Polytetrafluoroethylene leaflet extensions for aortic valve repair

Abstract

In this issue of EJCTS, Nosal et al. [1] have published their initial experience with polytetrafluoroethylene (PTFE) leaflet extensions for aortic valve (AV) repair in congenital patients. Although this is a small series, the authors must be congratulated on their excellent results. The main objective in AV repair is to restore the matching between the quantity of cusp tissue and the valve orifice in order to achieve good and durable coaptation. To avoid recurrence of aortic insufficiency (AI) and/or stenosis after AV repair, a systematic surgical approach determined by leaflet as well as aortic disease (the functional aortic unit—FAA) must be adhered to [2]. In pure AI, due to the dilatation of the FAA, generally there is enough tissue to achieve this goal without addition of tissue. Hence, one should be cautious in applying leaflet extensions liberally to situations where there is sufficient quantity of cusp tissue. However, in paediatric population, rheumatic valves and in some cases of endocarditis, our goal is accomplished by adding tissue to reconstruct the valve. Leaflet extensions are likely to be required in asymmetric (type 1) restrictive bicuspid valves where management of the restrictive raphe is a key component of leaflet repair [3]. This paper is of great interest in the above group of patients where the search for the ideal material continues. Leaflet extensions (autologous pericardium [fresh, glutaraldehyde-treated], bovine pericardium, fascia lata, duramater, etc.) have been used for a long time for AV repair. Although used at other sites in the heart, the use of PTFE for AV repair has not been reported. Moreover, the thickness of the PTFE extension used by the authors is much less when compared with a similar extension used in the mitral position. This may ensure greater pliability and possibly a lesser thrombogenic risk. Technically speaking, any patch material could be used to perform AV repair. However, maintenance of AV leaflet coaptation requires adequate mobility in a high-pressure area over a longer period of time. PTFE is a durable monofilament plastic polymer that has unique physical characteristics including greater flexibility, remarkable breaking strength, negative charge like native endothelium and biostability. However, the issues of structural degeneration, calcification, thrombogenecity and infection should be borne in mind to ensure long-term durability of valve repair. There is little published information concerning natural tissue responses to long-term use of PTFE grafts in humans. In a recent study on explanted cardiovascular PTFE grafts [4], the authors found that interstitial calcification was associated with graft disruption which may play a role in eventual graft failure. Hayabuchi et al. [5] reported that most of the patients with surgically repaired congenital heart disease displayed evidence of calcification in PTFE cardiac grafts with multidetector computed tomography. Dystrophic calcification with fracture/rupture of PTFE sutures has also been noted to cause recurrent mitral insufficiency in patients with long-term indwelling neochordae [6]. In an experimental study performed in an animal model, PTFE valves were inserted in the tricuspid position [7]. In half of the patients, the leaflets were stiffened and also showed thrombosis, margin eversion and mineralization. Gross calcification always involved the commissural areas. Another promising option is tissue engineering where de novo living tissue is fabricated to replace diseased AVs. The new valve designed from a living cellular component facilitates biological integration, adaptation, remodelling and growth [8]. This process has enormous potential for the future management of young patients with AV disease requiring valve growth while avoiding the valve-related complications of current non-living prosthetics. Although a promising option, whether PTFE leaflet extensions for AV repair are reliable in the long term remains to be seen. Imaging studies may help predict which grafts are predisposed to failure by calcification. More studies are undoubtedly required to understand the progression and consequences of PTFE degeneration which may lead to therapies to prevent re-interventions after AV repair with PTFE leaflet extensions.