AKT Chau

Abstract

Vascular stenoses and hypoplasia in children are often associated with congenital heart disease or occur as a residual lesion or complications after surgical repair. Among these lesions, branch pulmonary artery stenoses are the commonest, other lesions include coarctation of aorta, stenosis of systemic veins after Fontan repairs, post-operative pulmonary venous stenosis, aortopulmonary collateral artery or shunt stenosis and post-operative conduit stenosis. They are usually associated with significant mortality or morbidity if untreated. Conventional surgical repair for these vascular stenoses may be difficult, carries a high operative risk or is associated with disappointing outcome. Some of the lesions may even be surgically inaccessible. Balloon angioplasties may be effective in relieving obstruction in some of these lesions. It can achieve successful dilation in about 60% of branch pulmonary arterial stenoses but the success rate may be lower in other lesions. Furthermore, the effects of balloon angioplasties in many lesions are often temporary and restenosis as a result of elastic recoil or subsequent scarring and fibrosis is common. Implantation of a stent provides a firm support and maintain patency of the vessels after balloon dilatation. Both balloon-expandable and self-expanding stents have been used to treat various vascular stenoses but available evidence suggests that the former is more suitable for use in children as it can be redilated to a higher diameter to keep pace with growth and is associated with fewer complications. The clinical application of stent implantation to treat various vascular stenoses and congenital heart diseases has been continuously widened since the late 1980s. It has replaced surgery as the treatment of choice in branch pulmonary arterial stenoses, post-surgical recoarctation of aorta that are unresponsive to balloon angioplasty, systemic venous obstruction and systemic venous baffle obstruction in Mustard or Senning operations. In native coarctation beyond young infancy, stenting is increasingly accepted as a primary treatment in adolescence and adults to avoid the higher surgical risks in this group of patients. In young children who do not respond to primary balloon angioplasty for native coarctation, stent implantation has also become an accepted treatment provided a stent that allows redilation to the adult aortic diameter is used. Stent implantation in conduit stenosis can prolong the life span of the conduit and delay the time of reoperation. In complex heart diseases where there is aortopulmonary shunt or aortopulmonary collateral artery stenoses, stent implantation serves as an effective alternative to surgical treatment. Stenting of the arterial duct has been increasingly incorporated into the management strategy of complex pulmonary atresias and hypoplastic left heart syndrome. Transcatheter approach using stents to complete the Fontan palliation may avoid multiple operations in patients with univentricular heart. Percutaneous pulmonary and aortic valve implantation to treat the respective valvar regurgitations are innovative new applications of stent that have gained initial success. Although the medium to long-term outcomes after stent implantation of most of the vascular stenoses are promising, restenosis caused by intimal hyperplasia and growth remains a long-term concern but it can be treated effectively and safely by stent redilation. New stent design is expected to overcome the limitations of the present stents and further widen its scope of application. Stent implantation is a new therapeutic modality that has added to the armamentarium of the paediatric cardiologists and cardiac surgeons in treating congenital heart disease.

兒童患血管狹窄或血管發育不良多與先天性心臟病的發生相關，或是由於外科手術後遺留的病狀，或由手術併發症所造成的。在所有的有關病例中，肺動脈狹窄最常見，其次包括主動脈弓狹窄， Fontan 修補術後周邊靜脈狹窄，術後肺靜脈狹窄，主─肺動脈交通支，分流支血管以及術後心胸導管狹窄。通常如未能及時解決血管的狹窄問題會使病情加重，甚者導致死亡。以常規外科手術解決血管狹窄問題比較困難，其手術風險高，通常收不到預期的治療效果。某些部位的狹窄以外科手術根本無法進行。球囊血管成形術可有效地解除部份狹窄所引起的血管阻塞。對於肺動脈狹窄而言，球囊擴張的成功率大約 60%。但其他血管狹窄擴張率則較低。但是，球囊擴張術只可以暫時地解除狹窄，由於血管的彈性回縮，繼發性疤痕形成，纖維化所造成的再狹窄卻經常發生。如果在球囊擴張術後置入血管支架，就可以給予血管實質性的支持，以保証球囊擴張術的效果。目前臨床上使用的兩種支架，一種是球囊加壓擴張型，另一種是自動膨脹式，二者都可用來治療各種類型的血管狹窄。據結果顯示，兒童病患適合使用前一種支架。因為其可以再加壓擴張至更大直徑以適應兒童生長的需要。自 80 年代末期以來，臨床上不斷擴大支架的使用範圍，包括治療多種類型的血管狹窄。部份病例的治療首選球囊擴張，及支架置入，已取代了外科手術。這些病例包括肺動脈狹窄，主動脈弓術後再狹窄，周邊靜脈血管狹窄，或在 Mustard 及 Senning手術後出現的周邊靜脈血管的隔膜式阻塞。目前對於年幼的先天性主動脈弓狹窄嬰幼兒，也愈來愈趨向於同青少年或成年患者一樣首選置入支架為基本治療方法，因為對這一組病人來說，此治療方法可以減低手術風險。對於那些初次採用球囊擴張術失敗的嬰幼兒也建議使用支架置入方法，因為這些支架可以再行擴張，甚至可以擴張至成人主動脈的大小。心胸導管狹窄置入支架後可以延長心胸導管的使用壽命，推遲再手術的時間。對於複雜的先天性心臟病，如主─肺動脈分流，主─肺動脈交通側支狹窄，除外科手術外，也可以選擇另一個有效的支架置入治療法。治療複雜的肺動脈閉鎖及左心室發育不良綜合症，可以用支架擴張支撐動脈導管，達到分流作用。單心室患兒 Fontan 的最後治療步驟也可以經心導管置入支架來完成，以減少手術的次數。經皮置入帶有支架的肺動脈或主動脈瓣膜治療瓣膜反流是一個新的嘗試，已獲得初步成效。大多數血管狹窄患兒置入支架後的中期及長期結果顯示：置入初期，支架刺激作用使血管內膜過度增生，造成血管再狹窄，這一問題仍需長期關注，但由於支架可以再擴張來解決狹窄，所以這一方法仍是有效而安全的。對於新的支架設計的期望是克服現有產品的局限性，進一步擴廣使用適應症範圍。支架置入是一種新的治療手段，已成為兒科心臟病專家及心臟外科醫生治療先天性心臟病的方法之一。