Optical coherence tomography to evaluate coronary stent implantation and complications Umair Hayat a , Vikas Thondapu a , Muhammad Asrar Ul Haq a , Nicolas Foin c , Ik-Kyung Jang d and Peter Barlis a,b Coronary optical coherence tomography (OCT) is now an established imaging technique in many catheterization laboratories worldwide. With its near-histological view of the vessel wall and lumen interface, it offers unprecedented imaging quality to improve our understanding of the pathophysiology of atherosclerosis, plaque vulnerability, and vascular biology. Not only is OCT used to accurately detect atherosclerotic plaque and optimize stent position, but it can further characterize plaque composition, quantify stent apposition, and assess stent tissue coverage. Given that its resolution of 15 μm is well above that of angiography and intravascular ultrasound, OCT has become the invasive imaging method of choice to examine the interaction between stents and the vessel wall. This review focuses on the application of OCT to examine coronary stents, the mechanisms of stent complications, and future directions of OCT-guided intervention. Coron Artery Dis 26: e55–e68 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. Coronary Artery Disease 2015, 26:e55–e68 Keywords: acute coronary syndrome, coronary artery disease, coronary stents, interventional cardiology, myocardial infarction, optical coherence tomography a Cardiovascular Research Group, Melbourne Medical School, The University of Melbourne, b Department of Mechanical Engineering, Melbourne School of Engineering, University of Melbourne, Melbourne, Victoria, Australia, c National Heart Research Institute, National Heart Centre Singapore, Singapore and d Massachusetts General Hospital, Harvard University, Boston, Massachusetts, USA Correspondence to Peter Barlis, MBBS, MPH, PhD, FRACP, FESC, FACC, Melbourne Medical School, Faculty of Medicine, Dentistry & Health Sciences, The University of Melbourne, 185 Cooper Street, Epping, VIC 3076, Australia Tel: + 61 3 8405 8000; fax: + 61 3 8405 8405; e-mail: pbarlis@unimelb.edu.au Introduction Coronary stent placement is a well-established and effective treatment for occlusive coronary artery disease. Nevertheless, a small but significant number of patients develop adverse outcomes related to stent-induced vessel injury [1]. Mechanisms of in-stent restenosis (ISR) and stent thrombosis likely include uncovered stent struts, stent malapposition, neointimal hyperplasia, and neoatherosclerosis. Intracoronary optical coherence tomography (OCT) readily identifies these features and has provided significant insights into the pathogenesis of stent complications. OCT has been used successfully and safely to better characterize lumen geometry, plaque composition, culprit lesions, and acute thrombus in patients with acute cor- onary syndromes (ACSs) [2,3] (Fig. 1). OCT is also used to enhance optimal stent placement by detecting features such as edge dissection, underexpansion, malapposition, and residual thrombus that are missed by angiography alone [4]. OCT has also been used in long-term follow-up to assess for late incomplete stent apposition (ISA), uncovered stent struts, neointimal hyperplasia, neoa- therosclerosis, and other high-risk features associated with ISR and late stent thrombosis [5,6]. Although OCT has become a powerful tool to complement angiography in the catheterization laboratory, further advances in OCT-guided percutaneous coronary inter- ventions (PCIs) are expected to improve early detection and treatment of stent complications, and perhaps even help avoid stent placement entirely in certain patients [7]. This review will examine the following: (i) current mechanisms of stent failure; (ii) OCT assessment of coronary vessels and stents in the context of stent failure; and (iii) applications of OCT-guided PCI in management of ACS and stent failure. Current model of stent-induced endothelial injury and stent failure Current models of native coronary atherosclerosis show that chronic endothelial injury and inflammation are the core pathologic processes of disease progression. Similarly, ongoing research suggests that stents may induce various forms of acute and chronic endothelial injury, ultimately resulting in complications such as ISR and stent throm- bosis. Because OCT provides an exceptionally clear assessment of endothelial integrity, plaque composition, and strut-level analysis of apposition and endothelial cov- erage, it has been instrumental in much of this work. Partly on the basis of OCT imaging data, several possible sources of stent-induced injury have been identified: (i) drug-eluting stents (DES)-related inhibition of normal endothelial regeneration resulting in uncovered stent struts; (ii) stent malapposition associated with uncovered Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's website (www.coronary-artery.com). Review in depth e55 0954-6928 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/MCA.0000000000000215 Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.