Coronary stent

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An example of a coronary stent. This stent is labeled as a drug-eluting stent.

A coronary stent is a stent placed in a coronary artery to treat coronary heart disease as part of a procedure called percutaneous coronary intervention (PCI).

1 History
2 Placement
3 Re-occlusion
4 Controversy
5 See also
6 References
7 External links

[edit] History

Main article: History of invasive and interventional cardiology

The first type were bare metal stents. More recent are drug-eluting stents.

In development are bioabsorbable/biodegradable coronary stents.

[edit] Placement

Diagram of stent placement. In A, the catheter is inserted across the lesion. In B, the balloon is inflated, expanding the stent and compressing the plaque. In C, the catheter and deflated balloon have been removed. Before-and-after cross sections of the artery show the results of the stent placement.

Treating a blocked ("stenosed") coronary artery with a stent follows the same steps as other angioplasty procedures with a few important differences. The interventional cardiologist uses angiography to assess the location and estimate the size of the blockage ("lesion") by injecting a contrast medium through the guide catheter and viewing the flow of blood through the downstream coronary arteries. Intravascular ultrasound (IVUS) may be used to assess the lesion's thickness and hardness ("calcification"). The cardiologist uses this information to decide whether to treat the lesion with a stent, and if so, what kind and size. Drug eluting stents are most often sold as a unit, with the stent in its collapsed form attached onto the outside of a balloon catheter. Outside the US, physicians may perform "direct stenting" where the stent is threaded through the lesion and expanded. Common practice in the US is to predilate the blockage before delivering the stent. Predilation is accomplished by threading the lesion with an ordinary balloon catheter and expanding it to the vessel's original diameter. The physician withdraws this catheter and threads the stent on its balloon catheter through the lesion. The physician expands the balloon which deforms the metal stent to its expanded size. The cardiologist may "customize" the fit of the stent to match the blood vessel's shape, using IVUS to guide the work.^[1] It is critically important that the framework of the stent be in direct contact with the walls of the vessel to minimize potential complications such as blood clot formation. Very long lesions may require more than one stent -- this result of this treatment is sometimes referred to as a "full metal jacket".^[2]

The procedure itself is performed in a catheterization clinic ("cath lab"). Barring complications, patients undergoing catheterizations are kept at least overnight for observation.^[3]

[edit] Re-occlusion

Coronary artery stents, typically a metal framework, can be placed inside the artery to help keep it open. However, as the stent is a foreign object (not native to the body), it incites an immune response. This may cause scar tissue (cell proliferation) to rapidly grow over the stent. In addition, there is a strong tendency for clots to form at the site where the stent damages the arterial wall. Since platelets are involved in the clotting process, patients must take antiplatelet therapy afterwards, usually clopidogrel for six months and aspirin indefinitely.^[4]

However, the antiplatelet therapy may be insufficient to fully prevent clots; these and the cell proliferation may cause the standard (“bare-metal”) stents to become blocked. Drug-eluting stents were designed to lessen this problem; by releasing an antiproliferative drug (drugs typically used against cancer or as immunosuppressants), they can help avoid this in-stent restenosis (re-narrowing).

[edit] Controversy

Therapy: Stent implantation versus Coronary bypass surgery. Coronary heart disease (CHD) is a major cause of morbidity and mortality throughout the world, and both surgical revascularisation (coronary artery bypass grafting, CABG) and percutaneous coronary intervention (PCI) are established treatment options. The rapid developments in both surgical and percutaneous techniques have been such that the choice of the optimum revascularisation strategy is changing, often without an established evidence base; this is particularly true in complex conditions including patients with three-vessel and left main stem anatomy. The widespread use of drug eluting stents has resulted in a significant reduction in patients referred for CABG although published data favours the surgical approach in this high-risk group.

The SYNTAX Trial^[5] aims to explore the interface between treatment with CABG and PCI in patients with three-vessel and left main stem disease, comparing CABG using contemporary techniques and PCI using drug eluting TAXUS stents. The aim of the trial is to establish non-inferiority of PCI with CABG. The unique feature of the SYNTAX trial is the ‘all comers’ strategy. A team comprising a cardiac surgeon and an interventional cardiologist assesses each patient; if equivalent revascularisation is applicable using both techniques, the patient is accepted for randomization; if either CABG or PCI is deemed unsuitable for technical reasons or the presence of co-morbidities, then the patient is recruited into one of two parallel registries which will track these patients undergoing either CABG or PCI. The patient will not be included in the randomized cohort. 1800 patients will be randomized (1:1) between CABG and PCI. The primary end-point is a major adverse, cardiac and cerbrovascular event at one year. All patients will be followed for five years. Of the 1800 patients, 710 with left main stem disease will be randomized between CABG and PCI. In this sub-group, repeat cardiac catheterisation will be undertaken after the one-year primary endpoint to determine graft and native vessel patency (the Le Mans sub-study).

The SYNTAX Trial is one of the most important trials ever undertaken in the field of coronary revascularisation and will provide a rational basis for choosing the optimum revascularisation strategy in patients for many years to come.

- Problems: One of the drawbacks of vascular stents is the potential development of a thick smooth muscle tissue inside the lumen, the so-called neointima. Development of a neointima is variable but can at times be so severe as to re-occlude the vessel lumen (restenosis), especially in the case of smaller diameter vessels, which often results in reintervention. Consequently, current research focuses on the reduction of neointima after stent placement. Considerable improvements have been made, including the use of more bio-compatible materials, anti-inflammatory drug-eluting stents, resorbable stents, and others. Fortunately, even if stents are eventually covered by neointima, the minimally invasive nature of their deployment makes reintervention possible and usually straightforward.

On September 4, 2007, an international study showed that some heart attack patients would be better off without using drug-coated stents in emergency to open their clogged arteries (patients were 5 times more likely to die after 2 years than those who received metal stents). Dr. Valentin Fuster, director of the Cardiovascular Institute at Mount Sinai School of Medicine in New York said stents are less commonly used in Europe, implanted in only about 15 % of patients there while drug-lined stents are used in up to 30% of Americans having heart attacks. The new research was presented by Dr. Gabriel Steg, of the Hospital Bichat-Claude Bernard in Paris, at a meeting of the European Society of Cardiology in Vienna. Dr. Eckhart Fleck, director of cardiology at the German Heart Institute in Berlin and a spokesman for the European Society of Cardiology said that "Drug-eluting stents are not for everyone."^[6]