Medical implant
A drug-eluting stent (DES) is a tube made of a mesh-like material used to treat narrowed arteries in medical procedures both mechanically (by providing a supporting scaffold inside the artery) and pharmacologically (by slowly releasing a pharmaceutical compound). A DES is inserted into a narrowed artery using a delivery catheter usually inserted through a larger artery in the groin or wrist. The stent assembly has the DES mechanism attached towards the front of the stent, and usually is composed of the collapsed stent over a collapsed polymeric balloon mechanism, the balloon mechanism is inflated and used to expand the meshed stent once in position. The stent expands, embedding into the occluded artery wall, keeping the artery open, thereby improving blood flow. The mesh design allows for stent expansion and also for new healthy vessel endothelial cells to grow through and around it, securing it in place.
A DES is different from other types of stents in that it has a coating that delivers medication directly into the blood vessel wall. The stent slowly releases a drug to prevent the growth of scar tissue and new obstructive plaque material which caused the original blood vessel stenosis, this clogging of a stent is termed restenosis. A DES is fully integrated with a catheter delivery system and is viewed as one integrated medical device.
DESs are commonly used in the treatment of narrowed arteries in the heart (coronary artery disease), but also elsewhere in the body, especially the legs (peripheral artery disease). Over the last three decades, coronary stenting has matured into a primary minimally invasive treatment tool in managing CAD. Coronary artery stenting is inherently tied to percutaneous coronary intervention (PCI) procedures. PCI is a minimally invasive procedure performed via a catheter (not by open-chest surgery), it is the medical procedure used to place a DES in narrowed coronary arteries. PCI procedures are performed by an interventional cardiologist using fluoroscopic imaging techniques to see the location of the required DES placement. PCI uses larger peripheral arteries in the arms or the legs to thread a catheter/DES device through the arterial system and place the DES in the narrowed coronary artery or arteries. Multiple stents are often used depending on the degree of blockage and the number of diseased coronary arteries that are being treated.
Design.
A drug-eluting stent (DES) is a small mesh tube that is placed in the arteries to keep them open in the treatment of vascular disease. The stent slowly releases a drug to block cell proliferation (a biological process of cell growth and division), thus preventing the arterial narrowing (stenosis) that can occur after stent implantation. While such stents can be used in various arteries throughout the body, they are commonly placed in the coronary arteries to treat coronary heart disease. DES products are integrated medical devices and are part of a percutaneous coronary intervention (PCI) delivery system.
DES is a medical device with several key properties: it functions as a structural scaffold, physically keeping an artery open to ensure blood flow; the device has specific drug delivery features, and the chosen drug is critical for its effectiveness. The drug, the hallmark compenent of the device, is selected for its suitability in inhibiting restenosis and its pharmacokinetics. Apart from the drug, the materials used in the fabrication of the device are also essential and are carefully chosen for their biocompatibility and durability in a biological environment, such as human blood; these materials must also withstand the constant motion of the heart's beat and be suitable for future patient imaging using magnetic resonance imaging (MRI) technologies, which employ high magnetic fields.
Other components, such as the catheter design, also play significant roles in the device's overall functionality and effectiveness.
DES are typically composed of metal alloys, most commonly stainless steel or cobalt-chromium, but can also be made of other materials such as platinum-chromium or nickel-titanium. The stent is often coated with a polymer to control the release of drugs. The role of polymers in drug delivery is significant as they regulate the rate at which the drug is released into the surrounding tissue. There are also polymer-free stents where the drug is directly coated on the stent or contained in reservoirs within the stent.
The design of the stent includes struts, which are thin wire structures that make up the stent frame. The strut thickness can influence the stent's performance, with thinner struts generally being associated with lower restenosis rates and reduced thrombosis risk.
Most DES are balloon-expandable, meaning they are mounted on a balloon catheter and expand when the balloon is inflated. There are also self-expanding stents, which automatically expand when deployed. The very first stent, introduced in 1986, was of this type.
The stent tube mesh is initially collapsed onto the catheter—in this collapsed state, it is small enough to be passed though relatively narrow arteries and then expanded in its destination place, pushing firmly to the diseased artery wall.
The pharmaceutical compounds that DES emit are antiproliferative agents such as sirolimus, everolimus, zotarolimus, paclitaxel and biolimus. These drugs help prevent the arterial narrowing that can occur after stent implantation. These drugs are also used for other purposes, that involve moderating the immune system or treating cancer. They work by inhibiting cell growth. In DES, they are used in very small amounts and for a short time, and only in the area where the stent is placed.
There is a distinction between coronary stents and peripheral stents. While both are used to prevent the narrowing of arteries, coronary stents are specifically for the coronary arteries, while peripheral stents are for any other arteries in the body. Peripheral stents are mostly bare metal ones; some peripheral DES, of the self-expanding type, are used in arteries of the legs.
Bioresorbable DES are made of materials that can be absorbed by the body over time, potentially reducing potential long-term complications associated with permanent stents.
Uses.
Atherosclerosis: a general background.
Atherosclerosis is a chronic disease that affects the large and medium-sized arteries. It is characterized by the accumulation of calcium, fats (such as cholesterol) and other substances in the innermost layer of the endothelium, a layer of cells that line the interior surface of blood vessels. Atherosclerosis is considered to be the most common form of arteriosclerosis, which refers to the loss of arterial elasticity caused by thickening and stiffening of blood vessels.
Atherosclerosis can begin as early as childhood with the development of small "fatty streaks" within arteries. These streaks are essentially deposits of fat. Over time, these initial lesions grow larger and become thicker, forming atheromas (atherosclerotic plaques).
Drug-eluting stents (DESs) are used in the treatment of atherosclerosis in both coronary interventions and peripheral arterial interventions:
DESs are used in the management of atherosclerosis in both coronary and peripheral arterial interventions. They help improve blood flow and reduce the risk of restenosis, thereby improving patient outcomes. The use of DESs is accompanied by appropriate medical therapy and lifestyle modifications to manage atherosclerosis effectively.
Stenosis and restenosis of blood vessels.
Stenosis of blood vessels refers to the narrowing of the blood vessels, which can restrict blood flow to the organs and tissues. This condition is often caused by the buildup of fatty deposits in the arteries, a process also called atherosclerosis.
In the context of stents, stenosis is a significant concern. Stents are inserted into a narrowed artery during a procedure known as angioplasty. The stents help to open up the narrowed artery and improve blood flow. However, over time, the treated artery can close up again, a condition known as restenosis.
Restenosis, or in-stent restenosis, is a blockage or narrowing that comes back in the portion of the artery previously treated with a stent. Restenosis tends to happen three to six months after the procedure. Restenosis is even more likely to occur if a stent would not have been used.
When restenosis occurs, another procedure may be needed to correct the problem, such as the placement of a DES that gradually release a drug compound that suppresses cellular growth, thereby reducing the potential for blockage within the stent area itself. This therapy significantly reduces the occurrence of adverse events post-stenting.
Technically, a DES in a mesh tube implant devices that is used in angioplasty procedures to treat stenosis of blood vessels and prevent restinosis: the stent, which elutes drugs, is implanted into the blood vessel to help keep the vessel open and improve blood flow. Specifically, drug-eluting stents are used in the treatment of various medical conditions usually at the site of stenotic or occlusive arterial lesions, but one of the primary medical uses is in the treatment of coronary artery disease. Stents are inserted into narrowed coronary arteries, where the narrowing is primarily caused by atherosclerosis. Stents are then expanded to open up the narrowed artery. Such stents gradually release a drug compound that suppresses cellular growth, into the newly stented area, thereby reducing the potential for blockage within the stent area itself. Such blockage is termed in-stent restenosis (ISR). This in-stent blockage is most often caused by excessive cell proliferation or thrombi (blood clots). Anticoagulation therapy (blood thinners), has become a standard treatment following the placement of DES. This therapy significantly reduces the occurrence of adverse events post-stenting.
Coronary interventions.
DESs have played a transformative role in the management of coronary artery disease. These stents are tiny, flexible mesh tubes employed during percutaneous coronary intervention (PCI) to address narrowed coronary arteries. What sets them apart is their special coating, which incorporates a drug delivery system that enables controlled release of medication over a specific period, typically within the first 30 to 45 days following implantation. This medication aids in inhibiting the formation of scar tissue within the stent and subsequent re-narrowing of the blood vessel.
PCI is a minimally invasive procedure. It involves the placement of a drug-eluting stent (DES) in a coronary artery. This procedure, previously known as angioplasty with a stent, is considered non-surgical as it is performed through a small puncture in a peripheral artery, avoiding the need to open the chest wall. While bleeding from the puncture site was once a concern, advancements in PCI practices have mitigated this issue through the use of pressure bands and arterial closure systems. Modern DES/PCI procedures are generally painless, although some mild discomfort may be experienced. In PCI, multiple DES are sometimes implanted within a single patient; the decision to use multiple stents is typically contingent on the extent of the coronary artery disease present and the number of diseased coronary arteries that require treatment.
Peripheral arterial interventions.
DESs have emerged as the primary therapeutic approach for managing symptomatic peripheral arterial disease (PAD). These specialized stents are now widely utilized in the treatment of peripheral arterial occlusive disease (PAOD), a condition that shares similarities with coronary artery disease but affects the peripheral arteries. By deploying DESs, healthcare professionals can effectively address and alleviate the complications associated with PAOD, enhancing patient outcomes and quality of life. The use of DESs in peripheral arterial interventions has shown encouraging results in terms of primary patency (PP) and target lesion revascularization (TLR) compared with bare-metal stents (BMSs).
Different types of DESs are available on the market, each with different concentrations of drugs and showing varying efficacy. Among the different DESs, sirolimus-eluting stents and everolimus-eluting stents were found to be more effective than paclitaxel-eluting stents.
Clinical indications.
PCI and stent placement are considered when someone shows signs of reduced blood flow in the arteries that supply the heart or when tests, such as different types of coronary artery imaging, show a blockage in those arteries.
Symptoms can include:
In a medical setting, it's not very useful for doctors to rely solely on what people say about where their pain comes from or how it feels, because the way people describe chest pain caused by reduced blood flow to the heart can vary greatly and may not match what is typically taught in medical education or described in books and articles.
Contraindications.
DES is not recommended in some cases as it may do more harm than good. DES is not suitable:
Bleeding disorders make DES unsuitable because of the need for anticoagulation drugs (blood thinners) during the procedure and in post-stenting aftercare. Other factors that could rule out the use of stents include a history of in-stent blockage, bleeding problems, complex or unsuitable coronary anatomy, or a short life expectancy due to other serious medical conditions.
Risks and complications.
Risks from the procedure.
Stent placement risks include bleeding, allergic reactions