Drug-eluting stents: Do they increase heart attack risk?

Drug-eluting stents: Do they increase heart attack risk? Learn from a Mayo Clinic doctor how to weigh the risks and benefits of stents.

Charanjit Rihal, M.D.

Recent studies have sparked a lot of questions — and confusion — about the use of popular medical devices called stents. Stents are used to keep arteries open after a procedure called angioplasty. More than 2 million people receive stents each year, including a million Americans.

For many people, angioplasty and stents have led to dramatic improvements in quality of life. However, there has been some concern about the risk that blood clots can form inside a certain type of stent known as a drug-eluting stent, leading to heart attack or death.

The Food and Drug Administration (FDA), which regulates the use of medical devices such as stents in the U.S., convened an advisory panel in December 2006 to help evaluate the use of drug-eluting stents and make recommendations on whether any changes need to be made in how drug-eluting stents are used.

Charanjit Rihal, M.D., a cardiologist and director of Mayo Clinic's Cardiac Catheterization Laboratory, Rochester, Minn., answers some questions about stents.

What's a stent?

Stents are metal mesh tubes inserted after an angioplasty into an artery that has become partially or completely blocked. Stents help prevent restenosis — when the artery becomes blocked again. Without the use of stents, about 30 percent of arteries become blocked again.

There are two basic kinds of stents: bare-metal stents and drug-eluting stents.

Bare-metal stents, as the name implies, are metal stents with no special coating. Bare-metal stents act as simple scaffolding to prop open blood vessels after they are widened with angioplasty. As the artery heals, tissue grows around the stent holding it in place. However, sometimes an overgrowth of this scar tissue in the arterial lining increases the risk that the artery will become blocked again, hence the invention of the drug-eluting stent.
Drug-eluting stents are coated with medication that is slowly released (eluted) to inhibit the growth of scar tissue in the artery lining. This helps the artery remain smooth and open, assuring good blood flow through it. Drug-eluting stents were developed because in about 20 percent of those who get bare-metal stents, tissue growth over the stent eventually leads to re-blockage. Drug-eluting stents reduce this risk to less than 10 percent, and less than 5 percent of people need repeat procedures.

Millions of people with heart problems have been successfully treated with drug-eluting stents, preventing the need for more-invasive procedures such as coronary artery bypass surgery. The reduced risk of re-narrowing from drug-eluting stents minimizes the need for repeat hospitalization and repeat angioplasty procedures — each of which carry some risk of complications including heart attack and stroke.

Why is there some concern about using drug-eluting stents?

The FDA considers both bare-metal and drug-eluting stents to be safe and effective in most people. But, all stents involve some risk. Sometimes the angioplasty procedure itself can cause complications such as a heart attack, blood clots, bleeding or injury to the blood vessels. Both bare-metal and drug-eluting stents have a risk of clotting both early and late after implantation.

It now appears that in some people who get drug-eluting stents there's a small increased risk of blood clots forming in the stent once the drug coating has been used up — sometimes a year or more after stent implantation. This risk is still quite low; about 0.5 percent or less when stents are used for FDA-approved reasons. The risk appears to be slightly higher when drug-eluting stents are used for off-label uses, ranging from about 0.4 percent to 1.6 percent.

So what does the FDA say?

An FDA advisory panel found that when drug-eluting stents are used "on-label" — meaning for specific situations approved by the FDA — there was no increased risk of heart attack or death with drug-eluting stents compared with bare-metal stents. However, about 60 percent of the time stents are used for "off-label" indications — meaning for reasons which while appropriate are not specifically spelled out in the FDA guidelines. When stents are used off-label, it's generally for more-complex cases, such as in someone who has multiple blockages and other complications.

The FDA panel said when drug-eluting stents are used off-label there's a small but increased risk of blood clotting that can lead to heart attack and death. But, it's unknown if drug-eluting stents cause this increased risk or whether people in this group tend to be at higher risk in the first place.

There are a variety of potential explanations for blood clots developing later after implantation. Much of it may have to do with how long a person takes anti-platelet medications — aspirin, clopidogrel (Plavix) — which help prevent blood clots from forming in the stents. If these medications are stopped earlier than recommended or an individual doesn't have an effective response to the anti-clotting medications, there can be problems. People also have varying healing times.

Could you further explain on-label vs. off-label use?

Before a device is approved, the FDA must be satisfied it's safe and effective when used as the manufacturer intends. Using a device according to its guidelines is called on-label use because a device is used according to directions on the label. However, it's common for doctors to use devices, as well as drugs, off-label. There's nothing inherently wrong with that. Frequently, doctors discover that a device or drug can be beneficial in more instances than just those the FDA evaluated when it was first developed.

For example, in the case of drug-eluting stents, scientific studies now show their benefits in the treatment of people with acute heart attacks, but this is not included in the original "label." Thus, while the FDA has approved drug-eluting stents for specific reasons, there are a variety of situations in which doctors must use their clinical judgment to determine case by case whether a drug-eluting stent is appropriate for any given individual.

So, bottom line, are drug-eluting stents safe or not?

Based on all presently available information, drug-eluting stents are safe and effective in most circumstances. The key is you must be willing to take your medications in the prescribed manner and for the prescribed duration to help ensure safety.

The FDA advisory panel said it's difficult to know for certain what the long-term risks of using drug-eluting stents might be because there's simply not enough information at the current time. However, the panel said the benefits of drug-eluting stents outweigh concerns about blood clot formation when drug-eluting stents are used on-label according to the manufacturer's directions. The panel said when drug-eluting stents are used off-label, it's unclear how much risk people might face. The panel recommended more study in this area.

It's important to remember that in all circumstances studied so far, drug-eluting stents have been shown to be more effective than are bare-metal stents, with less risk of restenosis and the associated risk of more procedures.

It's worth reminding people that you basically have four options if your arteries become narrowed, each with risks:

Bare-metal stents. These stents can work well, but have a much higher rate of restenosis than drug-eluting stents. If you will need some type of noncardiac surgery soon (for example, a stomach or hernia operation), you may do better with a bare-metal stent.
Drug-eluting stents. As we've been discussing, these stents work well and have a lower rate of restenosis than bare-metal stents. The issue we're trying to sort out now is whether the use of drug-eluting stents in some people causes a higher risk of dangerous blood clots. As of right now, we can't give a definitive answer.
Coronary bypass surgery. Bypass surgery is used to divert blood around blocked arteries in the heart. This surgery uses a healthy blood vessel harvested from your leg, arm, chest or abdomen and connects it to the other arteries in your heart so that blood is bypassed around the diseased or blocked area. While bypass surgery does work well, it's also more invasive than using stents, which means a longer recovery time. In addition, the risk of complications for bypass surgery can be higher than with stents.
Medications and lifestyle changes. This is a good option for many people. If you have symptoms from your narrowed arteries, such as angina, and your condition isn't severe or immediately life-threatening, it may be worth first trying medications such as statins and lifestyle changes such as eating a more balanced diet. In fact, a recent medical study called the COURAGE trial, found medications and lifestyle changes worked as well as stents in people who were able to stay on their medications as directed. Keep in mind that even if you receive a stent, your doctor will likely also prescribe medications such as statins.

What should you do if you have a drug-eluting stent?

It's very important that you take anti-clotting medications exactly as directed by your doctor. Here's what to do if you have a stent of any kind:

Take aspirin. If you have a stent, you'll have to take aspirin daily and indefinitely to reduce the risk of clotting.
Take anti-clotting medication. People with stents are given prescription anti-clotting medications such as clopidogrel (Plavix). The American Heart Association and FDA recommend that people who have had drug-eluting stents inserted should continue to take medications such as Plavix to reduce the risk of blood clots for at least one year after the stent is inserted.
Listen to your cardiologist. Always talk with your cardiologist about how long you should take anti-clotting and other medications because the answer will vary depending on the nature of the blockage you had and your risk of bleeding. The most important thing to remember is to take all your medications in the manner your doctor prescribes.

If you're considering noncardiac surgery (meaning, not related to your heart) in the year after receiving your stent, there are some additional things to keep in mind:

If possible, you should postpone your noncardiac surgery for one year after receiving a stent.
If the surgery can't be postponed, discuss with your doctor medications you should be taking at the same time, such as aspirin or clopidogrel. Your medication dosages might need to be changed.

What if you need a stent? Should you get a bare-metal stent instead of a drug-eluting stent?

Generally, no. The most important thing to do is have a conversation with your doctor about the risks and benefits. Keep in mind that compared with a bare-metal stent, a drug-eluting stent dramatically reduce the chances your artery will become clogged again.

However, if you're likely to need surgery in the year after you get a stent, are at an increased risk of bleeding or don't think you'll be able to take anti-clotting medications as prescribed by your doctor, a bare metal stent — or another treatment — might be a better choice. Again, talk with your doctor about your situation.