A coronary stent is a small tube made of metal or plastic. Stents were introduced to help solve the problem of rebound blockage following balloon angioplasty, whereby compressed atherosclerotic deposits re-expand into the artery, reversing the effects of the procedure. During angioplasty surgery, the stent is implanted along with a balloon that expands the area of arterial blockage, according to the American Heart Association. The balloon is inflated to open the blockage, and then the stent is put in place while the balloon is deflated and removed.
Metal
Metal stents, also known as bare metal stents, are made of stainless steel or a cobalt-chromium alloy, and have been used in the United States since 1994. Complications involve immune reactions to the metal that lead to scar tissue formation around the stent, creating a secondary form of occlusion. The area of the stent is also prone to clot formation, and after placement of a bare metal stent patients must take antiplatelet medication and aspirin on a permanent basis. In spite of this postoperative therapy, bare metal stents can become blocked--a condition known as restenosis--in about 25 percent of cases, necessitating repeat surgery. Restenosis is categorized according when it occurs after surgery. Early restenosis occurs within 30 days; 30 days to a year is considered late stenosis; and beyond a year is referred to as very late, according to a 2009 article in the "Journal of Invasive Cardiology." Medical News Today reports that bare metal stents have been found to be superior to other types in cases where another, unrelated surgery is performed within a few weeks after receiving a stent.
Drug-eluting
Drug-eluting stents are made of metal coated with a polymer material that contains a drug that is slowly released over time to prevent post-stent clot formation. In 2006, 74 percent of stents implanted were drug-eluting, says the American Heart Association. The January 2009 issue of the "New England Journal of Medicine" reported that in cases of acute myocardial infarction, or heart attack, drug-eluting stents are associated with a decreased mortality as well as decreased incidence of restenosis requiring surgery within 2 years of stent placement. Drug-eluting stents become blocked due to restenosis in 7 percent of cases, according to the website Stent Plus. Researchers in Denmark who studied nearly 12,400 stent patients concluded that there was a statistically significant increase in thrombosis and heart attacks in the drug-eluting stent group as compared to those with bare metal stents in the 12- to 15-month time frame following surgery.
Plastic
A plastic stent has been developed as an alternative to metal or drug-eluting stents. This stent, made of a lactic acid polymer, has the advantage of dissolving completely after about 18 to 24 months. While the stent is in place, it props open the artery, which heals and strengthens during that time, so that by the time the stent is absorbed by the body, the healed artery is ready to take over its job, unassisted. The designer of the plastic stent, Hideo Tamai, says that stents are really only needed for six months because of the natural healing process that takes place.
References
- Invasive Cardiology: Very Late Stent Thrombosis after Bare-Metal Stent Implantation: Case Reports and Review of the Literature
- Medical News Today: Bare-Metal Stents Are Better For Some Heart Patients
- American Heart Association: Stent facts
- National Center for Biotechnology Information:Drug-eluting or bare-metal stents for acute myocardial infarction.
- Stent Plus: Bare-Metal vs. Drug-Coated Stents
