Coronary stents have revolutionized the treatment of heart disease, but they leave metal scaffolding inside arteries that can occasionally cause immune reactions and blood clots, and interfere with future surgeries. A new, fully absorbable stent could one day help prevent problems like these. The stent, made by Abbott Laboratories in Illinois, just finished its first test--a two-year trial involving 30 patients--and now, after a few adjustments, the company is launching its next phase of clinical tests.

Surgeons use stents to open blocked arteries, but the devices can cause complications. The materials used incite an immune response, and damage to the artery wall can trigger the formation of blood clots that, once dislodged, can cause stroke or other damage in a process called late stent thrombosis. Over the past few years, these complications have decreased with the widespread use of anticlotting therapies and drug eluting stents coated with immune suppressants. But some cardiologists still liken the use of metal stents to leaving a cast in place once a person's broken limb has healed.

Abbott's new bioabsorbable everolimus-eluting stent, or BVS, is made up of two layers of a biodegradable polymer: one that contains the immunosuppressant drug everolimus, the other forming a longer-lasting backbone. Over time, the body breaks down and absorbs the polymer, ultimately leaving nothing behind. For its initial test run, the stent was placed in patients with just a single narrowed or blocked artery. According to research published this month in The Lancet, the stent appeared to be almost completely absorbed after two years, with no instances of cardiac death, no known cases of stent thrombosis, and no evidence that the arteries had begun to re-narrow.

"It really looks like the stent did its job of stopping re-narrowing, it was safe, and it disappeared," says John Ormiston, lead researcher of the Lancet study and an interventional cardiologist at Mercy and Auckland City Hospitals in New Zealand. "We have hope that the long-term chance of thrombosis will be very low."

Because the stent was tested on so few people, however, and because those patients had very simple problems, it is difficult to know whether it will match the long-term success of its metal predecessors. "It certainly appears to work in patients with simple lesions, but it won't get widespread use unless it works in more-complex patients," Ormiston says.

"If you have a stent that's bioabsorbable, could return a vessel to its native condition and protect it from late-stent thrombosis, that's an inherently appealing concept, especially when you talk about the fact that we're implanting about a million patients per year here in the U.S.," says Gregg Stone, director of cardiovascular research and education at New York-Presbyterian Hospital and the Columbia University Medical Center.