Coronary stent

File:Taxus stent FDA.jpg

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

A coronary stent is a tube placed in the coronary arteries that supply the heart, to keep the arteries open in the treatment of coronary heart disease. It is used in a procedure called percutaneous coronary intervention (PCI). Stents reduce chest pain, but they have not been shown to improve survival, except in acute myocardial infarction.

Similar stents and procedures are used in non-coronary vessels e.g. in the legs in peripheral artery disease.

History

Main article: History of invasive and interventional cardiology

The first type, developed by John Robert Dugan of Shelbyville, IN, were bare-metal stents. More recent are drug-eluting stents.

In development are stents with biocompatible surface coatings which do not elute drugs, and also absorbable stents (metal or polymer).

Placement

File:PTCA stent NIH.gif

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. 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".

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

Dealing with lesions near branches in the coronary arteries presents additional challenges and requires additional techniques .

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.

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 (restenosis). 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).

Controversy

While the value of stenting in acute patients is clearly defined in multiple studies, some studies have failed to find reduction in hard endpoints for stents vs. medical therapy in stable angina patients (see below). Some cardiologists believe that stents are over-used, although in certain patient groups, for example the elderly, there is evidence from GRACE and other studies of underuse. Guidelines recommend a stress test before implanting stents, but most patients don't get a stress test.

Clinical Trials

While revascularisation (by stenting or bypass surgery) is of clear benefit in reducing mortality and morbidity in patients with acute symptoms (acute coronary syndromes) including myocardial infarction, their benefit is less marked in stable patients. Clinical trials have failed to demonstrate that coronary stents improve survival over best medical treatment.

• The COURAGE trial compared PCI with optimum medical therapy. Of note, the trial excluded a large number of patients at the outset and undertook angiography in all patients at baseline, thus the results only apply to a subset of patients and should not be over-generalised. COURAGE concluded that in patients with stable coronary artery disease PCI did not reduce the death, myocardial infarction or other major cardiac events when added to optimum medical therapy.

• The MASS-II trial compared PCI, CABG and optimum medical therapy for the treatment of multi-vessel coronary artery disease. The MASS-II trial showed no difference in cardiac death or acute MI among patients in the CABG, PCI, or MT group. However, it did show a significantly greater need for additional revascularization procedures in patients who underwent PCI.

• The SYNTAX Trial is a manufacturer-funded trial with a primary endpoint of death, cardiovascular events, and myocardial infarction, and also the need for repeat vascularization, in patients with blocked or narrowed arteries. Patients were randomized to either CABG surgery or a drug-eluding stent (the Boston Scientific TAXUS paclitaxel-eluding stent). SYNTAX found the two stratgies to be similar for hard endpoints (death and MI). Those receiving PCI required more repeat revascularisation (hence the primary endpoint analysis did not find PCI to be non-inferior), but those undergoing CABG had significantly more strokes pre or perioperatively. Use of the SYNTAX risk score is being investigated as a method of identifying those multivessel disease patients in whom PCI is a reasonable option vs those in whom CABG remains the preferred strategy.

Several other clinical trials have been performed to examine the efficacy of coronary stenting and compare with other treatment options. A consensus of the medical community does not exist.

Restenosis

One of the drawbacks of vascular stents is the potential for restenosis via the 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. Restenosis can be treated with a reintervention using the same method.

• 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 bare-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."

See also

Dr Julio Palmaz - inventor of the balloon-expandable stent

External links

pl:Stent ru:Стентирование