Evaluating a bioprosthetic anterior mitral valve leaflet made from autologous jugular vein and expanded polytetrafluoroethylene (Gore-Tex) chordae in a sheep model

Janson, Jacques (2016-03)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The purpose of this study was to evaluate whether an autologous vein graft supported by expanded polytetrafluoroethylene (Gore-Tex) chordae can be used to replace an anterior mitral valve leaflet and whether the vein will be able to withstand the stress and strain of deformation, remain viable in the intracardiac environment and be able to adapt morphologically and grow as a valve leaflet. An autologous jugular vein graft, used as a double layer, supported by Gore-Tex chordae was used to create a functional anterior mitral valve leaflet in 21 sheep. No ring annuloplasty was used to support the annulus. The average cross-clamp time was 99 minutes (76 to 151 min) and the average bypass time was 137 minutes (109 to 188 min). One sheep died intra-operatively. The post-operative echocardiogram demonstrated laminar diastolic flow across the mitral valve with an average opening area of 2.8cm². Fourteen sheep had trace to mild mitral regurgitation (MR), 5 sheep had mild to moderate MR and 1 sheep had moderate to severe MR. The body of the vein leaflet tends to billow during systole which increases stress on the Gore-Tex chordae. Three sheep died 2 to 3 days postoperatively from mitral regurgitation due to Gore-Tex chordae that were too long, causing prolapse in 2 cases and 1 case developed a hematoma between the 2 vein layers. Seven sheep died between 1 and 6 months. Four sheep developed infective endocarditis on the mitral valve. Echocardiography at 6 months showed that the mitral regurgitation (MR) progressed with time in most of the sheep: 3 out of 11 sheep had mild MR, 5 had mild to moderate MR and 3 had moderate to severe MR. The progression of MR was due to lack of secondary chordal support of the vein leaflet and mitral annulus, leading to progressive annular dilatation, decreased leaflet coaptation length and increased tension on the primary Gore-Tex chordae. Durability of the valve should be improved by adding an annuloplasty ring and supporting the leaflet with secondary chordae. The 10 surviving sheep were euthanized between 6 to 10 months. All vein implants were examined histologically. The vein leaflet developed intimal fibroplasia and fibrous proliferation between the 2 vein layers as a response to the increased stress upon the tissue. This caused leaflet thickening, but the vein remained flexible without shortening or contracture. The 6 to 10 month vein implants showed viable endothelium and the underlying vein layers clearly showed viability with myofibroblasts, collagen and elastin. A normal healing pattern was seen at the suture lines and no calcification was seen in the vein leaflet apart from the Gore-Tex sutures. No vein growth was demonstrated. Autologous vein has the potential to be used as a valve leaflet substitute, because it remains viable in the intracardiac position for up to 10 months and is able to withstand the stress and deformation of a valve leaflet. Histologically it showed the ability to heal and to morphologically adapt to the new environment.

AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om te sien of outologiese lewendige vene weefsel, ondersteun deur politetrafluoroetileen (Gore-Tex) chordae, gebruik kan word om die anterior mitraalklepsuil te vervang. Daar wou gesien word of die vene die druk, spanning en vervorming in die mitraalklep posisie sal kan hanteer en of die vene lewensvatbaar sal bly en morfologies sal aanpas en groei. ʼn Outologiese jugulêre veen transplantaat is gebruik, as ʼn dubbel laag, ondersteun deur Gore-Tex chordae om ʼn funksionele anterior mitraalklepsuil te skep in 21 skape. Geen ring annuloplastiek is gedoen om die mitraalklep annulus te ondersteun nie. Die gemiddelde klem tyd was 99 minute en die gemiddelde kardiopulmonale omleiding tyd was 137 minute. Een skaap is intra-operatief dood. Post-operatiewe eggokardiografie het laminêre diastoliese vloei oor die mitraalklep demonstreer met ʼn gemiddelde kleparea van 2.8 cm². Veertien skape het baie geringe tot geringe mitraal inkompetensie (MI) gehad, 5 skape het gering tot matige MI getoon en 1 skaap het matig tot strawwe MI gehad. Die veenklep was geneig om uit te bult na die linker atrium tydens ventrikulêre sistolie wat spanning op die primêre Gore-Tex chordae verhoog het. Drie skape is 2 tot 3 dae post-operatief dood as gevolg van mitraal inkompetensie omdat die Gore-Tex chordae te lank was in 2 skape met veenklep prolaps en ʼn hematoom het gevorm in een klepsuil tussen die 2 veen lae. Sewe skape is dood tussen 1 tot 6 maande. Vier skape het infektiewe endokarditis op die mitraalklep ontwikkel. Eggokardiografie op 6 maande het getoon dat die mitraalinkompetensie (MI) progressief vererger het in die meeste skape met 3 uit 11 skape wat geringe MI getoon het tussen 6 en 10 maande. Die progressie van die MI was as gevolg van die verlies van sekondêre Gore-Tex chordae wat die veenklep en die mitraalklep annulus ondersteun het. Dit het gelei tot progressiewe annulus dilatasie, verminderde koaptasie lengte en verhoogde spanning op die primêre Gore-Tex chordae. Die klepfunksie behoort beter behou te word deur die veenklep te ondersteun met ʼn klepring annuloplastiek en sekondêre Gore-Tex chordae. Die 10 oorlewende skape het eutanasie ondergaan tussen 6 tot 10 maande. Alle veen klepsuile is histologies evalueer. Die veen klep het intimale fibroplasie ontwikkel met fibreuse proliferasie tussen die 2 veen lae as aanpassing tot die verhoogde drukspanning op die weefsel. Dit het verdikking van die klepsuil veroorsaak, maar die klepsuil was steeds vervormbaar sonder verkorting of kontrakture. Die 6 tot 10 maande veen oorplantings het lewensvatbare endoteel getoon en die onderliggende veen lae was lewensvatbaar met miofibroblaste, kollageen en elastien. ʼn Normale genesingsproses is gesien by die steke lyne en geen kalsifikasie is in die vene gesien nie, behalwe by van die Gore-Tex steke. Veen groei is nie gedemonstreer nie. Outologiese veen het die potensiaal om gebruik te word vir die vervanging van ʼn klepsuil, want dit bly lewensvatbaar in die hart vir tot 10 maande. Die veenklep kan die druk, spanning en vervorming van ʼn klepsuil hanteer en histologies toon die

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