鄭帥,孟旭
(首都醫(yī)科大學(xué)附屬北京安貞醫(yī)院心臟外科,北京 100029)
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·綜述·
心臟自主神經(jīng)與心臟疾病
鄭帥,孟旭
(首都醫(yī)科大學(xué)附屬北京安貞醫(yī)院心臟外科,北京 100029)
臨床上,多種常見心臟疾病與心臟自主神經(jīng)有密切的關(guān)系。本文著重介紹心臟疾病狀態(tài)下心臟自主神經(jīng)的病理改變,以及心臟自主神經(jīng)結(jié)構(gòu)和功能的改變對多種心臟疾病的影響,旨在為心臟疾病的治療提供新的思路。
自主神經(jīng)系統(tǒng);心律失常;心力衰竭;綜述
支配心臟的自主神經(jīng)包括交感神經(jīng)和副交感神經(jīng),自主神經(jīng)對心臟功能有重要調(diào)節(jié)作用。研究發(fā)現(xiàn),心臟疾病時,心臟自主神經(jīng)的形態(tài)和功能會發(fā)生相應(yīng)變化,進(jìn)而可能引起心臟節(jié)律和功能的改變。本文對病理狀態(tài)下心臟自主神經(jīng)形態(tài)和功能的變化,及其與心臟節(jié)律和心功能的關(guān)系做一綜述。
在病理狀態(tài)下,心臟自主神經(jīng)的形態(tài)和功能常常發(fā)生改變。心肌梗死時梗死區(qū)神經(jīng)軸突壞死,而梗死周邊區(qū)交感神經(jīng)能夠再生。神經(jīng)生長因子(NGF)是出生后交感神經(jīng)賴以生存的一種營養(yǎng)因子,對交感神經(jīng)的損傷修復(fù)有重要意義。ZHOU等[1]研究顯示,從心肌梗死后第3天開始,心肌內(nèi)NGF水平明顯升高,直至梗死后1個月;而神經(jīng)染色提示心肌梗死后交感神經(jīng)再生的水平和心肌內(nèi)NGF水平保持一致。心肌梗死后交感神經(jīng)和副交感神經(jīng)的再生情況有明顯差異,OH等[2]發(fā)現(xiàn),心肌梗死后交感神經(jīng)能夠再生,而副交感神經(jīng)沒有明顯再生,這也說明NGF促進(jìn)副交感神經(jīng)再生的能力較弱。心肌梗死后NGF主要來源于損傷周圍的非神經(jīng)細(xì)胞,一些細(xì)胞因子如白細(xì)胞介素-1和內(nèi)皮素-1能促進(jìn)NGF表達(dá)[3-5]。
心房顫動(AF)會引起心房迷走神經(jīng)突觸內(nèi)乙酰膽堿(Ach)濃度和離子通道變化,迷走神經(jīng)的密度和分布發(fā)生變化。于付生等[5]研究顯示,心房快速起搏可以誘導(dǎo)AF,并使心房迷走神經(jīng)分布的不均一性增加。AF也會引起交感神經(jīng)的改變,文獻(xiàn)報道犬AF模型中心房交感神經(jīng)再生,密度明顯增加,此外,AF時右心房交感神經(jīng)再生的程度也明顯高于左心房[6]。由此可見,AF會引起自主神經(jīng)的不均一性分布而更有利于AF的維持。
心力衰竭時心肌肥大,神經(jīng)末梢的生長速度慢于心肌的生長速度,導(dǎo)致心肌交感神經(jīng)密度降低。正常情況下,交感神經(jīng)末梢釋放的去甲腎上腺素大部分被交感神經(jīng)末梢的去甲腎上腺素轉(zhuǎn)運體uptake1再攝取,而心力衰竭時交感神經(jīng)
末梢uptake1的密度和再攝取功能下降,導(dǎo)致神經(jīng)末梢去甲腎上腺素再攝取減少[7],加上心力衰竭時交感神經(jīng)活性升高,兒茶酚胺釋放增加,導(dǎo)致心肌間質(zhì)兒茶酚胺含量增多。心力衰竭時副交感神經(jīng)的活性和生理功能均降低,對交感神經(jīng)的抑制作用減弱[8]。心臟移植后移植心臟完全失去神經(jīng)支配,對移植心臟進(jìn)行放射性核素掃描發(fā)現(xiàn),移植后1年心臟仍無神經(jīng)分布[9]。BENGEL等[10]對20例心臟移植病人行放射性核素神經(jīng)顯像發(fā)現(xiàn),移植心臟最早于術(shù)后18個月重新出現(xiàn)神經(jīng)分布,至移植后15年神經(jīng)密度仍未達(dá)到正常人水平。此外,移植心臟交感神經(jīng)按前壁、間壁、側(cè)壁、下壁的順序生長[10],提示移植心臟的神經(jīng)再生有一定時間性和空間性。影響移植后神經(jīng)再生的因素有:術(shù)后時間、供受體的年齡、術(shù)中主動脈阻斷時間和排斥反應(yīng)等[11]。病人的原發(fā)病也可能會影響移植心臟的交感神經(jīng)再生,有研究認(rèn)為缺血性心肌病比擴張性心肌病交感神經(jīng)再生提前,這可能是由于缺血性心肌病病人中高膽固醇血癥的患病率較高,而高膽固醇血癥可以明顯促進(jìn)交感神經(jīng)再生[12]。
2.1室性心律失常
美國每年有30萬~40萬人因心源性猝死(SCD)而死亡[13]。心室顫動是SCD的直接原因,而交感神經(jīng)過度激活是心室顫動的重要機制之一。研究發(fā)現(xiàn),心臟交感神經(jīng)密度和室性心律失常的發(fā)生率呈正相關(guān)[14]。用高頻電刺激刺激左側(cè)星狀神經(jīng)節(jié)[15],或?qū)GF注入心肌梗死動物左側(cè)星狀神經(jīng)節(jié)[16],均能引起心臟交感神經(jīng)再生,導(dǎo)致室性心律失常和SCD的發(fā)生率明顯升高。其機制可能為:交感神經(jīng)激活可以使兒茶酚胺釋放增多,作用于心肌α和β受體引起肌漿網(wǎng)內(nèi)鈣離子釋放增加,再經(jīng)Na+-Ca2+交換產(chǎn)生一過性內(nèi)向電流,導(dǎo)致延遲后除極,從而誘發(fā)室性心律失常;而區(qū)域性交感神經(jīng)密度的改變會增加心臟電生理的異質(zhì)性,使其更易發(fā)生室性心律失常[17]。刺激犬迷走神經(jīng)能減少心肌梗死后心室顫動的發(fā)生[18],其機制可能為:Ach與M受體結(jié)合可以抑制細(xì)胞膜L型鈣通道的開放,減少鈣離子內(nèi)流,繼而減少延遲后除極。
去交感神經(jīng)能有效治療室性心律失常。對心肌梗死合并室性心律失常的病人施行左側(cè)交感神經(jīng)節(jié)切斷術(shù),術(shù)后22個月SCD的發(fā)生率僅為3.6%,與β受體阻滯劑的療效相當(dāng)[19]。因此,對于那些不適宜服用β受體阻滯劑的心肌梗死病人,左側(cè)交感神經(jīng)節(jié)切斷術(shù)是一種良好的替代治療。也有研究用普伐他汀[20]及泊生坦[21]抑制心肌梗死后白細(xì)胞介素-1和內(nèi)皮素-1的表達(dá),使NGF表達(dá)減少,從而抑制交感神經(jīng)過度再生,減少室性心律失常的發(fā)生。
2.2AF
自主神經(jīng)對AF的觸發(fā)和維持有重要作用,研究顯示刺激交感神經(jīng)和副交感神經(jīng)均能縮短心房有效不應(yīng)期,增加不應(yīng)期的離散度,使AF更易誘發(fā)[22-23]。而異丙腎上腺素能降低Ach誘導(dǎo)AF的閾值,使Ach誘導(dǎo)的AF更容易發(fā)生和維持[24]。這些證據(jù)表明交感和副交感神經(jīng)同時激活更容易觸發(fā)AF。
射頻消融是AF治療的重要手段,在肺靜脈隔離基礎(chǔ)上增加心臟自主神經(jīng)叢消融,能有效提高消融的成功率[25],因此自主神經(jīng)消融已成為AF消融的重要策略。關(guān)于心臟自主神經(jīng)消融術(shù)后是否存在自主神經(jīng)再生問題,目前說法不一,有研究認(rèn)為自主神經(jīng)消融后不存在自主神經(jīng)再生[26],也有研究認(rèn)為射頻消融后存在心臟神經(jīng)再生并與AF的復(fù)發(fā)有關(guān)[27],但這些研究僅僅是猜測,目前尚沒有客觀證據(jù)證明自主神經(jīng)消融后存在神經(jīng)再生,并能增加AF的復(fù)發(fā)。
3.1交感神經(jīng)與心功能
交感神經(jīng)末梢釋放的遞質(zhì)為去甲腎上腺素,能夠與α和β受體結(jié)合,發(fā)揮生理作用。但去甲腎上腺素對α受體的作用要強于β受體,因而去甲腎上腺素對心肌收縮力的影響較小。有研究發(fā)現(xiàn)用利血平使心臟交感末梢去甲腎上腺素儲備耗竭,心肌收縮力未受明顯影響[28]。心臟移植后,移植心臟完全失去交感神經(jīng)支配,但病人并沒有因此而發(fā)生心力衰竭,只是心率因主要受體液調(diào)節(jié)而反應(yīng)性下降,病人運動耐量降低,而移植心臟的再神經(jīng)化則能夠提高心臟對應(yīng)激的反應(yīng),提高運動耐量[29]。由此可見,交感神經(jīng)對心臟的主要作用是提高心臟應(yīng)激狀態(tài)下的反應(yīng)性,而對心肌收縮力的影響較小。
心力衰竭時交感神經(jīng)過多釋放兒茶酚胺,導(dǎo)致心肌間質(zhì)去甲腎上腺素水平升高。過多的去甲腎上腺素則通過α、β受體引起心肌細(xì)胞肥大、凋亡,增加間質(zhì)纖維化,加劇心室重塑[30]。此外,間質(zhì)中過多的兒茶酚胺會引起β受體脫敏,使心肌對兒茶酚胺的反應(yīng)降低。動物實驗顯示,心肌組織特異性高表達(dá)uptake1,能改善交感神經(jīng)末梢對兒茶酚胺的再攝取,有助于降低間質(zhì)兒茶酚胺水平,提高β受體的數(shù)量和敏感性,改善心功能[31]。KAWAI等[32]研究顯示,ACEI類藥物能提高心力衰竭犬交感神經(jīng)末梢uptake1的密度,增加對去甲腎上腺素的再攝取,同時還能提高β受體的密度。由此可見,ACEI類藥物能夠降低心力衰竭病人遠(yuǎn)期死亡率,交感神經(jīng)末梢功能的改善可能是其重要原因之一。
3.2副交感神經(jīng)與心功能
心力衰竭時,副交感神經(jīng)對交感神經(jīng)的抑制作用減弱,主要原因有:心肺壓力感受器的異常、中樞異常、神經(jīng)末梢結(jié)構(gòu)和功能的改變等。睡眠心率作為迷走神經(jīng)的一個功能性指標(biāo)能夠預(yù)測死亡率,心肌梗死及心力衰竭病人隨睡眠心率的增加死亡率增加,如果心率下降則提示迷走神經(jīng)活性高,通常預(yù)后較好[33]。刺激迷走神經(jīng)有抗炎作用,能抑制腫瘤壞死因子α及白細(xì)胞介素-1、6、18的釋放[34],可能有助于改善心室重塑。LI等[35]在大鼠心肌梗死后慢性心力衰竭模型中,電刺激右側(cè)迷走神經(jīng)6周,使靜息心率降低到20~30 min-1,不僅血流動力學(xué)得到改善而且死亡風(fēng)險明顯降低。用一種可植入性迷走神經(jīng)刺激裝置CardioFit(BioControl Medical)刺激心力衰竭病人右側(cè)迷走神經(jīng)6個月,能改善病人心功能、生活質(zhì)量,降低左心室舒張末壓力。以上表明迷走神經(jīng)活性升高有助于改善慢性心力衰竭的預(yù)后。
心臟自主神經(jīng)和心臟疾病關(guān)系密切,自主神經(jīng)功能的變化會影響心臟疾病的進(jìn)展,而心臟疾病過程也常常伴隨著自主神經(jīng)形態(tài)和功能的改變。心肌梗死后不均一性交感神經(jīng)過度再生會造成室性心律失常和猝死的發(fā)生率升高,而增強迷走神經(jīng)的活性能減少心肌梗死后室性心律失常和猝死。交感神經(jīng)和副交感神經(jīng)在AF的觸發(fā)和維持過程中具有協(xié)同作用。心臟自主神經(jīng)對心力衰竭有重要影響,交感神經(jīng)活性增高、神經(jīng)末梢功能受損,引起間質(zhì)去甲腎上腺素增多,導(dǎo)致心肌肥大、凋亡、纖維化;而副交感神經(jīng)能通過多種機制發(fā)揮心臟保護(hù)作用,改善心力衰竭。明確心臟自主神經(jīng)與心臟的關(guān)系,有助于我們從神經(jīng)的角度理解心臟疾病的發(fā)生發(fā)展,為心臟疾病的治療提供新的思路。
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(本文編輯 厲建強)
2014-11-28;
2015-03-16
國家自然科學(xué)基金資助項目(81270215);中國博士后科學(xué)基金資助項目(2013M530664)
鄭帥(1981-),男,博士,主治醫(yī)師。
孟旭(1957-),男,碩士,主任醫(yī)師,博士生導(dǎo)師。
R541
A
1008-0341(2015)03-0374-03