Cardiac Stent

A cardiac stent is a small tube that is used to widen arteries supplying the heart that have narrowed. Stents are often used in angioplasty, which is a procedure that improves blood flow through narrowed or blocked arteries. Stents help prevent arteries from becoming narrowed or blocked again in the months or years after angioplasty. Stents are also placed in a weakened artery to improve blood flow and to help prevent the artery from bursting. The meshwork of stents is usually made of metal, but sometimes a fabric is used. Fabric stents, also called stent grafts, are used in large arteries. Some stents are coated with medicines that are slowly and continuously released into the artery. These medicines help prevent the artery from becoming blocked again.

Taxus drug-coated stent. Source: U.S. Food and Drug Administration

Description

In the disease atherosclerosis, which is extremely common in developed nations, fatty material called plaque deposits on the inside walls of coronary arteries. The accumulation of plaque narrows the arteries and hinders blood flow. Smoking and some medical conditions such as diabetes and high cholesterol also promote plaque formation and narrowing of the arteries. The narrow arteries and consequent sluggish blood flow can cause chest pain (angina) and increase the risk of a heart attack.

To improve blood flow and reduce the risk of cardiac events, such as a heart attack, doctors perform an angioplasty. In this procedure, a doctor inflates a balloon inside the narrowed artery. The balloon pushes the plaque up against the blood vessel wall and restores blood flow to the heart.

Doctors usually place a stent in the treated portion of the artery during angioplasty if the artery is large enough. The stent supports the inner artery wall and reduces the chance of the artery closing up again.

Cardiac stents are also used for other conditions. Sometimes they are used to repair a torn aorta. The aorta is the large blood vessel that carries blood out of the heart and into the body’s other blood vessels. Blood can be forced into this tear, which widens the blood vessel. Eventually the artery may become blocked, or burst. This primarily occurs in the part of the aorta located in the chest. Fabric stents are being developed and used experimentally to prevent blood from flowing into the tear. A fabric stent placed within the torn area of the artery can help restore normal blood flow and reduce the risk of a burst aorta. Only a few hospitals offer this procedure. Stents are also used to repair aortic arteries that have bulges called aneurysms.

A cardiac stent can be used in arteries that are blocked 55% or more. Doctors perform various tests to determine if a stent is appropriate. The decision is ultimately left to the patient. Stents are used when lifestyle changes and medications do not reduce the amount of plaque in the arteries.

Types

• Drug-eluting stents: Some stents, called drug-eluting stents or DES, have coatings that slowly release drugs (eg. sirolimus, paclitaxel or everolimus) that reduce the unwanted growth of the artery wall tissue, therepy improving the chances that the artery will stay open. They can help the artery heal from the surgery and reduce the risk of future blockages.^[1]
• Bare metal stents: Sometimes bare metal stents are used without the drug coating. These are also effective in restoring blood flow. Bare metal stents are used in patients who cannot tolerate the medicine coating DES, as well as in some other situations.
• Fabric stents: Fabric stents are being developed to help reduce complications of a torn aorta. Currently, they are in the experimental stage.

Preparation

Some preparations may be necessary before stent surgery.

• The patient is given aspirin to reduce the chances of clotting.
• The patient fasts (doesn't eat or drink) for several hours.
• Some medications may need to be discontinued on the day of the procedure.

How Cardiac Stents are Placed

Cardiac stents are placed in the artery during an angioplasty. An angioplasty is performed with a flexible, plastic tube (catheter) that has a deflated balloon at the tip. The cardiac stent is wrapped around this balloon. In the procedure, a doctor makes a small opening in a blood vessel in the groin (upper thigh), arm, or neck. The catheter is thread into the blood vessel and up to the site of a blockage, aneurysm, or tear. X-ray “movies” are taken of the catheter as it moves into the blood vessel. This helps the doctor position the catheter. When the balloon is inflated, the stent is pushed against the artery wall and will remain there when the balloon is removed. Cells in the artery eventually grow to cover the mesh of the stent and create an inner layer that resembles what is normally seen inside a blood vessel.

This procedure usually takes a few hours and requires hospitalization.

Stent Placement. Source: National Heart, Lung, and Blood Institute

The illustration (above) shows the placement of a stent in a coronary artery. The coronary artery is located on the surface of the heart. Figure A shows the deflated balloon catheter and closed stent inserted into the narrowed coronary artery. The inset image on figure A shows a cross-section of the artery with the inserted balloon catheter and closed stent. In figure B, the balloon is inflated, expanding the stent and compressing the plaque to restore the size of the artery. Figure C shows normal blood flow restored in the stent-widened artery. The inset image on figure C shows a cross-section of the compressed plaque and stent-widened artery.

The animation below shows coronary angioplasty and stent placement.

A very narrow artery, or one that is difficult to reach with the catheter, may require more steps to place a stent. This type of artery usually is first expanded by inflating a small balloon. The balloon is then removed and replaced by another larger balloon with the collapsed stent around it. The stent is then placed according to the procedure above.

When angioplasty and stent placement are performed on carotid arteries, a special filter device is used. The filter helps keep blood clots and loose pieces of plaque from passing into the bloodstream and brain during the procedure.

Benefits

Stents can improve the outcome of an angioplasty by increasing blood flow and provide more nourishment to areas of the heart. This will also help prevent the heart from having to over work to pump blood.

In about 20% of cardiac stent placements, the artery narrows again within six months of the angioplasty. If an angioplasty is done without placing a stent, the risk of the arteries closing can be twice as high.

Risks

Complications

Complications can arise due to both the angioplasty and stent itself.

Complications related to angioplasty

Major complications from angioplasty and stent placement are rare. The most common complications of an angioplasty include the following:

• Bleeding from the site where the catheter was inserted into the skin
• Damage to the blood vessel from the catheter
• Infection
• Allergic reaction to the dye used during the procedure

Another common problem after angioplasty is excessive tissue growth within the treated portion of the artery. This can cause the artery to narrow or close again, which is called restenosis. With bare-metal stents, the incidence of restenosis may vary from 8% to as high as 80% at 6 months; the risk depends on both anatomic and clinical factors.^[2] The problem of restenosis is often avoided with the use of newer stents coated with medicines (drug-eluting stents) that help prevent this excessive growth. Treatment with radiation can also limit this growth. For this procedure, a doctor places a wire where the stent is placed. The wire releases radiation and stops cells around the stent from growing and blocking the artery. This procedure, involving intracoronary radiation, is known as brachytherapy.^[3]

The illustration shows the restenosis of a stent-widened coronary artery. In figure A, the expanded stent compresses plaque, allowing normal blood flow. The inset image on figure A shows a cross-section of the compressed plaque and stent-widened artery. In figure B, over time, the plaque grows through and around the stent, causing a partial blockage and abnormal blood flow. The inset image on figure B shows a cross-section of the growth of the plaque around the stent.

Another problem that can occur with stents is blood clot formation (thrombosis) occurring months to years after placement. This can occur with both drug-eluting and bare-metal stents.^[4]

Complications related to the stent

About 1%–2% of people with a stent develop a blood clot at the stent site. Blood clots can cause strokes, heart attacks, and other serious problems. The risk of blood clots is greatest during the first few months after the stent is placed in the artery.

Drug-coated stents may increase the risk of developing blood clots. The Food and Drug Administration has found no conclusive evidence that these stents increase the chances of having a heart attack or dying, if they are used as recommended.

Complications related to cardiac stents in the abdomen

Whenever an aneurysm in the abdomen region of the aorta is repaired with either surgery or with a fabric stent, few rare but serious complications can occur:

• burst artery (aneurysm rupture).
• Blocked blood flow to the stomach or lower body.
• Paralysis in the legs due to interruption of blood flow to the spinal cord. This is an especially rare complication.

Another possible complication is the fabric stent moving further down the aorta. This sometimes happens years after the stent is first placed. Such stent migration may require a doctor to place another fabric stent in the area of the aneurysm.

Precautions after a stent procedure

Medicines such as clopidogrel are usually used for at least a few months after the procedure to help prevent blood clots from forming within the stents. Intense exercise is discouraged following the procedure.

Metal stents preclude patients from having a magnetic resonance imaging (MRI) test within the first few months following the procedure. Metal detectors used in airports and other screening areas don’t affect stents. Imaging tests, such as x-rays, are sometimes used to monitor the placement of fabric stents.

Recovery

Immediately after stent implantation and removal of the catheter, the tube insertion site is bandaged. A small sandbag or other type of weight may be put on top of the bandage to apply pressure to help prevent bleeding. Nurses monitor the closure site for bleeding, and sometimes a small bruise or small, hard “knot” develops.

Some serious complications that occur shortly after the procedure include the following:

• Constant or large amount of bleeding at the site that can’t be stopped with a small bandage.
• Unusual pain, swelling, redness, or other signs of infection at or near the catheter insertion site.

Clinical Trials

For a list of American government-sponsored clinical trials investigating cardiac stents, click here.

References

1. ↑ Roiron C, Sanchez P, Bouzamondo A, Lechat P, Montalescot G. Drug eluting stents: an updated meta-analysis of randomised controlled trials. Heart. 2006 May;92(5):641-9. Abstract | Full Text | PDF
2. ↑ Sousa JE, Costa MA, Tuzcu EM, Yadav JS, Ellis S. New frontiers in interventional cardiology. Circulation. 2005 Feb 8;111(5):671-81. Citation | Full Text | PDF
3. ↑ Bhargava B, Karthikeyan G, Abizaid AS, Mehran R. New approaches to preventing restenosis. BMJ. 2003 Aug 2;327(7409):274-9. Citation | Full Text | PDF
4. ↑ Serruys PW, Daemen J. Are drug-eluting stents associated with a higher rate of late thrombosis than bare metal stents? Late stent thrombosis: a nuisance in both bare metal and drug-eluting stents. Circulation. 2007 Mar 20;115(11):1433-9. Citation | Full Text | PDF