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2018年5月11日 星期五

心臟外科的新紀元


心臟外科的新紀元

陳勁辰
初稿: 08/11/2008
更新: 06/22/2017

心臟外科是隨著人類科技進步最大的專科之一。內科治療無效的心臟疾病曾經一度被認為等同宣判了死刑,如今開心手術已是手術房的家常便飯而且相當安全。例如冠狀動脈繞道手術目前的手術死亡率不到5%,平均住院天數甚至可短至一週。

現代心臟外科誕生於西元195356日,John Gibbon醫師成功地修復了一名18歲女孩的心房中膈缺損(atrial septal defect),術中利用了他已研發二十年的體外心肺循環機。心臟瓣膜手術開始於西元1961年,起初人工瓣膜設計像含一顆球的鳥籠。差不多在同時,冠狀動脈繞道手術也逐漸風行起來。對不可逆之末期心衰竭之外科治療,心臟移植自1970年代開始嘗試,於1980年代環孢靈( cyclosporine)引進才真正成功。另一方面,美國衛生研究院(National Institutes of Health)1964年開始人工心臟研究計畫以來,各種機械循環輔助也被發展出來。近十年來,我們也目睹了首例成功的人工心臟長期使用。微創(minimally invasive)手術方法也被應用在各種不同術式。不停跳(beating-heart)或免心肺機(off-pump) 冠狀動脈繞道手術逐漸成為主流。接下來為各位介紹各個次領域的現況。

自從四十年前首例冠狀動脈繞道手術成功以來,冠狀動脈疾病的病理和治療都有長足的進步。從對動脈粥狀硬化的了解,到近年來內科的冠狀動脈支架或氣球擴張術,及外科的免心肺機冠狀動脈繞道手術。 1970年代對內科及外科治療方法的比較,我們發現外科繞道手術對較嚴重病人有較佳的長期存活率,例如左主動脈疾病(left main disease),或顯著之二或三條血管疾病併左心室功能不良。 另外使用左內乳動脈(left internal mammary artery)接左前降動脈(left anterior descending artery),及充分的血管繞道(complete revascularization),都可大幅改善長期存活。以十年暢通率而言,左內乳動脈有90%,隱靜脈則只有50%左右。 另外由於內科心導管治療的風行,接受手術的都是剩下較嚴重的病人,還好因為手術及加護病房技術的進步,冠狀動脈繞道手術的死亡率仍可維持在3%左右。 免心肺機冠狀動脈繞道術(off-pump coronary bypassingOPCAB)是近十年來的一個大轉變,它避免了體外循環潛在的不良影響,例如全身發炎反應(systemic inflammatory response)及微栓塞(micro-embolism)腦傷。許多研究發現,這種術式可能會降低輸血量,縮短住院天數,及減少醫療成本。在技術方面,由於要在心搏下翻動心臟,手術中需要外科醫師及麻醉科醫師的合作無間。器械方面主要是使用固定器把心臟和把血管接合處定位,已利顯微接合,目前常用的有MedtronicOctopusGuidantAcrobat系統。另外縫合切洞的手術視野維持,可用分流管(intra-coronary shunts)或拉帶(sling)控制血流。目前只要外科醫師經驗足夠,且病人適合,進行冠狀動脈繞道手術可以不用心肺機體外循環。

在西元1960年,Harken醫師和Starr醫師分別植入了首例人造主動脈瓣和二尖瓣,自此開創了心臟瓣膜手術的新紀元。首先談談人工瓣膜疾病(prosthetic valve disease),這是接受新瓣膜植入之病人多多少少會遇到的問題。這包括血栓栓塞(thromboembolism),抗凝血劑相關出血(anticoagulant-related hemorrhage),人工瓣膜心內膜炎(prosthetic valve endocarditis),結構性瓣膜破壞(structural valve deterioration),及病人-瓣膜不合(patient-prosthesis mismatch)CoumadinAspirin是用來抗凝血最常用的藥物,要防止血栓又要避免出血,亞洲人一般是將PTINR控制在1.52倍左右。心內膜炎在術後三個月內發生率最高,要避免心內膜炎,一定要嚴格遵守預防性抗生素的使用,例如牙科治療的時候。目前科技還沒有辦法造出和人體原來瓣膜一樣耐用的瓣膜,因此人工瓣膜結構會隨時間被破壞,尤其是生物組織瓣膜一般只能用十年左右。人工瓣膜的血行動力學多少不儘完美,在人工瓣膜對病人相對較小時可能會因阻力而產生顯著的壓力差,而發生病人-瓣膜不合的現象,這常發生在主動脈根部較小的病人身上,解決之道是選擇血行動力學更有效率的瓣膜,或將主動脈根部環增大而使用較大的瓣膜。瓣膜手術開刀時機要適當的選擇,但通常是在有症狀出現或不可逆心臟衰竭出現之前,心臟超音波是最好的檢查工具。第一個被廣為使用的機械瓣膜是由塑膠和金屬做的,原型是Starr-Edwards瓣膜,狀似裝球的鳥籠。經多年改良克服種種問題後,瓣膜變成較扁平,球變成圓盤,一個或分成兩半,靠關節活動。材質也改良成pyrolitic carbon,外觀似金屬而非金屬,無導磁性而對磁核共振掃描沒有問題。常見的有St JudeMedtronic Hall,及Carbomedics瓣膜。他們有優良的血行動力學,非常耐用,唯一的缺點是需要服用抗凝血劑。生物瓣膜是由動物組織做成的。原型是豬的主動脈瓣膜,經化學處理以增加耐用性,再架在塑膠框架上。它的化學處理去除了免疫性故不會排斥。抗凝血劑Coumadin只需在術後前三個月使用,之後Aspirin即足夠。目前常用的有Carpentier-EdwardsHancock豬瓣膜。生物瓣膜的缺點是耐用性,磨損和鈣化約在十年後會開始影響結構功能,故它都用在七十歲以上之病人。新的研發主要在增長它的耐用性,例如新的化學固定方法或抗鈣化處理,或使用別的生物組織,例如牛心包膜製成的Carpentier-Edwards Perimount瓣膜,耐用性增長五年,故可用在六十五歲病人。因為生物瓣膜的血行動力學沒有機械瓣膜好,病人-瓣膜不合是個潛在問題。新一代的生物瓣膜號稱有更佳的血行動力學表現,叫做無支架”(stentless)辦膜。它是把豬的主動脈瓣連同支持的主動脈管壁一同取下,再經特殊化學處理,有些型式會在主動脈管壁外層覆以布料。短期研究顯示它的壓力差極低,而耐用性與傳統生物瓣膜類似,長期研究尚待結果。常見的有Toronto Stentless Porcine瓣膜及Medtronic Freestyle瓣膜。其他的瓣膜選擇還有人體瓣膜(homograft)和自體瓣膜(autograft) 人體瓣膜是自剛死亡的人取出。 自體瓣膜是將病人自己的肺動脈瓣轉植到主動脈瓣位置,這種術式叫做”Ross手術,因為自己的瓣膜還會長大,故這常用在小孩子身上。在二尖瓣手術方面,於西元1925年,Souttar醫師首先在心臟跳動下,將手指插入一閉鎖的二尖辦而打開之,解決了二尖辦閉鎖的問題。之後心肺機體外循環的使用,使得心臟能停止跳動而打開,二尖瓣可再直視下做仔細修補。在1970年代,Carpentier醫師提出許多修補二尖瓣閉鎖不全的手術技巧,他的技巧可修復約70%閉鎖不全的二尖瓣。 二尖瓣修補可避免之前提過的人工瓣膜疾病,且不用抗凝血劑。但修補的耐用性則多仰賴外科醫師的技術,二尖瓣疾病可能會隨時間過去而復發,而使得二尖瓣人工瓣膜置換無可避免。心臟傳導阻礙是瓣膜手術常見的併發症,因為傳導系統剛好經過主動脈瓣,二尖瓣,及三尖瓣附近。手術死亡率在主動脈瓣置換是4%,二尖瓣置換是6%,主動脈瓣置換併冠狀動脈繞道是7%,二尖瓣置換併冠狀動脈繞道則高達11%。未來瓣膜手術的發展將包含兩個方向:微創技術(minimal access),及組織工程。微創技術利用較小的傷口,攝影機協助,甚至機器人科技,朝向減少術後疼痛及住院天數努力。組織工程,例如SynerGraft,則嘗試將生物瓣膜中的細胞完全移除,則結締組織可作為基質骨架,植入病人體內後,病人細胞長在此基質上而形成與原有瓣膜相去不遠的心瓣膜,達成完美瓣膜的夢想!

小兒先天性心臟病在近年來的進展主要在兩方面: 自體肺動脈瓣轉植置換主動脈瓣(Ross手術)的增加; 複雜單一心室重建的進步,包括左心發育不全症候群(hypoplastic left heart syndrome),這使得存活率顯著改善。在小孩及青少年的主動脈瓣置換,採用Ross手術有明顯的優點。 自體瓣膜在十年後只有3%有功能退化,屍體瓣膜有20%,動物瓣膜則高達70%。機械瓣膜理論上不會有功能退化,但它需要終生服用抗凝血劑,且不會隨病人長大,瓣膜相對過小時會有壓力差的增加。複雜單一心室異常治療的進步在於階段性手術的採用,使得長期存活率甚至可高達90%。單一心室最好負擔體循環,肺循環則自體循環被動地引至肺動脈到肺氧合,此時肺動脈壓不可太高,否則會體靜脈高壓及肺氧合不足,Fontan醫師提出這個理論並應用在病人身上,但成果不佳,原因是因為單一手術的血行動力學變化太大。數年來對原來Fontan手術有多種修正,其中目前廣為採用的是階段性手術。第一階段先連接上腔靜脈及右肺動脈,使血流能至雙側肺部,即雙向Glenn分流(bi-directional Glenn shunt)。第二階段則連接下腔靜脈及肺動脈,使體循環靜脈回流全部經肺動脈至肺氧合,完成修正式Fontan循環或完全腔靜脈肺動脈連接(total cavopulmonary connection) 這第二階段有多種小修正,例如在心房中膈開窗或在下腔靜脈及肺動脈連接管道與右心房間開窗,這可解除因肺高壓所致的體循環靜脈高壓,減少腹水及肋膜腔積水的發生。下腔靜脈及肺動脈連接管道可放在心房內也可放在心臟外。病人選擇對於手術成功很重要,必須有低肺血管阻力,低肺動脈壓力,無肺動脈狹窄,及單一心室功能良好。房室瓣膜逆流或主動脈下阻塞都會減少成功率。 左心發育不全症候群近年來手術成效大有進步,主要是階段性手術觀念的功勞。這疾病不只左心室發育不全,主動脈瓣,昇主動脈,主動脈弓都發育不全。 左心發育不全症候群在數個月內就會致命。早期的手術成效很差,死亡率可高達八成。 直到近年來Norwood階段性手術才扭轉情勢。這是把主肺動脈與左右肺動脈分開,將它連接整型擴大後的主動脈。 肺循環再從体肺循環分流( systemic-pulmonary shunt) 而來,例如Blalock-Taussig分流。 心房中膈再打窗,使左心房的肺靜脈回流可到右心房去,再到右心室去供應體循環。接下來就是進入Fontan的方法。下一階段是雙向Glenn分流,在小孩約六個月大時進行,第三階段則是建立Fontan循環,在一至二歲時進行。起初Norwood醫師採用此法可得五成的存活率。近年來的進步使得存活率在某些醫學中心甚至可達八至九成。心臟移植還是左心發育不全症的另一治療選擇,存活率與Norwood方法差不多。雖然可獲得正常雙心室的心臟,移植帶來新的問題,像排斥、感染、或移植後冠狀動脈疾病,都會影響長期存活。兩者孰佳,仍有爭議。

機械循環支持(mechanical circulatory supports)是處理嚴重心衰竭相當重要的工具,尤其是藥物無效之時。它常見的形式包括葉克膜(ECMOextracorporeal membrane oxygenation),心室輔助器(VADventricular assist device,例如HeartMate-IIHeartMate-3、或HeartWare),廣義上也包括主動脈內氣球幫浦(IABPintra-aortic balloon pumping)。另外最新的有全人工心臟(total artificial heart),像SynCardia 它們的使用時機有四: 急性心肌梗塞引起的心因性休克,手術後心肌衰竭,心肌炎引起之急性心衰竭,及慢性心衰竭的突然惡化。治療目標有三; 過渡至移植(bridge to transplantation),過渡至恢復(bridge to recovery),及終極治療(destination therapy) 機械循環支持可以短期支持病人至心臟功能自急性衰竭恢復或下一步治療奏效為止(ECMO,體外膜氧化器,或稱葉克膜),或中長期支持至慢性穩定或心臟移植可得(LVAD,左心室輔助器)。今年一月新英格蘭醫學期刊(NEJM)發表REMATCH研究的結果,發現左心室輔助器HeartMate比純用藥物治療在一年左右更能給心衰竭病人較佳的存活優勢和生活品質。葉克膜裝置過程快速,適用於大人或小孩,但不能長期使用。Thoratec心室輔助器可支持左或右心室,也可用在體型較小的病人。HeartMate心室輔助器的病人活動性較佳,但植入腔較易感染。其他心室輔助器還有HeartWare等,原理可以是軸流幫浦(axial-flow pump),或離心幫浦(centrifugal pump)。一般而言,裝置的選擇要考慮病人的情況,及醫師的熟悉度。在準備長期使用的情況下,心室輔助器HeartMate-II是我們目前較常使用的選擇。

機器人微創心臟手術(robotics minimally invasive cardiac surgery)將使心臟外科進入新的領域,手術傷口變小,而且病人術後恢復快。且藉由機器人手臂的幫助,外科醫師可進行更精細的操作。這不是神話,西元19991122日,加拿大London Health Sciences CentreBoyd醫師使用Zeus機器人系統成功地完成首例機器人微創冠狀動脈繞道手術。目前這個領域主要是廠商Intuitive Surgical (http://www.intuitivesurgical.com) 。其產品有手術機器人手da Vinci 系統。價格均需約一百萬美金以上。機器人科技在心臟外科的應用已愈來愈多人嘗試,西元199912月,美國Penn State College of Medicine Damiano醫師也成功在美國本土用Zeus完成首例機器人微創冠狀動脈繞道手術。西元20001月,歐洲也發表多例利用da Vinci成功完成內視鏡冠狀動脈繞道手術(TECABtotal endoscopic coronary artery bypass)。西元20003月,法國L'Institut Mutualiste Montsouris ChiosyLaborde醫師利用Zeus成功地完成開放性動脈導管(patent ductus arteriosus)的內視鏡結紮手術,這是小兒心臟外科的首例應用。目前全球(包括台灣)皆可常規使用da Vinci進行微創心臟瓣膜手術。在全世界機器人手術展開臨床試驗之時,美國食物藥品管理局(FDA)要完全核准之一個重要因素是硬體之安全性及軟體的可靠性。

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Robotics-assisted cardiac surgery
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  3. Leilyn Perri,Robots usher in New Era in Heart Surgery,Penn State Medicine,2000 http://www.collmed.psu.edu/PS_Medicine/winter00/robots.htm (Damanio's on TV),4/20/00 Compuer Motion 
  4. Colleen Anderson,Robotic Heart Surgery,Technocopia,11/24/99 http://www.technocopia.com/health-19991124-roboheart.html,4/22/00
  5. http://www.hoise.com/vmw/articles/LV-VM-03-98-5.html 
  6. Computer Motion and U.S. Surgical Form strategic alliance to Jointly Develop Instruments for Robotic Heart Surgery,Developing Instruments For Robotic Heart Surgery Announced,12/28/99 http://204.180.41.224/BBoard/Forum11/HTML/000115.html ,4/23/00
  7. Theresa Tamkins,Robotic Arms Assist Heart Surgery,Reuters Health Information,12/09/99 http://www.heartinfo.org/reutersnews/t120915f.htm ,4/18/00
  8. Wendy Wifler,The Future is Now,Computer Motion,10/4/99 http://www.medtechinvestor.com/new_page_5.htm ,4/20/00
  9. Yahoo Buisness Page,http://biz.yahoo.com/n/r/rbot.html (company news),4/21/00
  10. Computer Motion Inc.,Quarterly Report,Quotes Page,11/12/99 http://biz.yahoo.com/e/991112/rbot.html (company in trouble),4/21/00
  11. Computer Motion,Press Release,Yahoo Finance Page,3/30/00 http://biz.yahoo.com/bw/000330/ca_compute_1.html ,4/20/00
  12. Warren King,Using Robotics to mend broken Hearts,Seattle Times,4/13/99 http://www.seattletimes.com/news/health-science/html98/robo_19990413.html ,4/24/00
  13. Robert Davis,Robot wields heart surgery scalpel,USA Today,11/23/99 http://www.usatoday.com/life/cyber/tech/review/crg433.htm,4/18/00 
  14. Michael J. Martinez,Hands of da Vinci,ABC News,1999 http://more.abcnews.go.com/sections/tech/CuttingEdge/cuttingedge990730.html ,4/20/2000
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  16. Hershey Patients Doing Well,MDNetwork,6/99 http://www.psghs.edu/community_information/md_network/jul_99/hershey.htm (4/40/00)
  17. Julie Stevens,Giving Surgeons a Helping Hand,Mercury Center,4/18/00 http://www.mercurycenter.com/archives/reprints/0400/Sevrens04182000.htm,4/27/00
  18. Robotics,FDA,2000 http://www.verity.fda.gov/,4/23/00
Congenital heart disease
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