Stenosis refers to narrowing or blockage of an artery due to buildup of a fatty substance called plaque (atherosclerosis). When it happens in the heart’s arteries (coronary arteries), it’s called coronary artery stenosis.

Restenosis (“re” + “stenosis”) is when a part of the artery that was previously treated for blockage becomes narrow again.

In-stent restenosis (ISR)

Angioplasty, a type of percutaneous coronary intervention (PCI), is a procedure used to open up blocked arteries. During the procedure, a small metal scaffold, called a cardiac stent, is almost always placed in the artery where it was reopened. The stent helps keep the artery open.

When a part of an artery with a stent gets blocked, it’s called in-stent restenosis (ISR).

When a blood clot, or thrombus, forms in a part of an artery with a stent, it’s called an in-stent thrombosis (IST).

Restenosis, with or without a stent, occurs gradually. It won’t cause symptoms until the blockage is bad enough to keep the heart from getting the minimum amount of blood it needs.

When symptoms do develop, they’re usually very similar to the symptoms the original blockage caused before it was fixed. Typically these are the symptoms of coronary artery disease (CAD), such as chest pain (angina) and shortness of breath.

IST usually causes sudden and severe symptoms. The clot usually blocks the entire coronary artery, so no blood can get to the part of the heart it supplies, causing a heart attack (myocardial infarction).

In addition to the symptoms of a heart attack, there may be symptoms of complications like heart failure.

Balloon angioplasty is the procedure used to treat coronary stenosis. It involves threading a catheter into the narrowed part of the coronary artery. Expanding the balloon on the catheter’s tip pushes the plaque to the side, opening the artery.

The procedure damages the artery’s walls. New tissue grows in the injured wall as the artery heals. Eventually, a new lining of healthy cells, called endothelium, covers the site.

Restenosis happens because the elastic artery walls tend to slowly move back in after being stretched open. Also, the artery narrows if tissue growth during healing is excessive.

Bare metal stents (BMS) were developed to help resist the reopened artery’s tendency to close while healing.

The BMS is placed along the artery wall when the balloon is inflated during angioplasty. It prevents the walls from moving back in, but new tissue growth stills occur in response to the injury. When too much tissue grows, the artery starts to narrow, and restenosis can occur.

Drug-eluting stents (DES) are now the most commonly used stents. They’ve significantly reduced the problem of restenosis, as seen by the restenosis rates found in a 2009 article published in American Family Physician:

  • balloon angioplasty without stent: 40 percent of patients developed restenosis
  • BMS: 30 percent developed restenosis
  • DES: under 10 percent developed restenosis

Atherosclerosis can also cause restenosis. A DES helps prevent restenosis due to new tissue growth, but it doesn’t affect the underlying condition that caused stenosis in the first place.

Unless your risk factors change after stent placement, plaque will continue to build up in your coronary arteries, including in stents, which can lead to restenosis.

A thrombosis, or blood clot, can form when clotting factors in the blood come in contact with something that’s foreign to the body, such as a stent. Fortunately, according to the National Heart Lung and Blood Institute, IST develops in only about 1 percent of coronary artery stents.

Restenosis, with or without stent placement, typically shows up between three and six months after the artery is reopened. After the first year, the risk of developing restenosis from excess tissue growth is very small.

Restenosis from underlying CAD takes longer to develop, and most often occurs a year or more after the original stenosis is treated. The risk of restenosis continues until the risk factors for heart disease are reduced.

According to the National Heart, Lung, and Blood Institute, most ISTs occur in the first months after stent placement, but there is a small, but significant, risk during the first year. Taking blood thinners can reduce the risk of IST.

If your doctor suspects restenosis, they’ll typically use one of three tests. These tests help to get information about the location, size, and other characteristics of a blockage. They are:

  • Coronary angiogram. Dye is injected into the artery to reveal blockages and show how well the blood flows on an X-ray.
  • Intravascular ultrasound. Sound waves are emitted from a catheter to create an image of the inside of the artery.
  • Optical coherence tomography. Light waves are emitted from a catheter to create high-resolution images of the inside of the artery.

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Restenosis that doesn’t cause symptoms usually doesn’t need any treatment.

When symptoms do appear, they usually gradually worsen, so there’s time to treat the restenosis before the artery completely closes and causes a heart attack.

Restenosis in an artery without a stent is usually treated with balloon angioplasty and DES placement.

ISR is usually treated with the insertion of another stent (usually a DES) or angioplasty using a balloon. The balloon is coated with medication used on a DES to inhibit tissue growth.

If restenosis continues to happen, your doctor may consider coronary artery bypass surgery (CABG) to avoid placing multiple stents.

Sometimes, if you prefer not to have a procedure or surgery or wouldn’t tolerate it well, your symptoms will be treated with medication alone.

IST is almost always an emergency. Up to 40 percent of people who have an IST don’t survive it. Based on the symptoms, treatment for unstable angina or a heart attack is started. Usually PCI is performed to try to reopen the artery as soon as possible and minimize heart damage.

It’s much better to prevent an IST than to try to treat it. That is why, along with a daily aspirin for life, you may receive other blood thinners, like clopidogrel (Plavix), prasugrel (Effient), or ticagrelor (Brilinta).

These blood thinners are generally taken for a minimum of one month, but usually for one year or more, after stent placement.

Current technology has made it much less likely that you’ll have restenosis from tissue overgrowth after an angioplasty or stent placement.

The gradual return of the symptoms you had before the first blockage in the artery is a sign that restenosis is happening, and you should see your doctor.

There isn’t much you can do to prevent restenosis due to excessive tissue growth during the healing process. However, you can help prevent restenosis due to underlying coronary artery disease.

Try to maintain a heart-healthy lifestyle that includes not smoking, a healthy diet, and moderate exercise. This can lower the risk of plaque buildup in your arteries.

You’re also unlikely to get IST, especially after you’ve had a stent for one month or more. Unlike ISR, however, IST is usually very serious and often causes the sudden symptoms of a heart attack.

That’s why preventing IST by taking blood thinners for as long as your doctor recommends is especially important.