In July, UW Medicine’s Regional Heart Center became the first cardiology program in Washington state to implant a dissolving coronary stent, a technological advance recently approved by the FDA.
In the United States, about 850,000 people a year are implanted with stents, narrow tube-like scaffolds that create space for normal blood flow in arteries blocked by plaque. One inescapable truth of metal stents is that they remain in the body forever; they cannot be removed and, in fact, it is not unusual for patients to accumulate many.
“Metallic stents are our bread and butter. They generally work great, but there’s room for incremental improvement,” said Dr. James McCabe, who directs the cardiac catheterization lab at UW Medical Center.
A stent designed to dissolve within three years of implant, he said, directly addresses two problems that metal stents manifest in a minority of patients.
One is scar tissue, the body’s response to a foreign object. Blood vessels normally incorporate a stent, growing around it to reform a tunnel. But overactive or unremitting growth of scar tissue can restrict or block that tunnel. Although only a small percentage of patients have such a response, the likelihood of a problem at the site of a stent grows the longer a stent is in the body.
The other problem is that a stent’s rigidity along its length reduces an artery’s ability to dilate and expand to accommodate normal changes in blood pressure. This property, vasomotion, protects smaller downstream vessels from rapid, potentially damaging changes in flow. Again, a stent’s permanence means that related problems could emerge a decade or more post-implant.
“So if we can open the blood vessel and provide that scaffolding, but then over the course of a couple years let patients return to their baseline physiologic state, conceptually that is an exciting direction,” McCabe said.
The Food and Drug Administration approved Abbott Laboratories’ “Absorb” stent for use in patients, basing its decision on results of a 2,008-person clinical trial that showed the bioabsorbable model essentially as effective and safe as a drug-coated metal stent.
The sole negative finding of that study was that the dissolving stent, in 1.5 percent of patients, was twice as likely as the conventional stent to spur clots. McCabe explained that the polymer-based Absorb stent has much thicker struts than a metal stent in order to provide similar radial strength. That additional bulk makes Absorb more problematic in arteries narrower than 2.5 millimeters.
“The results demonstrate that implantation in vessels that are borderline too small was a bad choice,” McCabe said. “We’ll be thoughtful in implementing it.”
The bigger opportunity, he suggested, lies in future iterations.
“When you compare a first-generation, basically plastic stent with a fourth-generation metal stent, the new technology has a little catching up to do before it is good for everyone. But when you think about someone whose vessels require multiple stents, having 20 stents in your body forever and having 20 stent experiences with dissolving stents are very different things.”
In the device’s first week at UW Medical Center, two patients were implanted by interventional cardiologist Creighton Don.
Bill Hagen, 79, of Seattle received two dissolving stents on July 16. Relatively fit and with no history of heart trouble, Hagen first thought his back and chest pain stemmed from his big breakfast that day, but came to the hospital as a precaution and learned he had blockages in two arteries.
“After the procedure, I felt a hundred percent better. The pain was gone. I felt ready to go home the next day,” Hagen said.
The Regional Heart Center will be the state’s exclusive provider of the Absorb stent and one of four West Coast programs with access to the technology during its early rollout,