Coronary stents or coronary artery stents are expandable tubular medical meshwork devices used for interventional treatment of coronary artery disease and prevention of negative remodeling and vascular recoil, restenosis as well as abrupt vessel occlusion from local coronary artery dissection after coronary angioplasty.
History and etymology
The concept of coronary artery balloon angioplasty was introduced by Andreas Gruentzig in 1977 and was the mainstay of percutaneous coronary intervention in the late 1970s and 1980s. Coronary bare-metal stents were developed with implantation of the first self-expanding stent by Sigwart, Puel and colleagues in 1986 1-3. The balloon-expandable stent was developed afterwards. Consecutive optimization of implantation techniques and the introduction of dual antiplatelet therapy were made in the 1990s. A high rate of in-stent restenosis of bare metal stents led to the development of drug-eluting stents (DES) in the early 2000s, which were initially associated with similar risks of major adverse cardiovascular events (MACE) with a smaller risk of repeat revascularization in the first six months after stent placement but a higher risk thereafter 3. This lead to recommendations of extending concomitant dual antiplatelet therapy to at least 12 months 4 and the development of newer generations of drug-eluting stents in which the caliper of struts was significantly reduced and more biocompatible and durable coatings have been introduced including ‘polymer free’ coatings 2.
Indications for percutaneous coronary intervention or coronary angioplasty with stent placement include the following conditions 2,5:
acute coronary syndrome
- acute ST-elevation myocardial infarction
- non-ST elevation myocardial infarction
- unstable angina
- chronic coronary syndromes or stable coronary artery disease
- coronary artery disease with stable angina and high-grade coronary artery stenosis
- coronary artery disease with stable angina and signs of ischemia on noninvasive stress testing
Contraindications for percutaneous coronary intervention or coronary stenting include the following:
- extensive vessel occlusion with little perspective for success
- transmural infarction with significant wall-thinning
- inability to take antiplatelet medications
- significant anemia
- significant thrombocytopenia
- sepsis with bacteremia and renal failure (relative)
The following types of coronary artery stents have been used 2-4:
- bare-metal stents (BMS)
- drug-eluting stents (DES)
- metallic stent skeleton (stainless steel, cobalt-chromium or platinum-chromium)
- antiproliferative drug (1st gen.: sirolimus or paclitaxel, 2nd gen.: zotarolimus or everolimus)
- agent carrier (coating with polymer and newer biodegradable and ‘polymer free’ technologies)
- bioresorbable scaffold (BRS): bioresorbable skeleton
- drug-eluting balloons
The procedure in which coronary artery stents are employed is called percutaneous coronary intervention (PCI). It is done during an invasive coronary angiography (ICA) after initial balloon angioplasty.
- initial preparation with balloon angioplasty
- stent advancement over coronary wire under fluoroscopic guidance
- proper positioning at the location of the respective coronary lesion or plaque
- stent fixation(e.g. by means of insufflation of the stent delivery balloon)
- control imaging to confirm stent expansion and to rule out coronary edge dissection
Complications and problems of coronary artery stents include the following 2-6:
- acute stent thrombosis
- subacute stent thrombosis (up to 30 days after stent placement)
- in-stent restenosis due to neointimal hyperplasia
- hypersensitivity towards the metal framework or polymer coating
- incomplete endothelialization with delayed/impaired arterial healing and chronic inflammation
- coronary artery dissection
- stent displacement
- stent fracture
- coronary artery aneurysms
Depending on size, coronary artery stents might be seen and identified on a normal chest x-ray.
On invasive coronary angiography (ICA) bare-metal stents and drug-eluting stents will be visible as a tubular metal framework and should be snug to the coronary artery wall once set free.
CT can be used for the visualization of the coronary stent. Bare metal and common drug-eluting stents coronary stents contain a metal framework with a metallic appearance in line with the respective coronary artery and with variable amounts of beam-hardening artifacts. Assessment of in-stent stenosis highly depends on the employed stent and will not be possible in several implants. Step-and-shoot acquisition and a dedicated kernel are associated with less blurring and offer a better differentiation of the in-stent lumen and struts compared with a helical retrospective acquisition and a soft kernel 7-9.
Due to the metallic backbone of bare metal stents and usual drug-eluting stents, they will be hypointense on all sequences and are usually only visualized on 3D-imaging or coronary MR angiography.
The radiological report should include a description of the following features based on the AHA coronary artery segment model 9:
- location of the stent
- in-stent stenosis, stent patency or statement whether the stent is not evaluable
- coronary artery disease
- signs of positive or negative remodeling
Coronary stents significantly reduce complications and limitations of pure balloon angioplasty as acute vascular recoil, restenosis and acute coronary occlusion due to dissection in the early postintervention period 1.
High rates of acute stent thrombosis due to neointimal hyperplasia have been reduced with the use of drug-eluting stents (DES) and delayed arterial healing associated with those could be improved by the reduction of strut size, newer antiproliferative agents, coating or carrier-free technologies 1.
A disadvantage of drug-eluting stents versus bare-metal stents is a slightly higher risk of subacute and late stent thrombosis due to incomplete endothelialization than in bare-metal stents which can be mitigated by dual antiplatelet therapy 2-4.
Bioresorbable scaffolds still suffer from lesser mechanical stability versus newer-generation drug-eluting stents 1 and drug-eluting balloons are predominantly used in very small caliper vessels.
- drug-eluting stents (DES): reduced risk of early in-stent restenosis due to neointimal hyperplasia
- bare-metal stents (BMS): reduced risk of delayed arterial endothelialization
- bioresorbable scaffold (BRS): completely biodegradable
- drug-eluting balloons: option used for drug application in thin caliper vessels
- drug-eluting stents (DES): increased risk of delayed/impaired arterial endothelialization and healing
- bare-metal stents (BMS): neointimal hyperplasia
- bioresorbable scaffold (BRS): decreased mechanical stability and greater strut size associated with the risk of arterial injury
- drug-eluting balloons: no scaffold, vascular recoil, dissection etc.
According to a statement on the website MRIsafety.com, all patients with commercially available coronary artery stents can be scanned at 1.5 tesla and 3 tesla magnets even immediately after stent placement as long as specific parameters are followed including 10:
- only 1.5 tesla (64 MHz) or 3 tesla (128 MHz)
- whole body averaged specific absorption rate (SAR) ≤2 W/kg
- maximum imaging time ≤15 min per pulse sequence
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- 10. Shellock FG. Guidelines for the Management of Patients with Coronary Artery Stents Referred for MRI Procedures. wwwMRIsafety.com [accessed 022021]Coronary Stent - MRIsafety