Abbott: Absorb is comparable to drug-eluting stents

Abbott's Absorb bioresorbable stent--Courtesy of Abbott

Abbott ($ABT) released one-year data from the first randomized controlled trial of 501 patients, comparing its clinical-stage Absorb Bioresorbable Vascular Scaffold to the company's counterpart, the Xience drug-eluting stent, yesterday at the Transcatheter Cardiovascular Therapeutics conference in Washington, DC.

The Absorb didn't perform as well as the Xience on acute gain in mean lumen diameter, demonstrating a mean gain of 1.15 millimeters versus 1.46 millimeters for the Xience. However, the expert panelists at the conference didn't seem overly concerned by the result in the Absorb II trial, which they said hasn't yet translated into different clinical outcomes for patients.

"Whatever acute results you get are going to really have an affect for those first 6 to 12 months and once you have breakage of the links between the hoops, then the vessel is going to release, so if you can get through that first 6-month period you're probably okay," said panel moderator Dr. Gregg Stone of the Columbia University Medical Center. Unlike their permanent predecessors, bioresorbable stents are designed to dissolve beginning 6 months after implantation.

Reassuring was data indicating that the difference was not due to a difference in stent recoil, meaning that the stent didn't shrink greatly immediately following removal of the delivery device. Both the Absorb and Xience had a mean recoil of 0.19 millimeters, according to the study results.

The panelists attributed the difference to caution on the part of doctors when using the Absorb, especially toward the beginning of the trial, when they were unfamiliar with the Absorb's properties. The mean balloon pressure used was 14.23 atmospheres, compared to 15.03 atmospheres when implanting the Xience.

Dr. Corrado Tamburino of Ferrarotto Hospital in Italy added that the difference could be due to the fact that Absorb's polymer material is not as strong as metal.

Abbott touted adverse event data showing that patients receiving the Absorb had less chest pain (angina) than those using the Xience (16.4% compared to 25.6%). Interestingly, the study results indicate that Absorb patients also received less nitrate anti-angina medication than those on Xience. Dr. David Rizik of the Scottsdale Healthcare Heart Group concurred with Abbott, saying, "My enthusiasm for this (device) is painted by this observation very early on that we seem to notice just empirically that there was this lower rate of anginal events."

Another positive for Abbott was the low 0.6% rate of stent thrombosis, or the formation of blood clots. A previous European trial based on registry data raised concerns about the likelihood of that adverse event. Tamburino said the clinical trial rate was so low because doctors implanted the device optimally and more carefully during the randomized trial.

More details about the study are available in a paper in in The Lancet.

Abbott today announced the start of the 5-year Absorb IV clinical trial of 3,000 people, mostly in the U.S. The Absorb II trial will announce the results of its primary endpoint (vessel motion) in two years. Abbott's Absorb has already been implanted in more than 70,000 patients in Europe, where it received a CE mark in 2011. Abbott aims to secure coveted FDA approval for the device in the coming years.

- read the release
- read the release about Absorb IV
- here's the article abstract from The Lancet

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