Casting light on coronary evaginations: different mechanisms in different coronary devices?

Stent thrombosis (ST) remains a major concern due to high morbidity and mortality in both the short and long term. Although the rates of this complication have been reduced with newer generation drug-eluting stents (DES), the risk of ST continues to persist for all DES and was recently also reported in bioresorbable vascular scaffolds (BVS). – 4 Among the suggested causes of ST are incomplete neointimal formation, malapposition, hypersensitivity reactions, positive remodelling, and neoatherosclerosis. Intracoronary optical coherence tomography (OCT)—a near-infrared light-based technology with an ultrahigh resolution (10 mm)—visualizes in detail the majority of these features which are also seen in asymptomatic patients. OCT has therefore become the tool of choice to study their clinical importance and natural history in order to prevent future ST. In this endeavour, a new phenomenon, coronary evagination, has been observed by OCT in DES, and proposed to be an additional risk factor of late and very late ST. In the present issue of the journal, Gori and colleagues describe, using OCT at 12 months follow-up, the incidence, predictors, and possible mechanisms of evaginations following implantation of the everolimus-eluting Absorb BVS (Abbott Vascular, USA). Out of the 102 studied lesions, 54% exhibited one or more evaginations, whereas the entity ‘major evagination’ was rare. Evaginations were strongly associated with malapposition and strut fractures, as well as with peri-strut low-intensity areas (PSLIAs), thought to represent poor scaffold healing. The proposed mechanism of evaginations in this BVS cohort was scaffold undersizing. The study is exciting as it for the first time reports coronary evaginations in the Absorb BVS, and proposes a different mechanism from that in DES. Nevertheless, interpretation of the results requires careful consideration of the methods, and a general acquaintance with the unusual terminology of features studied in relation to coronary evaginations.