,2D-STI通过对心肌组织斑点回声的追踪,能够早期、敏感地评价左心室整体和局部的收缩功能,为临床各类心脏疾病的诊疗及预后评估提供重要参考依据,然而由于二维斑点追踪技术在测量过程中对时间和空间分辨率要求均较高,部分患者可能会在同一个心动周期内不能有效显示所有心肌节段同步运动状况,可能导致追踪的失败。随着超声影像技术的逐步发展,2D-STI技术会逐渐完善,并且会更广泛地应用于心脏疾病的臨床诊断和治疗效果评价。
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(收稿日期:2018-04-16 本文編辑:任 念)