Читать книгу Interventional Cardiology - Группа авторов - Страница 246

OCT offers data concerning the underlying pathophysiology that contributes to in‐stent restenosis (ISR), such as stent underexpansion, strut fracture, strut distribution, neointimal hyperplasia and neoatherosclerosis [101]. Unlike with IVUS that may miss poorly echogenic neointima OCT can perfectly delineate the lumen shape and characteristics of neointimal tissue. Yet, because of reduced tissue penetration of OCT, plaque behind the stent struts is poorly visualized [102]. OCT accurately measures the percentage of neointimal volume obstruction and has become a standard in trials assessing the efficacy and safety of novel stents [103]. Various ISR tissue patterns have been defined based on optical homogeneity (homogenous, heterogeneous, and layered), restenotic tissue backscatter (high, low), visibility of microvessels, lumen shape (regular, irregular), and the presence of intraluminal components [104]. Bare metal stents are associated with more homogenous patterns with low echogenicity components around struts representing a counterpart of the giant cell reaction [105,106]. The typical pseudoaneurysms described by Raeber et al around first generation paclitaxel and sirolimus eluting stents with IVUS are rare with modern thin‐strut DES. On the contrary, second generation DES are not spared by a pathological phenomenon such as neoatherosclerosis, well studied by OCT. Emerging data claim the relevance of late de novo neoatherosclerosis in mimicking ISR or thrombosis [107,108].

In ISR, OCT can also be used to precisely follow the irregular lumen contour after cutting balloon and to guide cutting balloon sizing. In particular, OCT can confirm if cutting balloons have scored the plaque up to the stent at multiple points, which greatly facilitates extrusion and lumen expansion. This is possible because metal struts are powerful enough light reflectors to be visualized through very thick plaques. Through an OCT‐guided cutting balloon strategy, intimal hyperplasia was reduced from 69% to 25% in the stented segment with the minimal lumen area allowing better preparation for drug‐eluting balloon dilatation [68].

Optimal stent expansion can frequently be compromised when there is a calcium burden that has not been adequately treated or fractured prior to stent deployment. OCT is able to accurately assess the MSA which is not achievable with angiography alone. Treatment of these lesions remains challenging and may require frequent non‐compliant balloon inflations with escalating size, excimer laser coronary atherectomy (ELCA) or IVL. Unfortunately, it is found that despite best efforts with these therapies the result on final OCT shows a less than ideal MSA. It is further confirmation that intravascular imaging pre‐treatment for de novo lesions remains instrumental in avoiding such scenarios.

Neo‐intimal hyperplasia and neoatherosclerosis can be comprised of mixed morphology with fibrotic, calcific or lipid components. OCT is significant in guiding the direct therapy of these lesions. If it is determined that there is only one layer of stent and it is fibrotic or lipidic, it is recommended to pre‐treat with a balloon and implant another stent. If two or more layers are visualized or if plaque morphology is calcific in nature, treatment options may include ELCA, rotational atherectomy, non‐compliant balloon or vascular brachytherapy.

Imaging with OCT confirms the underlying mechanisms for ISR and allows for precise tailoring of appropriate therapy for each type of ISR.