By Francesco Prati
Drug-eluting stents (DES) have been found to dramatically reduce the incidence of restenosis. However, this remarkable clinical result was obtained at the price of an increased late and very late stent thrombosis, leading to catastrophic clinical events, such as acute myocardial infarction or sudden cardiac death.
Stent thrombosis is mainly due to incomplete tissue coverage of metallic stent struts. The contact between metallic struts and blood elements may lead to platelet adhesion and trigger vessel thrombosis.The vast majority of stent thrombosis occurs in the acute and subacute phase, and is more common in patients with acute coronary syndromes (ACS), due to the thrombotic milieu in which stent struts are positioned.
Preliminary studies showed that optical coherence tomography (OCT), a novel intravascular imaging modality with an excellent resolution, can detect even extremely thin rims of tissue and distinguish covered stent struts from uncovered ones that are more prone to cause late and very late stent thrombosis.
Serial OCT studies at defined time points clarified the timing of stent tissue coverage. For example, six months after deployment of a first-generation DES, the prevalence of strut coverage with neointima was 89%. This figure was found to be higher (94.3%) in the HORIZONS OCT substudy and after positioning of zotarolimus-eluting stents in the clinical setting of ST elevation acute coronary syndromes. Our Rome Heart Research group, in the last years, has provided new data on the early vessel healing after stenting. One week after the implantation of first generation paclitaxel-eluting and sirolimus-eluting stents, the stent struts coverage was found to be 86%.
Although OCT is not capable of studying tissue at a cellular level, and therefore cannot discriminate the different kinds of tissues covering stent struts (i.e., endothelium, smooth muscle cells, extracellular matrix, etc.), it is the only validated technique capable of addressing possible healing after human coronary stenting.
Our group in Rome, after the evaluation of many serial OCT studies, has suggested the concept that if the stent struts are covered early (one week in the cases evaluated in our centre), they are covered even at a later stage (two months in the cases evaluated in our centre), reducing the risk of platelet adhesion, being even a thin rim of stent tissue coverage able to avoid the contact between metallic struts and blood elements. OCT can therefore address vessel healing after bare metal stent, DES and novel technical solution such as the Avantgarde stent. In fact recently the preliminary OCT data from the On-Guard study, obtained at 4–7 days after acute myocardial infarction, provided new insights into the benefits represented by the permanent i-Carbofilm coating on the Avantgarde stent surface.
OCT data have shown an excellent 95% strut coverage after few days in the unfavorable thrombotic mileu of acute myocardial infarction. As a new concept the integral and permanent i-Carbofilm coating improves haemo- and bio-compatibility of the stent and reduces the risk of stent thrombosis, whilst the extremely thin strut thickness reduces the amount of late neointima and consequently the risk of late restenosis. Further data are needed to confirm the excellent animal and human preliminary OCT data.
Francesco Prati, San Giovannni Hospital, Rome, Rome Heart Research. Francesco Prati has no interests to declare.