A coronary stent is a
tube-shaped device placed in the
coronary arteries
The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ of ...
that supply
blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...
to the
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...
, to keep the arteries open in the treatment of
coronary heart disease
Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pla ...
. It is used in a procedure called
percutaneous coronary intervention
Percutaneous coronary intervention (PCI) is a non-surgical procedure used to treat narrowing of the coronary arteries of the heart found in coronary artery disease. The process involves combining coronary angioplasty with stenting, which is the ...
(PCI). Coronary stents are now used in more than 90% of PCI procedures.
Stents reduce
angina
Angina, also known as angina pectoris, is chest pain or pressure, usually caused by ischemia, insufficient blood flow to the Cardiac muscle, heart muscle (myocardium). It is most commonly a symptom of coronary artery disease.
Angina is typical ...
(chest pain) and have been shown to improve survivability and decrease adverse events in an
acute myocardial infarction
A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may tr ...
.
Similar
stent
In medicine, a stent is a metal or plastic tube inserted into the lumen of an anatomic vessel or duct to keep the passageway open, and stenting is the placement of a stent. A wide variety of stents are used for different purposes, from expandab ...
s and procedures are used in non-coronary vessels (e.g., in the legs in
peripheral artery disease
Peripheral artery disease (PAD) is an abnormal narrowing of arteries other than those that supply the heart or brain. When narrowing occurs in the heart, it is called coronary artery disease, and in the brain, it is called cerebrovascular diseas ...
).
Medical uses
Arterial Stenting 3D Medical Animation An artery with a stent follows the same steps as other
angioplasty procedures with a few important differences. The
interventional cardiologist
Interventional cardiology is a branch of cardiology that deals specifically with the catheter based treatment of structural heart diseases. Andreas Gruentzig is considered the father of interventional cardiology after the development of angioplast ...
uses
angiography
Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is performe ...
to assess the location and estimate the size of the blockage ("lesion") by injecting a
contrast medium
A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiop ...
through the guide catheter and viewing the flow of blood through the downstream coronary arteries.
Intravascular ultrasound
Intravascular ultrasound (IVUS) or intravascular echocardiography is a medical imaging methodology using a specially designed catheter with a miniaturized ultrasound probe attached to the distal end of the catheter. The proximal end of the cath ...
(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 to the outside of a balloon
catheter
In medicine, a catheter (/ˈkæθətər/) is a thin tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. Cath ...
. 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—the 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.
Risks
Though the chances of having complications from a PCI are small, some serious complications include the development of arrhythmias, adverse reactions/effects of the dye used in the procedure, infection, restenosis, clotting, blood vessel damage, and bleeding at catheter insertion site.
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 and cause a neointimal hyperplasia. In addition, if the stent damages the artery wall there is a strong tendency for clots to form at the site. Since
platelet
Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby ini ...
s are involved in the clotting process, patients must take
dual antiplatelet therapy
An antiplatelet drug (antiaggregant), also known as a platelet agglutination inhibitor or platelet aggregation inhibitor, is a member of a class of pharmacology, pharmaceuticals that decrease platelet aggregation and inhibit thrombus formation. The ...
starting immediately before or after stenting: usually an ADP receptor antagonist (e.g.
clopidogrel
Clopidogrel — sold under the brand name Plavix, among others — is an antiplatelet medication used to reduce the risk of heart disease and stroke in those at high risk. It is also used together with aspirin in heart attacks and following ...
or
ticagrelor
Ticagrelor, sold under the brand name Brilinta among others, is a medication used for the prevention of stroke, heart attack and other events in people with acute coronary syndrome, meaning problems with blood supply in the coronary arteries. It ...
) and
aspirin
Aspirin, also known as acetylsalicylic acid (ASA), is a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and/or inflammation, and as an antithrombotic. Specific inflammatory conditions which aspirin is used to treat inc ...
for up to one year and aspirin indefinitely.
However, in some cases the dual antiplatelet therapy may be insufficient to fully prevent clots that may result in stent
thrombosis
Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (thro ...
; these clots and cell proliferation may sometimes cause standard (“bare-metal”) stents to become blocked (
restenosis
Restenosis is the recurrence of stenosis, a narrowing of a blood vessel, leading to restricted blood flow. Restenosis usually pertains to an artery or other large blood vessel that has become narrowed, received treatment to clear the blockage and s ...
).
Drug-eluting stent
A drug-eluting stent (DES) is a peripheral or coronary stent (a scaffold) placed into narrowed, diseased peripheral or coronary arteries that slowly release a drug to block cell proliferation. This prevents fibrosis that, together with clots ...
s were developed with the intent of dealing with this problem: by releasing an antiproliferative drug (drugs typically used against cancer or as
immunosuppressant
Immunosuppressive drugs, also known as immunosuppressive agents, immunosuppressants and antirejection medications, are drugs that inhibit or prevent activity of the immune system.
Classification
Immunosuppressive drugs can be classified in ...
s), they can help reduce the incidence of "in-stent restenosis" (re-narrowing).
Restenosis
One of the drawbacks of vascular stents is the potential for restenosis via the development of a thick
smooth muscle
Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...
tissue inside the
lumen, the so-called
neointima
Neointima typically refers to scar tissue that forms within tubular anatomical structures such as blood vessels, as the intima is the innermost lining of these structures. Neointima can form as a result of vascular surgery such as angioplasty
...
. Development of a neointima is variable but can at times be so severe as to re-occlude the vessel lumen (
restenosis
Restenosis is the recurrence of stenosis, a narrowing of a blood vessel, leading to restricted blood flow. Restenosis usually pertains to an artery or other large blood vessel that has become narrowed, received treatment to clear the blockage and s ...
), 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. Substantial improvements have been made, including the use of more biocompatible materials, anti-inflammatory
drug-eluting stent
A drug-eluting stent (DES) is a peripheral or coronary stent (a scaffold) placed into narrowed, diseased peripheral or coronary arteries that slowly release a drug to block cell proliferation. This prevents fibrosis that, together with clots ...
s,
resorbable stents
In medicine, a stent is any device which is inserted into a blood vessel or other internal duct to expand it to prevent or alleviate a blockage. Traditionally, such devices are fabricated from metal mesh and remain in the body permanently or unti ...
, and others. Restenosis can be treated with a reintervention using the same method.
Controversy
The value of stenting in rescuing someone having a heart attack (by immediately alleviating an obstruction) is clearly defined in multiple studies, but studies have failed to find reduction in hard endpoints for stents vs. medical therapy in stable angina patients (see controversies in
Percutaneous coronary intervention
Percutaneous coronary intervention (PCI) is a non-surgical procedure used to treat narrowing of the coronary arteries of the heart found in coronary artery disease. The process involves combining coronary angioplasty with stenting, which is the ...
). The artery-opening stent can temporarily alleviate chest pain, but does not contribute to longevity. The "...vast majority of heart attacks do not originate with obstructions that narrow arteries." Further, “...researchers say, most heart attacks do not occur because an artery is narrowed by plaque. Instead, they say, heart attacks occur when an area of plaque bursts, a clot forms over the area and blood flow is abruptly blocked. In 75 to 80 percent of cases, the plaque that erupts was not obstructing an artery and would not be stented or bypassed. The dangerous plaque is soft and fragile, produces no symptoms and would not be seen as an obstruction to blood flow.”
[
A more permanent and successful way to prevent heart attacks in patients at high risk is to give up smoking, to exercise regularly, and take "drugs to get blood pressure under control, drive cholesterol levels down and prevent blood clotting".][Kolata, Gina]
"New Heart Studies Question the Value Of Opening Arteries"
''The New York Times'', March 21, 2004. Retrieved January 14, 2011.
Some cardiologists believe that stents are overused; however, in certain patient groups, such as the elderly, GRACE and other studies have found evidence of under-use. One cardiologist was convicted of billing patients for performing medically unnecessary stenting. Guidelines recommend a stress test before implanting stents, but most patients do not receive a stress test.
Research
While revascularisation
In medical and surgical therapy, revascularization is the restoration of perfusion to a body part or organ that has had ischemia. It is typically accomplished by surgical means. Vascular bypass and angioplasty are the two primary means of rev ...
(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
A therapy or medical treatment (often abbreviated tx, Tx, or Tx) is the attempted remediation of a health problem, usually following a medical diagnosis.
As a rule, each therapy has indications and contraindications. There are many different ...
. 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-eluting stent (the Boston Scientific TAXUS paclitaxel-eluting stent). SYNTAX found the two strategies 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.
* Ischemia, a large trial of 5,179 participants followed for a median of three and a half years that was funded by the US federal government, was skeptical of the benefits of coronary stents. It divided participants into ones which received drug therapy alone, and those that also received bypass surgery or stents. The drug therapy alone group did not fare any differently than the group that received the stents as well as drug therapy. Ischemia did find that stents seemed to help some patients with angina
Angina, also known as angina pectoris, is chest pain or pressure, usually caused by ischemia, insufficient blood flow to the Cardiac muscle, heart muscle (myocardium). It is most commonly a symptom of coronary artery disease.
Angina is typical ...
, however.
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.
History
The first stent was patented in 1972 by Robert A. Ersek, MD based on work he had done in animals in 1969 at the University of Minnesota. In addition to intervascular stents, he also developed the first stent-supported porcine valve that can be implanted transcutaneously in 7 minutes, eliminating open-heart surgery.
In development are stents with biocompatible surface coatings which do not elute drugs, and also absorbable stents (metal or polymer).
References
External links
{{DEFAULTSORT:Coronary Stent
Interventional cardiology
Medical devices