You are here:

Building a better stent

Wire tubes that prop open arteries continue to be refined.

Small metal cylinders called stents have helped revolutionize the treatment of heart disease. In an angioplasty procedure, a narrowed or blocked artery is opened with a balloon. A stent is then inserted to hold the artery open—all without the trauma of open-heart surgery.

Despite the success of stenting—more than 500,000 stents are implanted every year—the devices aren’t perfect. “There is no question that angioplasty with stents saves lives in certain cases, such as in people who are having a heart attack. However, we are still looking for the formula that, over the long run, will also guarantee that the artery will not become narrowed again by growing through the stent or attracting blood clots. Stents are moving closer to that ideal,” says Dr. Deepak L. Bhatt, chief of cardiology at the Harvard-affiliated VA Boston Healthcare System, “but the protection is not perfect yet.”

New stent designs

Today’s stents expand to a preset size that is the same throughout the length of the stent. Stents are selected for an individual based on the estimated interior diameter of the artery being treated. When an artery has an irregular shape, or a spasm prevents the artery from being accurately measured, the chosen stent may not fit tightly against the artery wall. The French company Stentys has created a stent that expands by itself to fit the shape and diameter of an irregular artery wall. After it is implanted, the Self-Apposing stent continues to change shape as the artery swells and flexes.

Photo courtesy of Stentys.

Self Apposing Stent

Self-Apposing stent

When a stent is deployed inside an artery that has been blocked by a clot, there is a risk that a bit of clot will break off and be carried in the blood to another location, where it can threaten life or limb. To reduce the likelihood this will happen, InspireMD has covered its MGuard stent with a fine mesh knit from a single fiber.

MGuard stent

MGuard stent

An evolving concept

The first stents were made of bare metal. They proved strong enough to hold arteries open, but they sometimes became clogged when cells in the artery wall multiplied and grew through the holes in the stent, blocking the flow of blood through the artery. This process is known as restenosis. Restenosis often required the individual to undergo another angioplasty or have bypass surgery to route blood around the blockage. (Doctors call the restoration of blood flow with either angioplasty or bypass surgery “revascularization.”)

Coating the stent with a drug that gradually seeps (elutes) into the surrounding tissue reduced the problem of restenosis inside the stent. However, the first “drug-eluting” (coated) stents tended to promote the formation of blood clots that could suddenly block blood flow and cause a fatal heart attack. Although this happened rarely, it required the person to take two drugs that inhibit blood clotting (aspirin and clopidogrel) for at least one year after the stent procedure.

In recent years, using different drugs to coat the stent has produced better results. “These drug-eluting stents have low rates of clogging up and very low rates of clotting. They seem to be better than the first drug-eluting stents, as well as bare-metal stents,” says Dr. Bhatt.

These qualities have translated into lower rates of heart attack and less need for later bypass surgery.

Although some drug-eluting stents have been shown to do a better job than others, all drug-eluting stents are better than bare-metal stents at preventing in-stent clogging and the need for revascularization. Yet there is room for improvement.

Looking ahead

Efforts to perfect drug-eluting stents are progressing on multiple fronts:

  • coating a stent with two drugs (several combinations are being tested)

  • coating the stent with a drug that has never been used in stents before (the BioMatrix Flex and BioFreedom stents by Biosensors)

  • covering the stent with mesh to prevent bits of plaque or overgrown restenosis tissue from breaking away and being carried by the bloodstream to another location (the MGuard Embolic Protection Stent by Inspire MD)

  • allowing the stent to expand by itself to fit snugly inside an artery of any size (the Self-Apposing stent by Stentys)

  • creating a stent that is absorbed by the body after its drug coating has been used up (the MiStent by Micell Technologies).

These innovative stents have yet to be studied in enough people to know how effectively they prevent repeat blockages.

“In the future, we are likely to see stents that are less likely to clot, even when an individual does not take anti-clotting medications,” says Dr. Bhatt. “We are also likely to see stents that have even lower rates of restenosis than the current low rates.”

Posted by: Dr.Health

Back to Top