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A stent is a stent made of metal or synthetic fibers, which is used in vessels or hollow organs to support and keep them open. Mostly it is a tubular, small lattice framework.
A stent is always used when a permanent dilation of a closed vessel or hollow organ can not be guaranteed by a mere dilatation of the vessels (percutaneous transluminal angioplasty, PTA).
Most often this is with:
- Narrowing of the coronary arteries in coronary heart disease (CHD).
- Circulatory disorders in the arm and leg arteries in peripheral arterial disease (PAOD).
- Stroke in narrowing of carotid arteries (carotid stenosis).
- Extension of the main artery (aortic aneurysm).
- Narrowing of the renal arteries (renal artery stenosis).
- Narrowing of aisles (e.g., bile duct stenosis).
A stent stabilizes narrowed vessels after their expansion. The goal is to prevent a new vascular occlusion. In addition, the metal or synthetic stent fixes vascular deposits, smooths the surface of the vascular space by pressing it against the vascular wall, thereby improving blood flow in the vessel. The most common variant is the "cardiac stent" on the coronary arteries, which is used in patients with coronary heart disease. Here, the stent has now replaced the bypass operation. With the aid of a thin plastic tube (catheter), the surgeon places the stent, which can be compressed tightly by its fine-meshed grid structure. There are different types.
The self-unfolding stent consists of a steel grid mesh and is surrounded by a plastic cover. After the surgeon has inserted it through the catheter into the vasoconstriction, he pulls back the sheath and the stent unfolds.
The folded stent is placed on a so-called balloon catheter, which can be inflated as part of a vascular dilation, the so-called percutaneous transluminal angioplasty (PTA). The metal mesh of the stent then retains the expanded shape.
In addition to uncoated stents (bare metal stents, BES), drug-coated stents (drug eluting stent, DES) are now being used more and more frequently. The released drugs prevent new cell formation and thus counteract reocclusion (restenosis). In the meantime, doctors are also using completely resorbable stents ("bioabsorbable vascular scaffolds", BVS), which break down over a period of twelve to 18 months.
The use of a stent as a life support measure is becoming increasingly important. The possibilities for improving the quality of life are very high, and the use of a stent in medicine is versatile.
Stent is used to keep open and to expand vessels and hollow organs. Strictly speaking, a stent stabilizes vessels after they have expanded, especially on the coronary arteries. In general, a stent consists of a so-called spiral wire prosthesis made of metal and / or synthetic fibers.
Cardiologist Ulrich Sigwart develops the stents that are common today. However, it should take a few decades before the German cardiologist Ulrich Sigwart succeeded in developing and using the stents that are common today. He did not let go of the problem of vascular occlusion after heart surgery and the risk of the time-consuming bypass surgery that was customary at the time, and he developed the stents that are now world-famous.
The work of cardiologist Andreas Grüntzig in Zurich in the 1970s was also groundbreaking. He developed the balloon catheter method to reopen closed or narrowed arteries. Building on this, Ulrich Sigwart first used a metal stent on a patient in 1986. At that time he received a lot of criticism for his procedure, which, in contrast to the riskier bypass operations, was mostly without complications. The Fima Medinvent from Lausanne then developed a fine grid tube together with Ulrich Sigwart, which was subsequently further developed. There are different types of stents today, and stent surgery has become routine.
In Germany, fewer people have to go to hospital because of coronary artery disease because these patients are more and more often being treated by coronary arteries. Extrapolated to the population of Germany, doctors performed a total of more than 435,000 bypass operations in 2018, implanted stents, or expanded blocked vessels using balloon dilation. This corresponds to a rate of 42 percent of all patients who are treated for ischemic heart disease in the hospital. In 20015 it was 36.6 percent.
Stents: Types, Materials and Manufacture
One distinguishes between
- self-expanding stents,
- balloon expanding stents,
- coated stents as well,
- bioresorbable stents,
whereby there are different types of the individual classes. In technical terms, coated (drug eluting stents, also called DES) and uncoated stents (bare mental stents, also called BES) are often spoken. Recently, resorbable stents (BVS stands for bioabsorbable vascular scaffold) are becoming increasingly important.
The metal grid tube has been used frequently from the 1980s to the 1990s. In the beginning, a stent that was inserted coronary consisted only of an alloy of stainless steel. This is still the simple, classic, and uncoated shape.
The self-expanding stent consists of a steel mesh that is encased in plastic. After the surgeon uses the catheter to insert the stent into the vasoconstriction, the plastic sheath is withdrawn and the stent can deploy properly.
In the balloon-expanding stent, the stent is placed on a balloon catheter which is inserted and inflated during a vasodilator operation - this is a translucent angioplasty, or PTA for short - in technical terms. The expanded shape of the metal braid is maintained and the catheter is pulled out again. As a result, the stent grows into the vessel. This form has been common since 1989.
However, when it became increasingly common to find that inflammation developed around the stents or that a new stenosis (this is further narrowing or occlusion due to deposits such as blood clots or arterial calcification) proliferated, so-called coated stents were developed. These stents, also called special stents or DES for short, are coated with medications that pass on their active ingredients to the surrounding cells and are therefore beneficial for the ingrowth of the stent and prevent re-closure (restenosis).
A distinction is made between the following types of coated stents
- antibody-coated stents (healing stents)
- drug eluting stents (DES)
- radioactive stents
In the so-called "drug eluting stents", the immunosuppressant sirolimus and the cancer therapeutic paclitaxel have proven to be effective. Antibody-coated stents primarily prevent the risk of thrombosis after surgery. Since 1992, stents have also been subjected to deuteron bombardment or have been implanted directly as radioisotopes, also known as ion implantation. The point and benefit here is to prevent overgrowth of cell growth in the inner skin vessels. However, radioactive stents are hardly used in Germany.
In 2012, so-called resorbable stents were developed and used for the first time, which will dissolve on their own, depending on the medical need. The idea is that the vessel only has to be supported for a while and that a stent is always a foreign body that can cause complications in the long term.
These so-called bio-stents come in different types, and research on them is far from complete. Here, materials are used which also play a role in the body's metabolism, such as metallic glass, alloys made of magnesium and zinc or rare earth metals; furthermore lactic acid polymers, which remain as supports for about three to six months and then decompose into water and carbon dioxide within two years.
However, bio-stents have been criticized in the past. According to studies, they should lead to stent thrombosis more frequently; The magnesium alloy in particular has proven to be disadvantageous. Abbott has even withdrawn its bio-stents and patients with a bio-stent have to see their doctor regularly. The topic of bio stents went through the Swiss press in 2017. Publications such as the Luzerner Zeitung, the Tagesanzeiger, but also the renowned NZZ report on the problem and support their theses with references to studies.
Areas of Application of Stents
Stents are used for all complaints in which vasoconstriction or vascular occlusion is the cause. This can be caused by hardening of the arteries (arteriosclerosis) or a platelet plug (thrombosis). If the platelets detach from the wall of the vessel and block narrower vessels, this is called an embolism. Improper nutrition, which leads to high blood lipid levels, lack of exercise, obesity, high blood pressure, smoking as well as sometimes grief, worries and fears that can be "on the heart" are responsible for the deposits and blockages in the vessels.
Due to the narrowing and blockage of the vessels, the blood flow can no longer flow properly, which can result in a stroke and a heart attack. It is mainly the coronary arteries in which the so-called coronary stents are used. But the following vessels and hollow organs also need to be kept open and supported by stents in the event of symptoms:
- Arm and leg arteries (peripheral arterial disease)
- Aorta (with an aneurysm)
- Renal artery narrowing (renal arteriostenosis)
- Carotid artery narrowing (carotid stenosis)
- Narrowing of the bile ducts (bile duct stenosis)
- Eye: With stent implants, the intraocular pressure is reduced by the drainage of the aqueous humor
Stents are also used in cancer therapy. With organ narrowing and relocation due to tumor formation. By the way, a completely different application comes from Japan: a nasal stent that is supposed to help against snoring and breathing interruptions.
Stent Implantation Procedure
Stent implantation is similar to PTCA or cardiac catheterization. Because it is a minimally invasive procedure, only small steps are necessary. Before the stent is placed, some routine examinations take place, such as a blood analysis or an EKG (electrocardiogram). In the case of a closed coronary artery, an exercise ECG, a myocardial scintigram and X-ray examinations of the heart and lungs are also carried out. Before the procedure, the patient receives a local anesthetic at the catheter access area.
The first step in stent implantation is the creation of an external access. For this purpose, the doctor inserts a cannula into a vessel that is close to the surface. Under X-ray control, a guide catheter is then advanced towards the narrow point of the affected vessel. The doctor then places the stent at this point.
A folded balloon is attached to the front tip of the catheter as part of a PTA. Upon arrival at the constriction, the balloon is expanded, causing the calcifications to press against the wall of the vessel so that the vessel can be opened. The balloon-expanding stent is expanded at the same time. In this way, a further vascular occlusion can be prevented. After deflating the balloon, the doctor pulls the catheter out of the body. In contrast, the stent remains in the vessel and keeps it open.
Risks Associated With Stent Implantation
During the procedure it can be too
- Hypersensitivity to the contrast medium,
- a stent thrombosis, where a blood clot immediately clogs the stent,
- a heart attack,
- allergic reactions,
- an increased risk of bleeding when anticoagulant drugs are administered,
- vascular injuries or
- injuries and closure of the trachea.
come. Speaking of allergies: Because of her allergy to certain metals, a Munich-based woman was used in 2016 to have the world's first fully degradable magnesium stent.
After Stent Surgery
Of course, the doctor will clarify the patient's medication and the psychological stress of an operation beforehand. Blood-thinning medication must be taken after surgery, and an all-round examination will be necessary after a few weeks. In itself, the placement of a stent does not affect the daily routine. The patient generally feels freer and more comfortable. The abstinence from tobacco, a wholesome, balanced diet and physical activity are beneficial.
However, one should know that a stent is always a foreign body. Therefore, after a stent operation, the formation of blood clots is prevented by a dual inhibition of platelet aggregation. Another risk is the formation of new connective tissue, the so-called restenosis, which can be prevented by coated, drug-releasing stents.
On the other hand, uncoated stents are recommended for all patients who have several diseases and those who are seriously ill with increased medication, as this can lead to side effects and side effects.
Manufacture And Supplier of Stents
There are differences between the manufacturers in the manufacture, design and alloy of the stents. Medtronic offers a cobalt-nickel alloy instead of pure steel. Other producers rely on a cobalt-chrome alloy. The majority of all stents that are used and offered today are drug-coated stents - such as the drug-releasing stents from Boston Scientific. There are numerous stent suppliers on the market. The biggest are
- Boston Scientific
- B. Braun
Optimed offers a unique beveled design. Self-sustaining stents, also known as self-expanding or peripheral stents, are often made with a nickel-titanium alloy (Nitinol). They are easier to shape, but not to be used by people with an allergy to nickel. Some manufacturers, such as the Pforzheim company Admedes Schuessler, have specialized in this type of stent. They are cut from nitinol tubes using lasers or braided from nitinol wires. The filigree lattice structures of the stents are sometimes only 0.5 mm thick and have wall thicknesses in the micrometer range. The high expectations for the bioabsorbable stents were not met. Abbott even removed its stent absorbent from the market in 2017.