What Is the Optimal Stent Design? – The Pathologist’s Opinion

More than 5 millions stents have been implanted in patients all over the world and it is estimated that the number will increase to 6.6 million by 2020. It has been almost 30 years since the first stent was implanted in man. Initially, stents were mainly used for bail out in patients with acute occlusion due to coronary dissection following balloon angioplasty. The first stents were typically mounted on high profile, rigid delivery platforms and were difficult to deploy, leading to acute/subacute stent thrombosis. Greater understanding of the need for effective antiplatelet therapy and also improvement in delivery and better stent designs helped to overcome early stent thrombosis. The resulting lower rates of restenosis as compared to balloon angioplasty propelled the use of stents in routine practice. However, restenosis was the “Achilles heel” of bare metal stents and the birth of drug eluting stents (DES) helped dramatically reduce restenosis but late stent thrombosis became an issue. Second generation DES have reduced the incidence of late stent thrombosis however, one of the mechanisms of late stent thrombosis is the development of atherosclerosis within the stented segment (“neoatherosclerosis”), which remains an issue because its development is increased in DES compared to BMS. Recently, third generation DES, using bioabsorable polymer rather than permanent polymer to deliver drug and fully biodegradable vascular scaffolds are available. Many believe that these will overcome the drawback of stenting as no permanent metal or polymer will be left behind. Studies in animals show that when bioabsorable polymers are used the endothelial lining is far more competent as compared to permanent polymers that have been shown to induce hypersensitivity reaction. Also, clinical studies have shown that bioabsorable polymers induce less late thrombosis as compared to permanent polymers. Similarly, in fully bioabsorbable scaffolds, the vascular reactivity and lumen enlargement are seen between 1 and 2 years after implantation and the polymers get replaced by proteoglycan matrix and collagen over time and that mild to moderate inflammation is associated with vessel enlargement. Overall what remains unclear is that bulky scaffolds ≥150 μm thickness may be associated again with greater late stent thrombosis. Therefore, we have to remain vigilant that we do not implant these fully bioabsorbable polymeric scaffolds in patients presenting with acute myocardial infarction until clearly clinical trials prove their safety.