Stents are small expandable tubes used to treat narrowed or weakened arteries in the body. In patients with coronary heart disease, caused by the buildup of plaque, stents are used to open narrowed arteries and help reduce symptoms such as chest pain (angina) or to help treat a heart attack.
These types of stents are commonly called heart stents, but they're also referred to as cardiac stents or coronary stents. Usually made of metal mesh, heart stents are implanted in narrowed coronary arteries during a procedure called a percutaneous coronary intervention (PCI) or angioplasty.
Unlike coronary artery bypass surgery, stenting is considered minimally invasive because it involves no major incisions. Performed with local anesthesia and mild sedation, the procedure usually takes about an hour, but it can take longer if multiple stents are required. Patients who undergo stenting experience significantly less discomfort and a shorter recovery time than those who undergo coronary artery bypass surgery.
But stenting isn't risk-free. Sometimes, a blood clot can form in the stent and cause a sudden renarrowing or even a complete blockage. To prevent this process, which is known as in-stent thrombosis, patients who undergo stenting must take one or more blood-thinning drugs after the procedure. These include aspirin, which usually must be taken indefinitely, and Brilinta or clopidogrel (Plavix), which is usually prescribed for at least one and up to 12 months.
Any manipulation of an artery (whether with a balloon or stent) can result in some injury to the blood vessel wall, especially the endothelium (the innermost layer of a coronary artery). So scar tissue can also form within the stented area, resulting in renarrowing over a period of months. This process is called restenosis. If restenosis develops, another stent procedure can often be used to solve the problem. In some patients whose stented arteries reclose, coronary artery bypass surgery may be necessary.
Types of Heart Stents
In the late 1970s, doctors began using balloon angioplasty to treat narrowed coronary arteries. During this procedure, a very thin, long, balloon-tipped tube, called a catheter, is inserted into an artery in either the groin or arm and is moved to the site of the blockage with help from an X-ray. The balloon at the tip of the catheter is then inflated to compress the blockage and restore blood flow, and then it’s deflated to allow the catheter and balloon to be removed.
Because no new support is left at the site of the blockage during balloon angioplasty, in a small percentage of cases, the artery will resume its previous shape or even collapse after the balloon is deflated. In addition, about 30% of all coronary arteries treated with balloon angioplasty are affected by restenosis.
To help solve these problems, doctors developed small stents which could be mounted on the balloon section of the catheter and inserted into a blood vessel. During a stenting procedure, the stent expands when the balloon is inflated, locks into place, and forms a permanent scaffold to hold the coronary artery open even after the balloon is deflated and removed.
In 1986, French researchers implanted the first stent into a human coronary artery. In 1994, the FDA approved the first heart stent for use in the U.S.
First-generation stents were made of bare metal. Although bare-metal stents almost eliminated the risk of the artery collapsing, they only modestly reduced the risk of restenosis. About 25% of all coronary arteries treated with bare-metal stents would close up again, usually within about six months.
So doctors and companies began testing stents which were coated with drugs that interrupted the process of restenosis. These are called drug-eluting stents, which are now approved by the FDA.
In clinical trials, drug-eluting stents dramatically reduced the rate of restenosis to less than 10%. Drug-eluting stents also reduced the need for repeat procedures in patients with diabetes, a condition associated with an increased risk of restenosis.
Despite these benefits, there were concerns that drug-eluting stents were associated with a rare but serious complication: late in-stent thrombosis, in which a blood clot forms inside the stent one or more years after it's implanted. Because this complication can be fatal, it is extremely important that patients with drug-eluting stents take aspirin and an anticlotting drug such as Plavix, Effient (prasugrel), orTiclid (ticlopidine) as prescribed, and not stop them without their doctor's approval.
Innovations in Heart Stents
Due to concerns such as late in-stent thrombosis, the use of drug-eluting stents started to decline in late 2006. But many cardiologists believed that fears were overblown. They also began to re-examine whether drug-eluting stents were significantly more effective than the older bare-metal stents, especially in patients with blockages that were deemed to have a low risk of restenosis.
In December 2006, the FDA held a public meeting on the issue of late in-stent thrombosis. While concluding that more information was needed, the agency stated that drug-eluting stents, when used as directed, were not associated with an increased risk of heart attack or death. Subsequent research studies confirmed the safety and effectiveness of drug-eluting stents, prompting the continued development of new stent technologies.
In recent years, the usage of drug-eluting stents has steadily increased, and the global market for heart stents is expected to exceed $8 billion by the year 2015.
Many new second- and third-generation stent designs are under development, in clinical trials, or have been approved for use outside the U.S. These include:
- A stent with a covering that delivers an anti-restenosis drug over a period of several months and then essentially becomes a bare-metal stent
- A stent that is absorbed by the body and disappears after it has done its work
- A stent which uses a bio-engineered coating to quickly create a thin, all-natural layer inside the artery
Other technologies under development include platinum-coated stainless steel stents, diamond carbon-coated stents, and gene therapy/antibody-coated stents.