Invisible repair: Optical coherence tomography shows an artery immediately, six months, and two years after a stent is put in place. At six months, a small amount of tissue has created a bridge between two of the stent’s ribs; after two years, the bridge and the struts have largely disappeared.
“Phase A of the project was really a proof of concept, but I think the concept was very successful” says Stone, who is on Abbott’s BVS advisory board. “Why have a permanent, metallic prosthesis if you don’t have to?”
“I think it’s a wonderful concept,” says Frederic Resnic, the director of the Cardiac Catheterization Laboratory at Brigham and Women’s Hospital in Boston. “But the bar to prove that it is more than just a niche product is going to be very high, because you’re going to have to meet or exceed the results of 2009 drug-eluting stents, and it’s very hard to demonstrate that level of safety and efficacy.”
Abbott is not quite there yet. For a second trial, launching now, the company is using a slightly modified version of the earlier stent; it is easier to store (the first had to be kept at -20 degrees Celsius to prevent the polymer from cracking) and has slightly thicker, stronger struts to help maintain the arterial opening and better prevent re-narrowing. This trial will still be limited to patients with simple lesions and will be only slightly larger than the first, with planned enrollment of 80 people in Europe, Australia, and New Zealand.
Because metal stents have proven to be so effective, some question whether a bioabsorbable version is worth the research investment, especially since the bar to prove both safety and efficacy is set so high, and since there’s not yet proof that the disappearing stent doesn’t leave scarred tissue in its wake. But Ormiston and Stone point to the fact that their patients’ arteries appear to have restored elasticity and that eroding stents don’t prevent the branching-off of new vessels, unlike the metal ones. Plus, they note that patients often have to return for a second stent placement–if the first stent has been absorbed, it can’t get in the way of a second surgery.
These are all distant possibilities, however, and will remain so until patients with more-complex conditions have been treated successfully. “The current study is far from definitive from a clinical perspective,” Resnic says. “Large prospective clinical trials will be necessary to demonstrate that this bioabsorbable platform is as safe and effective as existing [and future iterations of] commercially available drug-eluting stents.” But, he adds: “if perfected, I believe it would naturally replace permanent metallic implants.”