Scanning electron microscopic analysis of vessel wall reactions after coronary stenting

High restenosis rates are still a major factor limiting the use of minimal invasive coronary stenting. Tissue reactions to the implanted alloplastic e ndoprostheses are still barely understood. 18 coronary artery segments 32 h ours up to 340 days after stent implantation of 16 patients were post-morte m investigated. The pathomorphological findings of the vessel wall after st ent insertion were studied by scanning electron microscopy (SEM). Stent int egration can be divided with intraindividual differences in three phases: I n the acute phase (< 6 weeks) the border between vascular lumen and arteria l wall is constituted by a thin, multi-layered thrombus. During the time co urse of integration, increasing amounts of Smooth Muscle Cells (SMC) and ex tracellular matrix can be detected. No endothelial cells can be found in th e implantation zone. In the intermediate phase (6 weeks to 12 weeks) the ne ointima consists of extracellular matrix and increasing numbers of SMC. The borderline between lumen and neointima is generated by SMC and extracellul ar matrix. Increasing amounts of endothelial cells are found on the luminal surface of the stent neointima. Complete reendotheliazation is first noted in the chronic phase three months after stenting. Matrix structures an inc reasing whereas the amount of SMC decreases. In all phases of stent incorpo ration, the alloplastic stent material is covered by a thin (few nanometer) proteinaceous layer.