One-year outcome results of the first bioresorbable coronary scaffold on the U.S. and world markets, Absorb, failed to show longer-term problems with the device that only became apparent with 3-year follow-up.
The failure of Absorb to show benefits after 3 years in the ABSORB II trial will probably not dampen enthusiasm for the concept of a bioresorbable coronary scaffold (BRS). The idea of treating coronary stenoses with a stent that disappears after a few years once it has done its job is a powerfully attractive idea, and reports from several early-stage clinical tests of new BRSs during TCT 2016 showed that many next-generation versions of these devices are in very active development.
But the regulatory hurdles these new BRSs will need to clear to prove their safety suddenly grew taller when the 3-year ABSORB II outcomes went public in a report at the Transcatheter Cardiovascular Therapeutics annual meeting and in a simultaneously published report Oct. 30.
The surprising ABSORB II results showed more than just a failure of the Absorb BRS to produce 3 years after placement the improved coronary artery vasomotion and reduced late lumen loss that were the two primary efficacy endpoints of the trial.
The results also showed troubling signs of harm from the BRS, including significantly worse late lumen loss, compared with a contemporary drug-eluting metallic stent. In addition, there was a shocking 1%/year rate of late stent thrombosis during both the second and third years following Absorb placement in coronary arteries, the period when the Absorb BRS was in the process of disappearing, and which did not occur in the study’s control patients who received a conventional, metallic drug-eluting stent.
Patrick W. Serruys, MD , lead investigator of ABSORB II, attributed these adverse outcomes to the “highly thrombogenic” proteoglycan material that formed as the Absorb BRS resorbed, and a “structural discontinuity” of the BRS as it resorbed in some patients, resulting in parts of the scaffold remnant sticking out from the coronary artery wall toward the center of the vessel.
These late flaws in the bioresorption process will now need closer scrutiny during future studies of next-generation BRSs, and will surely mean longer follow-up of pivotal trials and a shift from the 1-year follow-up data used by the Food and Drug Administration when it approved the Absorb BRS last July.
“The challenge for the field [of BRS development] is the late results, as we saw in ABSORB II,” commented David J. Cohen, MD , an interventional cardiologist at Saint Luke’s Health System in Kansas City, Mo. The ABSORB II results “will lead to reexamination of the trial design and endpoints for the next generation of BRSs,” Dr. Cohen predicted at the meeting, sponsored by the Cardiovascular Research Foundation.
The ABSORB II experience will also mean a reassessment of how long dual-antiplatelet therapy (DAPT) is needed for BRS recipients. In this trial, average DAPT duration was 1.5 years; and at 3 years, about 30% of patients in both arms of the study remained on DAPT.
“It’s not clear that BRS reduces the duration for DAPT,” Dr. Cohen noted, at least for the Absorb device, which is not full resorbed until it’s been in patients for about 3 years.
A striking property of the next-generation BRSs reported at the meeting was their use of thinner struts and faster resorption times. “These iterations hold immense promise for improving late outcomes,” commented Dean J. Kereiakes, MD , an interventional cardiologist at the Christ Hospital in Cincinnati who helped lead the large U.S. clinical trial of the Absorb BRS, ABSORB III .
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