Ann Thorac Surg 2005;79:1465
© 2005 The Society of Thoracic Surgeons
Correspondence
Endothelialization and Functional Neointima on Vascular Grafts in Humans
Yasuko Tomizawa, MD
* Department of Cardiovascular Surgery, The Heart Institute of Japan, Tokyo Women's Medical University, 8–1 Kawada, Shinjuku 162–8868, Tokyo, Japan
(E-mail: 4crnry{at}hij.twmu.ac.jp).
To the Editor:
The article by Walles and colleagues [1] demonstrated neointimal functionality of vascular grafts explanted from left ventricular assist device (LVAD) systems. The provocative findings of Walles and colleagues [1] raise some important concerns.
Endothelial cells lining the lumen of a vascular graft usually form a single layer, whereas the authors observed multilayer immunohistologically in the outflow conduit and showed it in figure 1 of their article. Although the luminal coverage of the inflow conduit was described as neointima, it seems to be fibrin adhesion, because the authors mentioned that adherence was loose by macroscopical observation. Immunohistological staining of CD31 and factor VIII by themselves are not sufficient to confirm the identity of endothelial cells. After observing the morphologic characteristics of endothelial cells, these immunohistological stainings then become important as supporting data. Judging from the evaluation of endothelialization described by the authors, the proof of identity of endothelial cells seems inadequate and more histopathological evidence based on a specialist's report is required to support endothelialization.
From the 1950s, it is well known that the morphology of endothelial cells on an artificial material is different compared with those on a native vessel [2]. The authors mentioned that this study was planned to examine the process of reendothelialization of synthetic vascular grafts in humans, whereas many studies have already been done to examine endothelialization on vascular grafts in humans, and it has been recognized that endothelialization is slow due to luminal thrombus [3] and is limited to an artificial blood vessel in humans.
The fabric vascular grafts from the HeartMate LVAD systems (Thermo Cardiosystems Inc, Woburn, MA), which the authors evaluated as Dacron grafts (grafts made from Dacron polyester fibers, DuPont, Wilmington, DE), are usually coated with a chemically treated biological material such as formalin cross-linked collagen. The influence of the biological coating material on vascular grafts is important after implantation, due to slow absorption and endotoxin [4]. In the current study, endothelialization of the implanted vascular grafts 9 months after implantation was delayed, and the major cause is possibly inflammation due to the coating material and the minor cause being the Dacron grafts themselves. Foreign body reaction, which could be a cause of delayed healing, was not described in this article. Furthermore, measurement of endothelialized area or percentage of the area occupied by endothelial cells was not mentioned before investigating neointimal functionality with the latest evaluation method.
The authors concluded that "Dacron is not suitable as scaffold," whereas they have not directly proven that Dacron was not satisfactory as scaffold. Even using the same original polyester yarn "Dacron" from DuPont Company, the biocompatibility of the manufactured products, such as vascular grafts from different companies is completely different due to residual chemicals, graft structure (knitted versus woven), and arrangement and processing before implantation. Cell affinity was better in grafts with ultrafine polyester fibers [5], and the autologous fragmented tissue implantation method accelerated endothelialization with endogenous cytokines in commercially available polyester vascular grafts [6]. The authors used the latest and sophisticated methods to evaluate functional neointima; however, they should be careful about evaluating the basic characteristics of endothelial cells.
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References
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- Walles T, Görler H, Puschmann C, Mertsching H. Functional neointima characterization of vascular prostheses in human Ann Thorac Surg 2004;77:864-868.[Abstract/Free Full Text]
- Meijne N. Endothelial growth after use of vascular nylon transplants Ned Tschr Geneesk 1958;102:1772-1774.
- Noishiki Y, Tomizawa Y, Yamane Y, Matsumoto A. The vicious cycle of nonhealing neointima in fabric vascular prostheses Artif Organs 1995;19:7-16.[Medline]
- Yamamoto K, Noishiki Y, Mo M, Kondo J, Matsumoto A. Unusual inflammatory responses around a collagen-impregnated vascular prosthesis Artif Organs 1993;17:1010-1016.[Medline]
- Niu S, Satoh S, Shirakata S, et al. Development of ultrafine polyester fiber vascular grafts with high endothelialization capabilityAngiogenesis by ultrafine polyester fibers. ASAIO Trans 1989;35:202-205.[Medline]
- Noishiki Y, Yamane Y, Tomizawa Y, et al. Rapid endothelialization of vascular prostheses by seeding autologous venous tissue fragments J Thorac Cardiovasc Surg 1992;104:770-778.[Abstract]
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