Minneapolis Heart Institute part of trial for dissolving stent

Last week, Dr. Nicholas Burke of the Minneapolis Heart Institute Foundation implanted a stent into the coronary artery of a patient to help hold open a previously blocked blood vessel. Nothing super extraordinary there — cardiologists have been using tiny metal stents for a decade.

The difference is that the stent wasn't made of metal and, in about two years, it will have dissolved and disappeared.

Burke is one of the first cardiologists — and the heart institute at Abbott Northwestern Hospital is among the first centers — in the country to implant Absorb, a drug-coated stent that the body absorbs, as part of the Absorb III trial. The trial will enroll 2,250 people, mostly in the United States, to evaluate the safety and effectiveness of the new stent made by Abbott Laboratories, an Illinois-company.

"This could be transformational. It could really change how things are done," Burke said. "It's big."

Perhaps the biggest advantage to a disappearing stent, physicians say, is that it leaves no metal behind. While stents act as scaffolding, helping an artery to heal, there is some thought that leaving a piece of metal in the artery could have negative consequences. It may encourage new plaque to re-form over time, said Dr. Richard Schwartz, another MHIF cardiologist. Or it could contribute to the formation of a potentially dangerous blood clot.

"It's quite rare, but it's a concern," he said.

Another issue with metal stents, Schwartz said, is the "full metal jacket" effect. This occurs when a patient needs multiple stents over time. An artery filled with the tiny metal tubes can make a future coronary bypass more difficult.

However, there are potential disadvantages to the Absorb stent, Schwartz said. Because it is made from a polymer and not metal, it is more fragile. Because of that, its mesh is thicker and less flexible than a metal stent and it cannot fit into the tiniest of blood vessels and it cannot be "stretched" to fit better during implantation.

"It's bigger and clunkier," he said. "Like driving a dump truck instead of a sports car."

Still, he said, it's an encouraging option. In part, because after the stent has dissolved, the blood vessel can regain its natural ability to flex and stretch as the body needs more blood — something that metal stents do not allow.

The stent business, while shrinking recently as physicians face scrutiny over using stents too often, still is worth about $2 billion annually in the U.S. and has a total worldwide market of about $3.5 billion. Medtronic and Boston Scientific are major players in a very competitive marketplace. However, said Danielle Antalffy, an analyst with Leerink Swann Research, Abbott is "way ahead" in the area of developing a disappearing stent. That advantage could leave it poised to gain major market share if Absorb proves successful, she added.

"This would definitely be the biggest innovation we've seen," she said, similar to when companies found a way to coat stents with drugs to be more effective in keeping arteries open. "But, if it were to become a big deal, it would be about five years from now."

Since the 1970s, physicians have treated patients with coronary artery disease with balloon angioplasty, followed by placing a metal stent, and now a drug-coated metal stent, to keep the artery open over time. Abbott began developing Absorb about a decade ago. It launched the device in India in December. Absorb is currently available in more than 30 countries across Europe, Asia and Latin America.

Abbott said the main endpoint of the trial is to keep the targeted spot in the artery clear of plaque, as well as safety to the patient, at one year. Burke said its real effectiveness will be measured over several years.