三維斑點(diǎn)追蹤技術(shù)評(píng)估慢性腎臟病患者左心收縮功能的進(jìn)展

馬雨琴，張 波

(同濟(jì)大學(xué)附屬東方醫(yī)院醫(yī)學(xué)超聲科，上海 200120)

慢性腎臟病(chronic kidney disease, CKD)患者預(yù)后不佳，且醫(yī)療費(fèi)用較高，已成為嚴(yán)重的公共健康問題。流行病學(xué)調(diào)查[1]顯示，心臟疾病發(fā)病率隨CKD程度加重而增加[2]，即使腎功能僅有輕度減低，也與心血管風(fēng)險(xiǎn)增加存在顯著相關(guān)[3]。傳統(tǒng)超聲心動(dòng)圖評(píng)價(jià)左心室收縮功能減低常用指標(biāo)是左心室射血分?jǐn)?shù)(left ventricular ejection fraction, LVEF)。研究[4]表明，部分CKD患者心血管疾病的癥狀不典型，且LVEF可表現(xiàn)為正常，故傳統(tǒng)超聲心動(dòng)圖較難早期、準(zhǔn)確診斷CKD患者左心室收縮功能異常。新技術(shù)三維斑點(diǎn)追蹤成像(3-dimensional speckle tracking imaging, 3D-STI)可準(zhǔn)確、無創(chuàng)評(píng)價(jià)CKD患者左心收縮功能，有助于減少CKD患者心血管不良事件并改善預(yù)后[5]。本文對(duì)3D-STI在評(píng)估CKD患者左心室收縮功能中的應(yīng)用進(jìn)行綜述。

1 左心室解剖基礎(chǔ)

Torrent-Guasp等[6]提出心肌帶理論，認(rèn)為左心室由內(nèi)中外三層心肌組成，心內(nèi)膜下心肌呈右手螺旋走行，心外膜下心肌呈左手螺旋走行，中層心肌呈環(huán)形走行。不同走行排列的心肌纖維決定左心室復(fù)雜的空間運(yùn)動(dòng)形式：①縱向縮短，即左心室在長軸方向上的縱向運(yùn)動(dòng)；②左心室壁增厚，即左心室在短軸方向上的徑向運(yùn)動(dòng)；③左心室短軸半徑縮小，即左心室在短軸方向上的圓周運(yùn)動(dòng)；④左心室心內(nèi)膜面積變化，即綜合長軸應(yīng)變和圓周應(yīng)變(circular strain, CS)的內(nèi)膜面積改變；⑤左心室扭轉(zhuǎn)和解旋，為完成心臟射血，左心室在收縮期發(fā)生“擰毛巾樣”扭轉(zhuǎn)；從心尖向心底方向觀察，左心室心尖部逆時(shí)針旋轉(zhuǎn)，左心室基底部順時(shí)針旋轉(zhuǎn)；舒張期左心室反方向解旋，心室充盈[7]。

2 STI原理

STI為無創(chuàng)、實(shí)時(shí)的定量檢查技術(shù)。由于心肌的細(xì)小結(jié)構(gòu)會(huì)對(duì)入射超聲波產(chǎn)生散射，在圖像上形成散射斑點(diǎn)，故通過標(biāo)記心動(dòng)周期中某“斑點(diǎn)”運(yùn)動(dòng)軌跡，可逐幀追蹤心動(dòng)周期中該“斑點(diǎn)”對(duì)應(yīng)部位心肌的形變，從而獲得心肌運(yùn)動(dòng)速度、應(yīng)變以及心肌扭轉(zhuǎn)等變形情況[8]。與組織多普勒技術(shù)(tissue Doppler imaging, TDI)技術(shù)相比，STI不僅與組織多普勒頻移無關(guān)、無明顯角度依賴性，還對(duì)局部噪聲敏感度較小，可更全面及準(zhǔn)確評(píng)價(jià)心肌功能[9]。二維斑點(diǎn)追蹤技術(shù)(2-dimensional speckle tracking imaging, 2D-STI)局限于二維平面內(nèi)，無法完全跟蹤斑點(diǎn)運(yùn)動(dòng)的空間位置[10]。3D-STI通過連續(xù)性分析心臟全容積圖像，追蹤心肌聲學(xué)斑點(diǎn)在三維空間內(nèi)的運(yùn)動(dòng)軌跡，應(yīng)用縱向應(yīng)變(longitudinal strain, LS)、徑向應(yīng)變(radial strain, RS)、CS、面積應(yīng)變(area strain, AS)、旋轉(zhuǎn)及扭轉(zhuǎn)運(yùn)動(dòng)等參數(shù)來評(píng)價(jià)心肌各節(jié)段形變，從而實(shí)現(xiàn)定量評(píng)價(jià)心肌組織的運(yùn)動(dòng)情況[11]。

3 3D-STI評(píng)價(jià)CKD患者左心室收縮功能

3.1 左心室應(yīng)變及應(yīng)變率 CKD患者左心室由于長期壓力負(fù)荷及容量負(fù)荷增加、心肌代償性增厚、心腔擴(kuò)大及心肌缺血[12]，于二維超聲心動(dòng)圖上多表現(xiàn)為左心室擴(kuò)大、室壁增厚，舒張功能、局部室壁運(yùn)動(dòng)及LVEF減低[13]。評(píng)估左心室整體收縮功能最常用的參數(shù)是LVEF，其代表心搏量占左心室舒張末期容積的比例，有重要的預(yù)后評(píng)估作用[14]，而計(jì)算LVEF有賴于圖像質(zhì)量、容量負(fù)荷及操作者經(jīng)驗(yàn)。研究[15]表明，部分CKD患者已出現(xiàn)心功能不全癥狀和體征時(shí)，LVEF仍可表現(xiàn)為正常。3D-STI應(yīng)用心肌整體或局部應(yīng)變及應(yīng)變率，可準(zhǔn)確、定量評(píng)價(jià)CKD左心室心肌收縮能力。劉開薇等[16]觀察LVEF正常(>55%)的早期CKD患者，發(fā)現(xiàn)CKD 2期和CKD 3期患者左心室整體LS較正常對(duì)照組明顯減低。Sun等[17]應(yīng)用3D-STI技術(shù)發(fā)現(xiàn)維持透析組左心室整體LS和RS明顯減低，隨訪2年，結(jié)果顯示左心室整體LS可作為心血管不良事件的獨(dú)立預(yù)測(cè)因素。早期CKD患者LS減低的可能原因如下：①LS代表心內(nèi)膜下心肌縱向纖維在長軸的縮短；②微血管病變，血鈣沉積于心內(nèi)膜，尿毒癥毒素及脂質(zhì)代謝障礙等因素致心內(nèi)膜下心肌灌注不良，故內(nèi)膜心肌層最早受累。Chen等[18]發(fā)現(xiàn)血液透析組和對(duì)照組心尖水平LS、RS及CS均高于基底段水平和乳頭肌水平，而未行血液透析組患者則無上述變化。

3.2 左心室旋轉(zhuǎn)和扭轉(zhuǎn) 左心室扭轉(zhuǎn)為左心室心尖水平與心底水平旋轉(zhuǎn)角度的差值。王淑珍等[19]應(yīng)用2D-STI發(fā)現(xiàn)尿毒癥患者心底部旋轉(zhuǎn)角度達(dá)峰早于主動(dòng)脈瓣關(guān)閉，而心尖部旋轉(zhuǎn)角度達(dá)峰及扭轉(zhuǎn)角度達(dá)峰遲于主動(dòng)脈瓣關(guān)閉。左心室扭轉(zhuǎn)和解旋是在三維空間內(nèi)的變形運(yùn)動(dòng)，不僅影響心臟的正常收縮功能，還可促進(jìn)舒張?jiān)缙谛氖页溆RI可無創(chuàng)、準(zhǔn)確地測(cè)量心肌旋轉(zhuǎn)角度[20]，但時(shí)間及空間分辨率較低，獲取信息量相對(duì)較少，后期數(shù)據(jù)處理繁瑣，檢查耗時(shí)較長且費(fèi)用較貴，使其臨床應(yīng)用受限。3D-STI運(yùn)用左心室基底段、中間段及心尖段平均旋轉(zhuǎn)角度、整體扭轉(zhuǎn)度、整體扭力及旋轉(zhuǎn)或扭轉(zhuǎn)角度達(dá)峰時(shí)間等參數(shù)評(píng)價(jià)左心室旋轉(zhuǎn)及扭轉(zhuǎn)[21]。Andrade等[22]發(fā)現(xiàn)采用3D-STI技術(shù)測(cè)得的左心室扭轉(zhuǎn)角度較2D-STI小，但二者左心室扭轉(zhuǎn)角度的達(dá)峰時(shí)間差異無統(tǒng)計(jì)學(xué)意義，可能由于2D-STI技術(shù)不能完全跟蹤斑點(diǎn)運(yùn)動(dòng)的空間位置，故從三維角度可更加準(zhǔn)確和全面地觀察扭轉(zhuǎn)運(yùn)動(dòng)。Pai等[23]運(yùn)用3D-STI技術(shù)研究發(fā)現(xiàn)，與正常對(duì)照組相比，維持透析的CKD患者左心室整體旋轉(zhuǎn)、扭轉(zhuǎn)角度及基底段和局部扭力均降低，可能由于心肌間質(zhì)纖維化、缺血、血鈣沉積及微血管病變等因素使心肌僵硬，從而導(dǎo)致心肌收縮力減弱；左心室容積擴(kuò)張使心內(nèi)膜纖維角度傾斜度變小，減弱心外膜相對(duì)于心內(nèi)膜旋轉(zhuǎn)的運(yùn)動(dòng)優(yōu)勢(shì)。3D-STI技術(shù)可通過評(píng)價(jià)CKD患者左心室旋轉(zhuǎn)及扭轉(zhuǎn)運(yùn)動(dòng)，從而在機(jī)械力學(xué)角度發(fā)現(xiàn)CKD患者左心室收縮功能減低。

3.3 左心室同步性運(yùn)動(dòng) CKD患者左心室壓力及容量負(fù)荷長期增加可引起左心室構(gòu)型改變，導(dǎo)致左心室收縮不同步，進(jìn)一步影響左心室收縮功能及局部心肌代謝和灌注[24]。研究[25]發(fā)現(xiàn)，左心室收縮不同步是充血性心力衰竭患者發(fā)生嚴(yán)重心臟不良事件的獨(dú)立預(yù)測(cè)因子。Murata等[26]應(yīng)用2D-STI技術(shù)發(fā)現(xiàn)，未透析終末期腎病組LS及RS不同步指數(shù)較對(duì)照組升高，而兩組CS不同步指數(shù)間差異無統(tǒng)計(jì)學(xué)意義；透析后，RS不同步指數(shù)較透析前下降，提示RS對(duì)前負(fù)荷改變較為敏感。Kobayashi等[27]應(yīng)用實(shí)時(shí)三維超聲心動(dòng)圖觀察27例終末期腎病患兒，發(fā)現(xiàn)病例組左心室不同步指數(shù)易受前負(fù)荷及左心室厚度影響，且數(shù)值高于正常對(duì)照組。3D-STI技術(shù)結(jié)合了實(shí)時(shí)三維超聲與2D-STI技術(shù)的優(yōu)勢(shì)，能更準(zhǔn)確地評(píng)價(jià)左心室收縮的同步性。3D-STI技術(shù)可應(yīng)用左心室壁兩節(jié)段應(yīng)變達(dá)峰值時(shí)間最大差值(前室間隔和左心室側(cè)壁應(yīng)變達(dá)峰時(shí)間差)、各節(jié)段應(yīng)變達(dá)峰值時(shí)間標(biāo)準(zhǔn)差(左心室不同步指數(shù))以及AS不同步指數(shù)等參數(shù)來定量評(píng)價(jià)左心室收縮同步性[28-29]：上述參數(shù)值越高，提示左心室收縮不同步越嚴(yán)重。此外，3D-STI技術(shù)在評(píng)價(jià)心臟同步化治療(cardiac resynchronisation therapy, CRT)后療效中具有重要作用。Thebault等[30]采用3D-STI觀察接受CRT治療的慢性心力衰竭患者左心室同步性，發(fā)現(xiàn)雙腔起搏患者LS、RS及AS絕對(duì)值均大于右心室起搏患者，且LS、RS及AS左心室不同步指數(shù)均小于右心室起搏患者。Sun等[17]發(fā)現(xiàn)維持透析組左心室不同步指數(shù)較正常對(duì)照組升高。

3.4 血液透析前后左心收縮功能變化 作為有效的腎臟替代治療，血液透析能減輕水鈉潴留，排出毒素(如尿素氮、肌酐及甲狀旁腺素等)，糾正電解質(zhì)、酸堿平衡紊亂，改善內(nèi)環(huán)境及減輕心臟前負(fù)荷，從而改善心臟功能。Chen等[18]觀察LVEF正常的尿毒癥患者，發(fā)現(xiàn)規(guī)律血液透析組各方向的三維整體應(yīng)變及不同心肌水平RS均優(yōu)于非透析組，提示堅(jiān)持規(guī)律血液透析能夠改善左心室收縮功能。Kovács等[31]發(fā)現(xiàn)，單次血液透析后，終末期腎病患者左心室整體LS、RS、CS及AS均增加。相反，Wu等[32]發(fā)現(xiàn)維持性血液透析患者單次血液透析后左心室整體LS、RS、CS、旋轉(zhuǎn)角度、扭轉(zhuǎn)角度及整體扭力較透析前無顯著變化，僅左心室局部扭力短期增加。胡科丹等[33]發(fā)現(xiàn)左心室整體AS隨透析時(shí)間延長而呈升高—降低—緩慢升高的趨勢(shì)，隨著透析時(shí)間推移，提示尿毒癥患者左心室心功能呈現(xiàn)“減低—好轉(zhuǎn)—再減低”的規(guī)律。上述研究表明，3D-STI技術(shù)可及時(shí)反映尿毒癥患者血液透析前后左心功能變化情況，但單次血透后左心室應(yīng)變的變化情況尚未明確，仍需進(jìn)一步研究。

4 局限性及發(fā)展前景

3D-STI技術(shù)的局限性：①可由于肥胖、肺氣腫等患者因素或操作者水平所致圖像質(zhì)量較差，從而影響結(jié)果準(zhǔn)確性；②獲取的圖像幀頻較低，易出現(xiàn)拼接錯(cuò)位，且部分CKD患者室壁增厚、心室擴(kuò)大，為包絡(luò)整個(gè)心室，需調(diào)大扇角，故幀頻進(jìn)一步減低，圖像質(zhì)量進(jìn)一步變差，從而影響結(jié)果準(zhǔn)確性；③要求被檢者心電圖存在規(guī)則的R-R間期，且需被檢者屏氣達(dá)數(shù)個(gè)心動(dòng)周期，以減小呼吸運(yùn)動(dòng)對(duì)圖像的干擾；對(duì)于心律失常及呼吸困難者，無法獲得理想的全容積圖像，從而影響結(jié)果準(zhǔn)確性。

雖然存在局限性，但目前3D-STI技術(shù)仍是重復(fù)性相對(duì)可靠的超聲定量分析技術(shù)，采集和分析圖像較2D-STI技術(shù)更簡便和省時(shí)[34]；可依靠準(zhǔn)確的心臟解剖空間定位，通過量化分析左心室應(yīng)變結(jié)果，客觀評(píng)價(jià)左心室整體及局部心肌功能[35]。

5 小結(jié)

早期診斷及治療CKD患者心臟損傷能減少心臟不良事件。超聲心動(dòng)圖可實(shí)時(shí)定性、定量評(píng)價(jià)心功能，而超聲新技術(shù)可發(fā)現(xiàn)CKD患者心臟結(jié)構(gòu)的改變及與其相關(guān)的心臟整體及心肌節(jié)段功能異常。正確認(rèn)識(shí)3D-STI技術(shù)的優(yōu)缺點(diǎn)，聯(lián)合應(yīng)用傳統(tǒng)超聲心動(dòng)圖和3D-STI技術(shù)，可為臨床早期、準(zhǔn)確診斷CKD心臟病變提供重要參考。

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