早期无支架二尖瓣替换术后的主要并发症是腱索断裂，腱索断裂后导致二尖瓣严重关闭不全。为了防止腱索断裂，Vetter等〔7〕使用2对人工腱索(ePTFE，膨体聚四氟乙烯)加固二尖瓣前叶。但天然腱索在高负荷情况下可延长10%～15%，而ePTFE在高张力下总长度变化＜2%，另外ePTFE有撊涠詳(creep)现象，天然腱索则没有这种现象〔21〕。ePTFE是目前临床使用较多人工腱索材料〔22，23〕，植入体内后其表面光滑，没有血栓形成和钙化，并有内皮细胞覆盖，以ePTFE为支架可形成新生腱索〔23〕。Kobayashi等〔24〕根据心脏超声心动图检查结果证实，术后人工腱索ePTFE优于异种心包。
结束语
虽然临床及动物实验应用无支架生物二尖瓣结果表明：在开瓣压、开口面积、维持左心室功能等血液动力学方面显示其优良特性，但是随访时间短，病人例数少，其远期结果有待进一步观察。耐久性差是所有生物瓣的致命弱点，提高生物瓣的耐久性是生物瓣研制的根本方向。
作者单位：100037 中国医学科学院
参考文献
1 Pansini S,Summa MD,Galloni M,et al.Morphological comparison of mitral and aortic bioprostheses explanted from the same patient for primary tissue failure.J Cardiovasc Surg,1996,37:291-294.
2 Haziza F,Papouin G,Barratt-Boyes B,et al.Tears in bioprosthetic heart valve leaflets without calcific degeneration.J Heart Valve Dis,1996,5:35-39.
3 Robicsek F.Homograft replacement of the atrioventricular valves.J Heart Valve Dis,1996,5:607-622.
4 Acar C,Tolan M,Berrebi A,et al.Homograft replacement of the mitral valve:graft selection,technique of implantation,and results in forty-three patients.J Thorac Cardiovasc Surg,1996,111:367-380.
5 Ozdogan ME,Oktar L,Gunaydin S,et al.Mitral and aortic valve replacement using fresh unstented pulmonary and aortic homografts.J Heart Valve Dis,1996,5:181-185.
6 Renzulli A,Cerasuolo F,Festa M,et al.Stentless fresh pulmonary homograft in mitral position.Tex Heart Inst J,1995,22:301-303.
7 Vetter H,Nerlich A,Welsch U,et al.Total replacement of the mitral apparatus with a stentless,chordally supported mitral valve allograft:an experimental study.J Thorac Cardiovasc Surg,1996,111:595-604.
8 Vrandecic MOP,Fantini FA,Gontijo BF,et al.Surgical technique of implanting the stentless porcine mitral valve.Ann Thorac Surg,1995,60:s439-442.
9 Deac RFP,Simionescu D,Deac D.New evolution in mitral physiology and surgery:mitral stentless pericardial valve.Ann Thorac Surg,1995,60:s433-438.
10 Liao K,Wu JJ,Frater RWM.Intraoperative epicardial echo/doppler evaluation of a stentless,chordally supported quadricusp mitral bioprosthesis.ASAIO,1993,39:M634-638.
11 Shinoka T,Breuer CK,Tanel RE,et al.Tissue engineering heart valves:valve leaflet replacement study in a lamb model.Ann Thorac Surg,1995,60:s513-516.
12 Shinoka T,Ma PX,Shum-Tim D,et al.Tissue-engineered heart valves:autologous valve leaflet replacement study in a lamb model.Circulation,1996,94(Suppl II):II164-168.
13 Shum-Tim D,Ma PX,Langer R,et al.Tissue-engineered valve leaflets:does cell origin affect outcome(Abstract)?Circulation,1996,94(Suppl I):I73.
14 Komeda M,Glasson JR,Bolger AF,et al.Papillary muscle-left ventricular wall?/FONT＞complex?/FONT＞.J Thorac Cardiovasc Surg,1997,113:292-301.
15 Castro LJ,Moon MR,Rayhill SC,et al.Annuloplasty with flexible or rigid ring does not alter left ventricular systolic performance,energetics,or ventricular-arterial coupling in conscious,closed-chest dogs.J Thorac Cardiovasc Surg,1993,105:643-659.
16 Glasson JR,Komeda M,Daughters GT,et al.Three-dimensional regional dynamics of the normal mitral anulus during left ventricular injection.J Thorac Cardiovasc Surg,1996,111:574-585.
17 Glasson JR,Komeda M,Daughters GT,et al.Loss of three-dimensional canine mitral annuluar systolic contraction with reduced left ventricular volumes.Circulation,1996,94(Suppl II):II152-158.
18 Ramsheyi SA,Pargaonkar S,Lassau JP,et al.Morphologic classification of the mitral papillary muscles.J Heart Valve Dis,1996,5:472-476.
19 Komeda M,DeAnda A,Glasson JR,et al.Improving methods of chordal-sparing mitral valve replacement.Part II:Optimal tension for chordal resuspension.J Heart Valve Dis,1996,5:477-483.
20 Komeda M,DeAnda A,Glasson JR,et al.Improving methods of chordal-sparing mitral valve replacement.Part III:Optimal direction for artificial chordal.J Heart Valve
