Neointimal hyperplasia, vein graft remodeling, and long-term patency

Neointimal hyperplasia is generally considered as the major cause of vein graft stenosis and is the leading pathological sign of vein graft disease. Most research on this problem has focused on the inhibition of neointimal growth, based on the hypothesis that the inhibition of neointimal hyperplasia would improve long-term patency of the vein graft. However, the inhibition of cell proliferation-mediated early neointima accumulation does not translate into clinical benefits (5). In small animal models, neointimal hyperplasia is an early event lasting as long as several weeks after vein graft implantation (9). There is no direct scientific evidence showing that an early inhibition of neointimal hyperplasia will result in improving long-term patency. Neointimal formation is also regarded as a pathophysiological adaptation to increased cyclic intramural tension. Moreover, as stenosis is defined as a +50% reduction in luminal diameter (2), the neointima established in many vein graft animal models does not result in a significant loss of luminal area. In the clinic, long-term (up to 15 years) and progressive vein graft disease is of much more concern compared with the acute neointimal hyperplasia that usually occurs within one year (1).