Читать книгу Interventional Cardiology - Группа авторов - Страница 245

The possibility to detect thin layers of tissue coverage and neointima formation in DES over time is an interesting application of OCT to investigate the underlying mechanisms implicated in stent failure, such as stent thrombosis, in‐stent restenosis, and neoatherosclerosis. Delayed neointimal healing has been considered a possible underlying substrate of fatal stent thrombosis [78,97]. The percentage of uncovered stent struts represents the best morphometric predictor of late DES thrombosis and the risk increases with the percentage of uncovered stent struts per section [78].

An important caveat is the inability of OCT to detect reendothelialization when the layer is below its axial resolution and to differentiate between neointima and other pathologic components such as fibrin or thrombus. The latter becomes an issue at very early phases after stenting, when the prevalence of struts covered by fibrin is high. Thus, DES may appear completely covered already 1–3 days after implantation, but with fibrin instead of a mature neointima, with smooth muscle cells and matrix covered by endothelium. The low discriminative power of OCT results in false coverage rates of 45–76%in the first weeks after DES implantation [98]. The analysis of optical density might aid discriminating between neointima and fibrin [99, 100]. The greatest interest, however, is to assess intimal coverage at late follow‐up, when the prevalence of fibrin‐covered struts is low and the practical impact of this limitation is minimal. Significant differences exist in stent strut coverage and apposition between various DES at 3–12 months post implantation and this could explain the different clinical results obtained with second generation compared with first generation DES [100]. Strut thickness and biocompatibility of the polymer that could trigger inflammatory reactions have been compared, offering a possible surrogate for MACE, so low with modern stents to make studies with clinical endpoints in need of a too large population to be feasible.