Coronary stents or coronary artery stents are expandable tubular medical meshwork devices used for interventional treatment of coronary artery disease and prevention of negative remodelling 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 the implantation of the first self-expanding stent by Sigwart, Puel and colleagues in 1986 ^1-3. The balloon-expandable stent was developed afterwards. Consecutive optimisation 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 revascularisation in the first six months after stent placement but a higher risk thereafter ³. This led 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 calliper of struts was significantly reduced and more biocompatible and durable coatings have been introduced including ‘polymer free’ coatings ².

Indications

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 ischaemia on noninvasive stress testing

Contraindications

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 anaemia

• significant thrombocytopenia

• sepsis with bacteraemia and renal failure (relative)

Implant design

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-generation: sirolimus or paclitaxel, 2nd-generation: zotarolimus or everolimus)

  • agent carrier (coating with polymer and newer biodegradable and ‘polymer-free’ technologies)

• bioresorbable scaffold (BRS): bioresorbable skeleton

• drug-eluting balloons

Procedure

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. employing insufflation of the stent delivery balloon)

• control imaging to confirm stent expansion and to rule out coronary edge dissection

Complications

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

Radiographic features

Plain radiograph

Depending on size, coronary artery stents might be seen and identified on a normal chest x-ray.

Coronary angiography

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

CT can be used for the visualisation 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.

MRI

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 visualised on 3D imaging or coronary MR angiography.

Radiological report

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 remodelling

Outcomes

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 calliper vessels.

Advantages

• 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 calliper vessels

Disadvantages

• 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.

Practical points

MRI

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

See also

• coronary artery disease

• myocardial ischaemia

• myocardial infarction