Drug eluting stents (DES) – wire mesh tubes that prop open a previously blocked artery to the heart – have gone a long way toward reducing restenosis in cardiac patients after percutaneous coronary intervention. But they’ve also created a host of potential complications from impairing imaging to hindering surgical revascularization or positive remodeling (an increase in arterial area).

A new bioabsorbable stent being tested by Abbott Laboratories (Abbott Park, Illinois) may solve some of those problems. One-year results from a study of 30 patients who have had bioabsorbable everolimus eluting stents implanted demonstrated no stent thrombosis, no clinically driven target lesion revascularizations (retreatment of a diseased lesion), and a low (3.3%) rate of major adverse cardiac events (MACE).

“Doctor’s tell me their patients often ask, ‘How long do I have to have this stent inside me?’” Richard Rapoza, PhD, VP of research and development for the bioabsorbable stent program at Abbott told Medical Device Daily. “They don’t understand or like the idea that they are permanent. For patients who have angioplasty, their vessels regrow in one to five years, but if you have a metallic stent, that’s not a possibility. Now we are able to restore that possibility, we have a stent that degrades.”

Abbott said theirs is the first degradable stent to ever be tested in humans.

The bioabsorbable stent has a backbone of poly-L-lactic acid that provides the support and a coating of poly-D,L-lactic acid that contains and controls the release of the antiproliferative agent everolimus. Polylactic acid is a substance commonly used in medical implants such as dissolvable sutures. The substance reacts to water and is absorbed by the body over time.

Patients included in the trial had either stable, unstable, or silent ischemia and a single lesion that was suitable for treatment with a single 3.0 12 mm or 3.0 18 mm stent. Rapoza pointed out they were 60-70 years old and did not have complicated disease and no calcifications.

They were enrolled from four academic hospitals in Auckland, New Zealand, Rotterdam, the Netherlands, Krakow, Poland, and Skejby, Denmark. The composite endpoint was cardiac death, myocardial infarction and ischemia-driven target lesion revascularization. Researchers are checking patients at 30, 180 and 270 days, with an annual follow-up for up to five years, on blood clot formation rates.

No late stent thromboses were recorded. At 6-month follow-up, the angiographic in-stent late loss was 0.44 mm and was mainly due to a mild reduction of the stent area.

Abbott’s stent loses mechanical structure in three to five months and the vessel can begin to move freely. “It holds an artery open long enough for healing to occur,“ Rapoza said. Remnants of the structure can remain up to two years after implantation. “We would expect an artery that is healed to function as it did before it became diseased.”

Rapoza said one of the more interesting aspects of the study is to follow patients over the course of five years to see if their vessels can actually regrow. “We’re looking to see if the theory that the vessel can re-grow post-one year is real,” he said.

Another potential advantage of a stent that degrades is that patients can then discontinue antiplatelet therapy. Thienopyridines and aspirin, antiplatelet agents, are begun before stent insertion to reduce the chance of clotting within the stent, which may result in heart attack or death. But patients often prematurely stop taking the drugs.

“Complications related to DES are often related to patient compliance. If this stent is gone, patients won’t need to continue antiplatelet therapy in the long term,” Rapoza said. “The medications are expensive and older people have a problem complying with long term use of the drugs. Plus, when patients have other health problems, they have to stop the antiplatelet medications and then there are more problems.”

The ABSORB trial is a prospective, non-randomized (open label) study designed to enroll up to 60 patients.

“We stopped enrolling at 30 patients because we wanted to see the results before adding the other 30 patients. We made some adjustments to the structure of the stent, changed the pattern to improve scaffolding and improved the degradation rate,” Rapoza said.

“The positive results from this clinical trial form a strong basis for the development of additional bioabsorbable stent platforms with the potential to eliminate some of the restrictions posed by metallic stents in areas such as vessel imaging and vessel remodeling,” said Patrick Serruys, MD, PhD, professor of interventional cardiology at the Thoraxcentre, Erasmus University Hospital (Rotterdam, the Netherlands) and co-principal investigator in the ABSORB study.

Rapoza said plans are in the works to launch a larger study in Europe, although Abbott has yet to release those details.