Researchers at the Cleveland Clinic have been at the forefront of investigations into a promising new update to stent technology — the bioresorbable vascular scaffold.
Stephen G. Ellis, MD, director of interventional cardiology and senior academic officer for cardiology at Cleveland Clinic and co-primary investigator for the ABSORB III trial, told Cardiology Today’s Intervention. “Every year, 2% to 3% of patients have an adverse event related to the stent, and that risk seems to go on indefinitely as best we can tell. So, for the average 60-year-old — and that’s about the average age of people who receive stents — if they’re going to live another 20 years, there is a 50/50 chance they are going to have a bad outcome related to that stent over their lifetime.”
Stephen G. Ellis
Ellis spoke with Cardiology Today’s Intervention about this ongoing risk for adverse events, the use of bioresorbable scaffolds to mitigate this risk and current research on these devices.
Question: What is the cause of adverse outcomes related to stent implantation?
Answer: Quite honestly, we don’t fully understand why this happens, but we think that the presence of the stent likely causes inflammation leading to neoatherosclerosis (rapidly developing atherosclerosis within the stent), and it may cause entrapment or “jailing” of the vessel. In a normal vessel, if it develops new plaque, it will expand to try and compensate, but a stented vessel can’t do that because it is trapped.
Question: How might a bioresorbable scaffold be different?
Answer: The idea is, if you can make a plastic biorebsorbable stent, it would have the same early benefits, and then go away. It certainly wouldn’t entrap the vessel, and maybe there would be less inflammation in the tissue.
The next thing to understand is that because plastic is not as strong as metal, the actual struts of these devices have to be thicker than the current metallic stents. Otherwise, they wouldn’t support the vessel.
Question: What did the ABSORB III trial investigate?
Answer: The ABSORB III trial was the U.S. pivotal trial of the Absorb everolimus-eluting bioresorbable vascular scaffold (Abbott Vascular). It was a large multicenter trial. We randomly assigned 2,008 patients with stable or unstable angina, in a 2:1 ratio, to receive the Absorb BVS (n = 1,322) or the Xience everolimus-eluting stent (Abbott Vascular; n = 686). It’s important to understand that the Xience DES is the best DES available in the United States right now. We followed these patients for 1 year and presented the outcomes.
At 1 year, the primary outcome of target lesion failure occurred in 7.8% of patients who received Absorb BVS vs. 6.1% of patients who received Xience (difference, 1.7 percentage points; 95% CI, –0.5 to 3.9). While Xience trended toward doing better, the 95% confidence limits did not cross the 4.5% difference that was established with the FDA as the definition of noninferiority. This percent difference was diminished further in an analysis that excluded patients who should not have been eligible. Eighteen percent of patients in the Absorb BVS group and 19% in the Xience group should not have been enrolled because their vessels were smaller than the 2.5-mm to 3.75-mm diameter that was part of the inclusion criteria for the study. These patients did considerably worse. The results were reasonably comparable among patients who were actually intended to get into the study, as long as the operators used meticulous techniques to properly size and embed the scaffold onto the vessel wall.
In addition, many, if not most, operators in the study were putting the scaffold in for the first time, whereas they had used Xience for years, so perhaps the Absorb group was disadvantaged in this regard.
Question: How close is widespread use of the bioresorbable vascular scaffold?
Answer: The Absorb BVS is currently available in about 70 countries worldwide. It is not yet available in the United States. This is a first-generation plastic-dissolving device. There are second-generation devices that are in early phase clinical trials with thinner struts. We simply have to await the long-term results. – by Jennifer Byrne
Disclosure: Ellis reports paid consulting for Abbott Vascular, Boston Scientific and Medtronic.