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An example of a drug-eluting stent. This is the TAXUS Express2 Paclitaxel-Eluting Coronary Stent System, which releases paclitaxel.
An example of a drug-eluting stent. This is the TAXUS Express2 Paclitaxel-Eluting Coronary Stent System, which releases paclitaxel. Paclitaxel is a Mitotic inhibitor used in Cancer Chemotherapy.

A drug-eluting stent is a coronary stent (a scaffold) placed into narrowed, diseased coronary arteries that slowly releases a drug to block cell proliferation. 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 Coronary circulation is the circulation of blood in the Blood vessels that supply Blood to and from the Heart muscle A drug, broadly speaking is any chemical substance that when absorbed into the body Hyperplasia (or "hypergenesis" is a general term referring to the proliferation of cells within an organ or tissue beyond that which is ordinarily seen in e This prevents fibrosis that, together with clots (thrombus), could otherwise block the stented artery, a process called restenosis. Fibrosis is the formation or development of excess fibrous Connective tissue in an organ or tissue as a reparative or reactive process as opposed to a formation of Fibrous A thrombus, or blood clot, is the final product of the Blood coagulation step in Hemostasis. Restenosis literally means the re occurrence of Stenosis. This is usually restenosis of an Artery, or other Blood vessel, but possibly The stent is usually placed within the coronary artery by an Interventional cardiologist. Interventional cardiology is a branch of the medical specialty of Cardiology that deals specifically with the catheter based treatment of structural Heart diseases

Drug-eluting stents (DES) in current clinical use were approved by the FDA after clinical trials showed they were statistically superior to bare-metal stents (BMS) for the treatment of native coronary artery narrowings, having lower rates of major adverse cardiac events (usually defined as a composite clinical endpoint of death + myocardial infarction + repeat intervention because of restenosis. Myocardial infarction ( MI or AMI for acute myocardial infarction) also known as a heart attack, occurs when the blood supply [1] [2]

Contents

History

Main article: History of invasive and interventional cardiology

The first procedure to treat blocked coronary arteries was coronary artery bypass graft surgery (CABG), wherein a section of vein or artery from elsewhere in the body is used to bypass the diseased segment of coronary artery. The history of invasive and interventional cardiology is complex with multiple groups working independently on similar technologies Coronary circulation is the circulation of blood in the Blood vessels that supply Blood to and from the Heart muscle Coronary artery bypass surgery, also coronary artery bypass graft surgery, and colloquially heart bypass or bypass surgery is a surgical procedure In 1977, Andreas Grüntzig introduced percutaneous transluminal coronary angioplasty (PTCA), also called balloon angioplasty, in which a catheter was introduced through a peripheral artery and a balloon expanded to dilate the narrowed segment of artery. Andreas Roland Grüntzig (1939– October 27, 1985) was a German radiologist who first developed successful balloon Angioplasty for Percutaneous coronary intervention ( PCI) commonly known as coronary angioplasty or simply Angioplasty, is a therapeutic procedure to treat [3]

As equipment and techniques improved, the use of PTCA rapidly increased, and by the mid-1980s, PTCA and CABG were being performed at equivalent rates. [4] Balloon angioplasty was generally effective and safe, but restenosis was frequent, occurring in ~30–40% of cases, usually within the first year after dilation. Restenosis literally means the re occurrence of Stenosis. This is usually restenosis of an Artery, or other Blood vessel, but possibly In ~3% of balloon angioplasty cases, failure of the dilation and acute or threatened closure of the coronary artery (often because of dissection) prompted emergency CABG. [4]

Dotter and Melvin Judkins had suggested using prosthetic devices inside arteries (in the leg) to maintain blood flow after dilation as early as 1964. Charles Theodore Dotter (1920-1985 was a vascular Radiologist who is generally credited with developing Interventional radiology. [5] In 1986, Puel and Sigwart implanted the first coronary stent in a human patient. [6] Several trials in the 1990s showed the superiority of stent placement over balloon angioplasty. Restenosis was reduced because the stent acted as a scaffold to hold open the dilated segment of artery; acute closure of the coronary artery (and the requirement for emergency CABG) was reduced, because the stent repaired dissections of the arterial wall. By 1999, stents were used in 84% of percutaneous coronary interventions (i. In Surgery, percutaneous pertains to any medical procedure where access to inner organs or other tissue is done via needle-puncture of the skin rather than by using an "open" e. , those done via a catheter, and not by open-chest surgery. )[6]

Early difficulties with coronary stents included a risk of early thrombosis (clotting) resulting in occlusion of the stent. Thrombosis is the formation of a blood Clot ( Thrombus) inside a Blood vessel, obstructing the flow of Blood through the Circulatory [4] Coating stainless steel stents with other substances such as platinum or gold did eliminate this problem. [6] High-pressure balloon expansion of the stent to ensure its full apposition to the arterial wall, combined with drug-therapy using aspirin and another inhibitor of platelet aggregation (usually ticlopidine or clopidogrel) nearly eliminated this risk of early stent thrombosis. Aspirin, or acetylsalicylic acid (ASA (əˌsɛtɨlsælɨˌsɪlɨk ˈæsɨd is a Salicylate drug, often used as an Analgesic to relieve Platelets, or Thrombocytes, are small cytoplasmic bodies derived from cells They circulate in the Blood of Mammals and are involved Ticlopidine (trade name Ticlid) is an Antiplatelet drug in the Thienopyridine family Clopidogrel is a potent oral antiplatelet agent often used in the treatment of Coronary artery disease, Peripheral vascular disease, and Cerebrovascular [6][4]

Though it occurred less frequently than with balloon angioplasty or other techniques, stents nonetheless remained vulnerable to restenosis, caused almost exclusively by neointimal tissue growth. Angioplasty is the technique of mechanically widening a narrowed or totally obstructed Blood vessel; typically as a result of Atherosclerosis. To address this issue, developers of drug-eluting stents used the devices themselves as a tool for delivering medication directly to the arterial wall. While initial efforts were unsuccessful, it was shown in 2001 that the release (elution) of drugs with certain specific physicochemical properties from the stent can achieve high concentrations of the drug locally, directly at the target lesion, with minimal systemic side effects [7]. As currently used in clinical practice, "drug-eluting" stents refers to metal stents which elute a drug designed to limit the growth of neointimal scar tissue, thus reducing the likelihood of stent restenosis. Restenosis literally means the re occurrence of Stenosis. This is usually restenosis of an Artery, or other Blood vessel, but possibly

The first successful trials were of sirolimus-eluting stents. Sirolimus ( INN) is a relatively new immunosuppressant drug used to prevent rejection in organ transplantation, and is especially useful in Kidney A clinical trial in 2002 led to approval of the sirolimus-eluting Cypher stent in Europe in 2002. After a larger pivotal trial (one designed for the purpose of achieving FDA approval), published in 2003, the device received FDA approval and was released in the U. S. in 2003. [6] Soon thereafter, a series of trials of paclitaxel-eluting stents led to FDA approval of the Taxus stent in 2004. Paclitaxel is a Mitotic inhibitor used in Cancer Chemotherapy. [8]

Indications

Clinical trials have shown the benefits of coronary stenting with BMS over other methods of angioplasty, including balloon angioplasty and atherectomy. Endarterectomy is a Surgical procedure to remove the atheromatous ''plaque'' material or blockage in the lining of an Artery constricted by the buildup Drug-eluting stents (DES) have also been extensively studied, and are generally superior to bare-metal stents as regards Major Adverse Cardiac Events (MACE, generally defined as death, myocardial infarction, or the need for a repeat revascularization procedure. Myocardial infarction ( MI or AMI for acute myocardial infarction) also known as a heart attack, occurs when the blood supply ) Stents are indicated to improve the diameter of the coronary artery lumen, when narrowing (generally because of atherosclerosis) causes ischemia (reduced oxygen delivery to the muscle supplied by that artery. Atherosclerosis is a Disease affecting arterial Blood vessels It is a chronic inflammatory response in the walls of arteries in large part due to the accumulation In Medicine, ischemia ( Greek ισχαιμία, isch- is restriction hema or haema is Blood) is a restriction )

Off-label use

Drug-eluting stents also have been shown to be superior to bare-metal stents in reducing short-term complications of stenting in saphenous vein grafts [9]; however, use in these bypass grafts is an example of an "off-label" use of drug-eluting stents. That is, this application has not been sufficiently examined by the Food and Drug Administration for that agency to recommend the use. For "on-label" applications, the FDA "believes that coronary drug-eluting stents remain safe and effective when used for the FDA-approved indications. These devices have significantly reduced the need for a second surgery to treat restenosis for thousands of patients each year. "[10].

As enthusiasm for the new devices abates, there is some concern about overzealous use of stents in general. Two studies found that about half of patients received stents for unapproved reasons,[11][12] with worse outcomes for the patients in both studies.

Alternatives

Medical therapy for coronary artery disease has also improved since the 1970s, and for many kinds of patients may be as successful as stenting or surgery. For those requiring PCI or surgery, medical therapy and revascularization should be viewed as complementary rather than opposing strategies. [13]

Coronary artery bypass graft surgery is the best treatment for some patients. Coronary artery bypass surgery, also coronary artery bypass graft surgery, and colloquially heart bypass or bypass surgery is a surgical procedure A recent study comparing the outcomes of all patients in New York state treated with coronary artery bypass surgery (CABG) or percutaneous coronary intervention (PCI) demonstrated CABG was superior to PCI with DES in multivessel (two or more diseased arteries) coronary artery disease (CAD). New York ( is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous Coronary artery bypass surgery, also coronary artery bypass graft surgery, and colloquially heart bypass or bypass surgery is a surgical procedure Percutaneous coronary intervention ( PCI) commonly known as coronary angioplasty or simply Angioplasty, is a therapeutic procedure to treat Coronary disease (or coronary heart disease) refers to the failure of Coronary circulation to supply adequate circulation to Cardiac muscle and surrounding Patients treated with CABG had lower rates of death and of death or myocardial infarction than treatment with a drug-eluting stent. Patients undergoing CABG also had lower rates of repeat revascularization. [14] The New York State registry included all patients undergoing revascularization for coronary artery disease, but was not a randomized trial, and so may have reflected other factors besides the method of coronary revascularization.

No randomized trial comparing CABG and DES has been completed, although two trials of DES versus CABG are currently enrolling patients - SYNTAX (Synergy Between Percutaneous Coronary Intervention With Taxus and Cardiac Surgery) and FREEDOM (Future Revascularization Evaluation in Patients With Diabetes Mellitus—Optimal Management of Multivessel Disease). The registries of the nonrandomized patients screened for these trials may provide as much robust data regarding revascularization outcomes as the randomized analysis. [15]

The ARTS II registry compared a cohort of patients treated with multi-vessel stenting with DES, to the historical CABG cohort in the ARTS I trial. At three-year follow-up, major adverse cardiac events were comparable between the ARTS II DES group and the ARTS I CABG group. Re-intervention was lower in the ARTS I CABG group. [16]

Risks

Like all invasive medical procedures, implanting stents in the coronary arteries carries risk. For the newer drug-eluting stents, very-long-term results are not yet available; however, five-years after implantation sirolimus-eluting stents remained superior to bare-metal stents. [17]

Risks associated with cardiac catheterization procedures include bleeding, allergic reaction to the X-ray contast agents used to visualize the coronary arteries, and myocardial infarction. Cardiac catheterization ( heart cath) is the insertion of a Catheter into a chamber or vessel of the Heart. Myocardial infarction ( MI or AMI for acute myocardial infarction) also known as a heart attack, occurs when the blood supply With PCI, the requirement for emergency CABG has markedly decreased since the days of balloon angioplasty, such that in some communities, coronary stenting is permitted in hospitals without on-site cardiac surgery facilities[18], though this remains highly controversial in the United States, including because of the rare but largely unpredictable risk of coronary artery perforation[4]. Rarely, a type of allergic reaction to the drug may occur; episodes of fatality have been reported. [19]

Stent thrombosis

Although drug-eluting stents were regarded as a major medical advance when they first appeared, new evidence suggests that they also put patients at risk for stent thrombosis, or the formation of a clot in the stent. Thrombosis is the formation of a blood Clot ( Thrombus) inside a Blood vessel, obstructing the flow of Blood through the Circulatory A stent is a foreign object in the body, and the body responds to the stent’s presence in a variety of ways. Macrophages accumulate around the stent, and nearby smooth muscle cells proliferate. Macrophages ( Greek: "big eaters" from makros "large" + phagein "eat" ( Mø) are cells within the tissues that These physiological changes, which can cause restenosis, are limited by the drugs released by the stent, but these drugs also limit re-endothelialization. Restenosis literally means the re occurrence of Stenosis. This is usually restenosis of an Artery, or other Blood vessel, but possibly This lack of healing can make the stent an exposed surface on which a life-threatening clot can form.


Though less frequent with drug-eluting stents, neointimal proliferation can still occur in DES and cause restenosis. Stent occlusion because of thrombosis may occur during the procedure, in the following days, or later. Thrombosis is the formation of a blood Clot ( Thrombus) inside a Blood vessel, obstructing the flow of Blood through the Circulatory Treatment with the antiplatelet drugs aspirin and clopidogrel appears to be the most important factor reducing this risk of thrombosis, and early cessation of one or both of these drugs after drug-eluting stenting markedly increases the risk of stent thrombosis and myocardial infarction. Aspirin, or acetylsalicylic acid (ASA (əˌsɛtɨlsælɨˌsɪlɨk ˈæsɨd is a Salicylate drug, often used as an Analgesic to relieve Clopidogrel is a potent oral antiplatelet agent often used in the treatment of Coronary artery disease, Peripheral vascular disease, and Cerebrovascular [20]

Whether drug-eluting stents are at higher risk than bare-metal stents for late thrombosis is intensely debated. [21] In meta-analyses of the sirolimus and paclitaxel-eluting stent trials, there was a small but statistically higher risk of thrombosis after the first year, compared to bare metal stents. In Statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses Late stent thrombosis often causes myocardial infarction and sometimes death. Myocardial infarction ( MI or AMI for acute myocardial infarction) also known as a heart attack, occurs when the blood supply [22] In other analyses, the late thrombosis risk is offset by drug-eluting stents' markedly reduced risk of restenosis and its complications including myocardial infarction. A meta-analysis concluded that the mortality risk associated with drug-eluting and bare-metal stents is similar. In Statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses [23]

Comparing different drug-eluting stents Whether sirolimus or paclitaxel-eluting stents are measurably different in their outcomes is a topic of great interest, including to the marketing departments of the manufacturers themselves. Analyses favoring one or the other stent have been advanced. The differences, if any, between the two devices are small. [24]

Design

Drug-eluting stents consist of three parts. The stent itself is an expandable metal alloy framework. A coating, typically of a polymer, elutes the drug into the arterial wall by contact transfer. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds In the polymer is the drug, which inhibits neointimal growth. Both sirolimus and paclitaxel were previously used for other medical applications; new drugs are being evaluated for coronary stents. [6]

Investigation and Alternative drugs

In place of the stainless steel currently used in stents, various biodegradable frameworks are under early phases of investigation. Since metal, as a foreign substance, provokes inflammation, scarring, and thrombosis (clotting), it is hoped that biodegradable or bioabsorbable stents may prevent some of these effects. A magnesium alloy–based stent has been tested in animals, though there is currently no carrier for drug elution. Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 [25] A promising biodegradable framework is made from poly-L-lactide, a polymer of a derivative of L-lactic acid. Lactic acid ( IUPAC Systematic name: 2-hydroxypropanoic acid) also known as milk acid, is a Chemical compound that plays a role One of these stents, the Igaki-Tamai stent, has been studied in pigs; tranilast[26] and paclitaxel[27] have been used as eluted drugs. Paclitaxel is a Mitotic inhibitor used in Cancer Chemotherapy.

There are also several other anti-proliferative drugs under investigation in human clinical trials. In general, these are analogues of sirolimus. Like sirolimus, these block the action of mTOR. Abbott has developed zotarolimus; unlike sirolimus and paclitaxel, this sirolimus analogue designed for use in stents with phosphorylcholine as a carrier. Abbott Laboratories ( is a diversified pharmaceuticals Health care company Phosphorylcholine is a molecule secreted by the Seminal vesicle which has a molecular weight of 184 Their ZoMaxx stent is a zotarolimus-eluting, stainless steel and tantalum–based stent; a modified phosphorylcholine slowly releases the zotarolimus. Tantalum (ˈtæntələm (formerly tantalium /tænˈtæliəm/ is a Chemical element with the symbol Ta and Atomic number 73 [28] Zotarolimus has been licensed to Medtronic which is researching the effectiveness in a drug-eluting stent of their own. Medtronic Inc ( based in Minneapolis Minnesota[http //wwwmedtronic Their Endeavor stent, which is a cobalt alloy,[6] also uses phosphorylcholine to carry the zotarolimus was approved for use in Europe in 2005 is now close to U. Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co. S. FDA approval. [29]

Clinical trials are currently examining two stents carrying everolimus,[6] an analog of sirolimus. Everolimus (RAD-001 (marketed as Certican by Novartis) is a derivative of Rapamycin (sirolimus and works similarly to Rapamycin as an mTOR Guidant, which has the exclusive license to use everolimus in drug-eluting stents, is the manufacturer of both stents. Guidant Corporation, part of Boston Scientific, designs and manufactures Artificial pacemakers implantable Defibrillators Stents and other cardiovascular The Guidant vascular business was subsequently sold to Abbott. [30] The Champion stent uses a bioabsorbable polylactic acid carrier on a stainless steel stent. [31][32] In contrast, its Xience stent uses a durable (non-bioabsorbable) polymer on a cobalt stent. [33]

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  32. ^ Guidant News Release — April 5, 2004. Guidant (2004-04-05). Guidant Corporation, part of Boston Scientific, designs and manufactures Artificial pacemakers implantable Defibrillators Stents and other cardiovascular "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Events 456 - St Patrick returns to Ireland as a missionary bishop Retrieved on 2007-07-23. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1632 - Three hundred colonists bound for New France depart from Dieppe France.
  33. ^ Guidant News Release — June 22, 2005. Guidant (2005-06-22). Guidant Corporation, part of Boston Scientific, designs and manufactures Artificial pacemakers implantable Defibrillators Stents and other cardiovascular Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 217 BC - Battle of Raphia: Ptolemy IV of Egypt defeats Antiochus III the Great of the Seleucid kingdom. Retrieved on 2006-07-23. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1632 - Three hundred colonists bound for New France depart from Dieppe France.

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