Coronary heart disease is the main causes of death in most of the countries. A shift is observed in the presentation of disease with a reducing number of ST-segment elevation myocardial infarctions (STEMIs), with healthcare improvements largely due to earlier reperfusion strategies such as percutaneous coronary intervention (PCI).
The ideal strategy for handling coronary artery disease (CAD) in patients with lipid dysmetabolic disease and restenosis was established as the targeted delivery of drugs with early bare-metal stents (BMSs) gradually replaced by drug-eluting stents (DESs). Localized drug delivery affecting through a paracrine mechanism is the advantage. But some patients may have more complex vascular lesions, and the use of targeted delivery of drugs may be ineffective with potentially harmful side effects. The development of neo-atherosclerosis may represent another rare factor contributing to the onset of late thrombotic events. Unstable features of neo-atherosclerosis, even though identified in both BMSs and DESs, appear to be related to shorter durability only for DESs.
Evolution of stents
The conceptual and technologic evolution of these devices from bare-metal stents led to the creation and wide application of drug-eluting stents.
First Generation of Drug-Eluting Stents:
The Cypher and Taxus are the first two original drug-eluting stents that were approved by the Food and Drug Administration (FDA) after scientific evidence reported efficacy in reducing restenosis compared to bare-metal stents. It is the combination of a stainless steel scaffold and a permanent polymer coating and with releasing either sirolimus (Cypher stent) or paclitaxel (Taxus stent). The advantage is they had shown efficacy in preventing smooth muscle cell (SMCs) proliferation and migration, while neointimal atherosclerotic change (neo-atherosclerosis) after BMS implantation in patients who were managed with a BMS occurred beyond 5 years. And the disadvantage that the DES was associated with decreased endothelialization and retarded recovery, resulting in increased risk of late in-stent thrombosis. It was debated for the long-term safety and efficacy of BMSs due the higher risk of restenosis after implantation.
Second Generation of Drug-Eluting Stents:
Even after the benefit of the first generation of drug-eluting stents was demonstrable, the second generation reduced the late safety issues that were seen with first-generation DESs. Greater late safety and effectiveness performance compared to bare-metal stents is observed by the use of the second generation drug-eluting stents.
The second generation of drug-eluting stents heralded an improvement over the previous Taxus and Cypher models with a greater emphasis on drug release kinetics, more efficient geometry, and advances in the biocompatibility of the materials used. The PCI platform was enriched with a new addition:
- Cobalt-chromium everolimus-eluting stents (CoCr-EESs) (Abbott Vascular, Santa Clara, CA, USA),
- Platinum-chromium EESs (PtCr-EESs) (Boston Scientific, Massachusetts, US),
- Phosphorylcholine-based zotarolimus-eluting stent (PC-ZES), Resolute ZES (Re-ZES) (Medtronic),
- Biolimus-eluting stent (BES) (BioMatrix, Biosensors, Newport Beach, CA, USA; and Nobori, Terumo Clinical Supply, Kakamigahara, Japan).
New Frontiers of stenting
Research has shifted to other design approaches for the development of new stents due to thrombosis, and restenosis of stents, even after there is a strong increase in the PCI and stenting procedure using the second generation of DES.
A new direction for the prevention of thrombosis is the use of heparin incorporated in the device, which negates the prothrombotic components on the stent. The use of heparin impregnated on the surface of the stent can be a valid option to prevent restenosis of the device due to the reactive formation of thrombi on the metallic core. This device known as Viabahn is made by assembling a nitinol core which is coated with ePTFE and non-mobilizable heparin. The Viabahn stent has been proven to have better patency rates in clinical trials than the bare-metal stent.
Bioresorbable Vascular Scaffolds
To overcome DES limitations such as in-stent restenosis, use of a bioresorbable vascular stent (BDES or BVS) in clinical practice has been suggested. Bioresorbable DESs or vascular scaffolds (BVSs) were initially designed from metallic or polymeric compounds.
Future direction for the stent design
Gene-eluting stents can adapt the local microenvironment to reduce hyperplasia and intimal thrombosis. Future directions will be focused on developing newer stent materials and therapies available with tailored dosing kinetics. This evolution in personalization can determine the selection of the stent, which can be adapted to the needs of a single patient, offering the most advantageous dosage compared to one or more specific therapies for long-term patients for a precise duration.
When an implanted device includes an active ingredient, and released into vessel walls and into the blood is strongly influenced by the hemodynamics around the device and the kinetics of release. The whole scenario is then challenging and fascinating, as it involves mechanics, fluid dynamics, and mass transfer processes, but a holistic approach is required to find the right solution to improve outcomes of stent and cardiac grafts.
The widespread use of different polymers in coronary stenting and the multiple clinical implications that can be hypothesized, starting from basic science studies, should be carefully investigated in the cardiologic scenario. It appears crucial to summarize all the recent evidence on this topic with the aim of portraying the literary landscape for future tailored studies.