Coronary stent
Encyclopedia
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 and have been shown to improve survivability in the event of an acute myocardial infarction
.
Similar stents and procedures are used in non-coronary vessels e.g. in the legs in peripheral artery disease.
s. More recent are drug-eluting stent
s.
In development are stents with biocompatible surface coatings which do not elute drugs, and also absorbable stents (metal or polymer).
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.
s are involved in the clotting process, patients must take dual antiplatelet
therapy afterwards, usually clopidogrel
and aspirin
for one year and aspirin
indefinitely. In order to reduce the treatment, new generation of stent has been developed with biodegradable polymer.
However, the dual antiplatelet therapy may be insufficient to fully prevent clots that may result in stent thrombosis
; these and the cell proliferation may cause the standard (“bare-metal”) stents to become blocked (restenosis
). Drug-eluting stent
s were designed to lessen this problem; by releasing an antiproliferative drug (drugs typically used against cancer or as immunosuppressant
s), they can help avoid this in-stent restenosis (re-narrowing).
A more permanent and successful way to prevent heart attacks in patients at high risk is to give up smoking, exercise, and take "drugs to get blood pressure under control, drive cholesterol levels down and prevent blood clotting".
Some cardiologists believe that stents are over-used; however, in certain patient groups, such as the elderly, GRACE and other studies have found evidence of underuse. Guidelines recommend a stress test before implanting stents, but most patients do not receive a stress test.
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.
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 stent
s, resorbable stents, and others. Restenosis can be treated with a reintervention using the same method.
Stent
In the technical vocabulary of medicine, a stent is an artificial 'tube' inserted into a natural passage/conduit in the body to prevent, or counteract, a disease-induced, localized flow constriction. The term may also refer to a tube used to temporarily hold such a natural conduit open to allow...
placed in the coronary arteries that supply the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
, to keep the arteries open in the treatment of coronary heart disease
Coronary heart disease
Coronary artery disease is the end result of the accumulation of atheromatous plaques within the walls of the coronary arteries that supply the myocardium with oxygen and nutrients. It is sometimes also called coronary heart disease...
. It is used in a procedure called percutaneous coronary intervention
Percutaneous coronary intervention
Percutaneous coronary intervention , commonly known as coronary angioplasty or simply angioplasty, is one therapeutic procedure used to treat the stenotic coronary arteries of the heart found in coronary heart disease. These stenotic segments are due to the build up of cholesterol-laden plaques...
(PCI). Stents reduce chest pain and have been shown to improve survivability in the event of an acute myocardial infarction
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
.
Similar stents and procedures are used in non-coronary vessels e.g. in the legs in peripheral artery disease.
History
The first type, developed by John Robert Dugan of Shelbyville, IN, were bare-metal stentBare-metal stent
Bare-metal stent is a vascular stent without a coating . It is a mesh-like tube of thin wire. The first stents licenced for use in cardiac arteries were bare metal - often 316L stainless steel...
s. More recent are drug-eluting stent
Drug-eluting stent
A drug-eluting stent ' is a peripheral or coronary stent placed into narrowed, diseased peripheral or coronary arteries that slowly releases a drug to block cell proliferation. This prevents fibrosis that, together with clots , could otherwise block the stented artery, a process called restenosis...
s.
In development are stents with biocompatible surface coatings which do not elute drugs, and also absorbable stents (metal or polymer).
Placement
Interventional cardiology
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 angioplasty by interventional radiologist, Dr. Charles...
uses angiography to assess the location and estimate the size of the blockage ("lesion") by injecting a contrast medium
Contrast medium
A medical contrast medium is a substance used to enhance the contrast of structures or fluids within the body in medical imaging...
through the guide catheter and viewing the flow of blood through the downstream coronary arteries. Intravascular ultrasound
Intravascular ultrasound
Intravascular ultrasound 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 catheter is attached to computerized ultrasound equipment...
(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
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...
. 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 plateletPlatelet
Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days...
s are involved in the clotting process, patients must take dual antiplatelet
Antiplatelet drug
An antiplatelet drug is a member of a class of pharmaceuticals that decrease platelet aggregation and inhibit thrombus formation...
therapy afterwards, usually clopidogrel
Clopidogrel
Clopidogrel is an oral, thienopyridine class antiplatelet agent used to inhibit blood clots in coronary artery disease, peripheral vascular disease, and cerebrovascular disease. It is marketed by Bristol-Myers Squibb and Sanofi-Aventis under the trade name Plavix. The drug works by irreversibly...
and aspirin
Aspirin
Aspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer...
for one year and aspirin
Aspirin
Aspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer...
indefinitely. In order to reduce the treatment, new generation of stent has been developed with biodegradable polymer.
However, the dual antiplatelet therapy may be insufficient to fully prevent clots that may result in stent thrombosis
Thrombosis
Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot to prevent blood loss...
; these and the cell proliferation may cause the standard (“bare-metal”) stents to become blocked (restenosis
Restenosis
Restenosis literally means the reoccurrence 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 subsequently become renarrowed...
). Drug-eluting stent
Drug-eluting stent
A drug-eluting stent ' is a peripheral or coronary stent placed into narrowed, diseased peripheral or coronary arteries that slowly releases a drug to block cell proliferation. This prevents fibrosis that, together with clots , could otherwise block the stented artery, a process called restenosis...
s were designed to lessen this problem; by releasing an antiproliferative drug (drugs typically used against cancer or as immunosuppressant
Immunosuppressant
An immunosuppressant is any substance that performs immunosuppression of the immune system. They may be either exogenous, as immunosuppressive drugs, or endogenous, as ,e. g., testosterone...
s), they can help avoid this in-stent restenosis (re-narrowing).
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 below). The artery-opening stent can temporarily alleviate chest pain, but do not contribute to longevity. The "vast majority of heart attacks do not originate with obstructions that narrow arteries."A more permanent and successful way to prevent heart attacks in patients at high risk is to give up smoking, exercise, and take "drugs to get blood pressure under control, drive cholesterol levels down and prevent blood clotting".
Some cardiologists believe that stents are over-used; however, in certain patient groups, such as the elderly, GRACE and other studies have found evidence of underuse. Guidelines recommend a stress test before implanting stents, but most patients do not receive 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 muscleSmooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
tissue inside the lumen
Lumen (anatomy)
A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...
, 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
Restenosis
Restenosis literally means the reoccurrence 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 subsequently become renarrowed...
), 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 stent
Drug-eluting stent
A drug-eluting stent ' is a peripheral or coronary stent placed into narrowed, diseased peripheral or coronary arteries that slowly releases a drug to block cell proliferation. This prevents fibrosis that, together with clots , could otherwise block the stented artery, a process called restenosis...
s, resorbable stents, and others. Restenosis can be treated with a reintervention using the same method.
- On September 4, 2007, an internationalInternational----International mostly means something that involves more than one country. The term international as a word means involvement of, interaction between or encompassing more than one nation, or generally beyond national boundaries...
study showed that some heart attack patients would be better off without using drug-coated stents in emergencyEmergencyAn emergency is a situation that poses an immediate risk to health, life, property or environment. Most emergencies require urgent intervention to prevent a worsening of the situation, although in some situations, mitigation may not be possible and agencies may only be able to offer palliative...
to open their clogged arteries (patients were 5 times more likely to die after 2 years than those who received bare-metal stentBare-metal stentBare-metal stent is a vascular stent without a coating . It is a mesh-like tube of thin wire. The first stents licenced for use in cardiac arteries were bare metal - often 316L stainless steel...
s). Dr. Valentin FusterValentin FusterValentí Fuster is a Spaniard cardiologist – the only cardiologist to receive all four major research awards from the world's four major cardiovascular organizations....
, director of the Cardiovascular Institute at Mount Sinai School of MedicineMount Sinai School of MedicineMount Sinai School of Medicine is an American medical school in the borough of Manhattan in New York City, currently ranked among the top 20 medical schools in the United States. It was chartered by Mount Sinai Hospital in 1963....
in New YorkNew YorkNew York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
said stents are less commonly used in EuropeEuropeEurope is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, implanted in only about 15 % of patients there while drug-lined stents are used in up to 30% of AmericansUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
having heart attacks. The new researchResearchResearch can be defined as the scientific search for knowledge, or as any systematic investigation, to establish novel facts, solve new or existing problems, prove new ideas, or develop new theories, usually using a scientific method...
was presented by Dr. Gabriel Steg, of the Hospital Bichat-Claude Bernard in ParisParisParis is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
, at a meeting of the European Society of CardiologyEuropean Society of CardiologyThe European Society of Cardiology is a membership organisation of more than 70,000 cardiology professionals across Europe and the Mediterranean. It is involved in scientific and educational activities for cardiology professionals and also promotes cardiovascular disease prevention messages to the...
in ViennaViennaVienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...
. Dr. Eckhart Fleck, director of cardiologyCardiologyCardiology is a medical specialty dealing with disorders of the heart . The field includes diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology...
at the German Heart Institute in BerlinBerlinBerlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...
and a spokesman for the European Society of CardiologyEuropean Society of CardiologyThe European Society of Cardiology is a membership organisation of more than 70,000 cardiology professionals across Europe and the Mediterranean. It is involved in scientific and educational activities for cardiology professionals and also promotes cardiovascular disease prevention messages to the...
said that "Drug-eluting stents are not for everyone."