Stent: advances and clinical applications

A stent is a small medical device in the shape of a tube that is used to keep blood vessels or airways open. Its main function is to improve or restore blood flow or air circulation in the body. Here are some key features and common uses of stents:

Material

Stents can be manufactured using various materials, and the choice of material often depends on the specific application and the required properties. Here is a more detailed description of the materials commonly used in stent manufacturing:

1. Metal (Nickel-Titanium Alloys and Stainless Steel): Many stents are made from nickel-titanium alloys (nitinol) or stainless steel. Nitinol is known for its ability to return to its original shape after deformation and for being highly resistant to corrosion. Stainless steel is also used due to its durability and strength. These metals are especially useful in applications where flexibility and expansion capability are required, such as in coronary stents.
2. Polymers: Some stents are made from biocompatible polymers, such as polylactic acid (PLA) or polyethylene. Polymer stents are lighter and more flexible compared to metallic ones, and they are used in specific applications, such as in biliary stents.
3. Drug-eluting stents: These stents are made with materials that allow the controlled release of medications. The drug layer is applied to the surface of the stent and is gradually released over time. This helps prevent the recurrence of obstruction by inhibiting scar tissue growth or plaque formation.
4. Eluting vs. Bare-Metal: Stents can be “eluting” (drug-releasing) or “bare-metal” (without coating). Eluting stents are especially effective in preventing restenosis (re-narrowing of the artery) by releasing anti-inflammatory or antiproliferative drugs.
5. Biomaterials: Biomaterials are being explored for stent manufacturing, especially those that can better integrate with surrounding tissues. These biomimetic stents aim to improve biocompatibility and reduce the inflammatory response.

The choice of material will depend on various factors, including the location of the stent in the body, the degree of flexibility required, the durability needed, and the expected biological response. Each material has its own advantages and disadvantages, and advances in stent technology continue to explore new options to improve the efficacy and safety of these medical devices.

Shape and structure of a stent

The shape and structure of stents are crucial aspects for their function and effectiveness in the treatment of vascular diseases. Here is a more detailed explanation of the typical shape and structure of stents:

1. Stent shape:
   • Tube: Most stents are tube-shaped. This tubular form is essential to allow the stent to expand and adapt to the diameter of the blood vessel or airway where it is implanted.
   • Conformability: Stents are designed to be conformable, meaning they can adjust to various shapes and sizes. This is especially important in areas where blood vessels or airways may have curves or bifurcations.
2. Mesh or interwoven structure:
   • Mesh design: Most stents have a mesh or interwoven structure that can be expanded. This mesh provides structural support to the blood vessel or airway, maintaining the opening after balloon dilation.
   • Mesh spacing: The spacing between the mesh struts can vary. Denser spacing may provide greater support, while wider spacing can allow the flexibility and permeability needed for the surrounding tissue.
3. Radiopaque markers:
   • Inclusion of markers: Many stents include radiopaque markers, small metallic elements that are visible on X-ray images. These markers help physicians visualize and precisely place the stent during the procedure.
4. Delivery system:
   • Delivery system: Stents can have different deployment systems. Some are deployed by inflating a balloon (stent angioplasty), while others can be self-expanding and return to their original shape without the need for a balloon.
5. Length and diameter:
   • Variety of sizes: Stents are available in different lengths and diameters to adapt to the specific needs of each patient and to the characteristics of the lesion or narrowing in the artery or airway.

The combination of tubular shape, mesh structure, and specific materials ensures that the stent can fulfill its function of keeping the blood vessel or airway open while minimizing irritation or the body’s immune response. These features allow for improved blood or air flow and ultimately support the patient’s recovery.

Stent implantation

Stent implantation is a medical procedure called angioplasty, which is performed to treat the obstruction of blood vessels or airways. Here is a general description of the stent implantation process:

Patient preparation

• Before the procedure, the patient may receive specific instructions, such as refraining from eating or drinking for a certain period of time.
• Local or general anesthesia will be administered, depending on the type of procedure and the location of the stent.

Access to the artery or airway

• A small incision or puncture is made in the area of the body where access to the blood vessel or airway will be obtained.
• In some cases, the femoral artery (in the groin) or the radial artery (in the wrist) may be used as access points.

Catheter insertion

• A thin, flexible catheter is inserted through the incision and guided to the affected area using real-time X-ray imaging.
• The catheter has an end that contains a balloon and, in some cases, a stent.

Catheter positioning

Balloon inflation

Once the catheter is in position, a balloon at the tip of the catheter is inflated. The balloon exerts pressure on the plaque or obstructive material, compressing it against the walls of the blood vessel or airway.

Stent implantation

• In some cases, a stent can be implanted during angioplasty. The stent is placed in the dilated area and expanded to keep the artery or airway open.
• Some stents are self-expanding, while others require balloon inflation to expand.

Catheter removal

• After completing the angioplasty and, if necessary, the stent implantation, the catheter is removed.
• The incision may be closed with sutures or by using percutaneous closure devices.

Monitoring and recovery

• The patient is monitored after the procedure to detect possible complications.
• Recovery may vary depending on the complexity of the procedure and the patient’s overall health.

This procedure has proven to be effective in treating obstructions of the coronary arteries, peripheral arteries, and other areas of the vascular or respiratory system. However, as with any medical procedure, there are risks and benefits, and the decision to perform angioplasty with stent placement will be based on the physician’s assessment according to the patient’s needs and condition.

Medical applications of a stent

Stents have various medical applications and are used in different areas of the body to treat or prevent obstructions in blood vessels and airways. Here are some of the most common medical applications of stents:

Coronary arteries

Stents are widely used to treat coronary artery disease. They are implanted in the coronary arteries of the heart during angioplasty procedures to keep obstructed arteries open and restore blood flow.

Peripheral arteries

In peripheral arteries, such as those in the legs, stents are used to treat peripheral artery disease. They help improve blood flow and relieve associated symptoms, such as pain and intermittent claudication.

Biliary ducts

Stents are placed in the biliary ducts to treat obstructions and improve bile flow. This procedure is often performed in cases of pancreatic or biliary tract cancer, as well as in cases of benign biliary stricture.

Urinary tract

In the urinary system, stents are used to treat obstructions in the ureters. These stents, often temporary, help maintain urine flow from the kidneys to the bladder.

Cerebral blood vessels

Some stents are used in cerebral arteries to treat aneurysms or vascular malformations. These cerebral stents can help maintain the integrity of the blood vessel and prevent complications.

Trachea and bronchi

In the respiratory system, stents are used in the airways to treat narrowings or collapses. These airway stents help maintain airway patency.

Arteriovenous fistulas

Stents can also be used to treat abnormal arteriovenous fistulas. They may be necessary in patients with kidney disease who require dialysis.

Drug-eluting stents

Drug-eluting stents are used in various applications, including those mentioned above. These stents release medications directly into the surrounding area to prevent the recurrence of obstruction.

Interventional cardiology

In addition to the specific application of stents, interventional cardiology includes other procedures such as coronary angioplasty, where stents play a fundamental role.

It is important to note that the specific application of stents will depend on the patient’s medical condition and the healthcare professional’s assessment. Each type of stent and procedure is selected based on the location and severity of the obstruction, as well as other relevant medical factors.

Conclusion

In summary, stents are essential medical devices used in a variety of applications to treat obstructions in blood vessels and airways. Their tubular shape, mesh or interwoven structure, and specific materials allow these devices to be precisely implanted during procedures such as angioplasty. From the treatment of cardiovascular diseases to improving flow in peripheral arteries, biliary ducts, and more, stents play a fundamental role in modern medicine.

The wide range of medical applications of stents highlights their versatility and ability to address a broad spectrum of clinical conditions. Furthermore, the evolution of stent technology, such as the development of drug-eluting stents, continues to improve the effectiveness of these devices and reduce complication rates. The decision to use a stent in a specific patient is based on the detailed assessment of the healthcare professional, taking into account the medical condition, the location of the obstruction, and other relevant factors to ensure effective and safe treatment.

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