ABSORB-3 at 2 Years: More CV Events With Absorb BVS vs Xience

Larry Hand

March 19, 2017

WASHINGTON, DC — Patients who received the Absorb (Abbott Vascular) bioresorbable vascular scaffold (BVS) in the ABSORB-3 trial showed a primary outcome, counting only events occurring between the 1-year and 2-year marks, that was noninferior to that of patients who had been stented with the same company's Xience everolimus-eluting metal stent[1].

But cumulative events in the study out to 25 months told a different story, one in which major adverse cardiac events were more prevalent with the groundbreaking Absorb stent compared with the popular Xience, as Dr Stephen G Ellis (Cleveland Clinic, OH) reported at a presentation here at the American College of Cardiology (ACC) 2017 Scientific Sessions.

By then, the rate of the target-lesion failure (TLF) primary end point—a composite of cardiac death, target-vessel MI, or ischemia-driven target lesion revascularization—came to 10.9% for the 1322 patients in the Absorb BVS group and 7.8% for the 686 who had been randomized to Xience. The end point's hazard ratio (HR) was 1.42 (95% CI 1.04–1.94) P=0.03).

Ellis pointed to a post hoc analysis of 2-year data suggesting that the increased event rate was concentrated in the patients with the smallest-caliber target vessels—that is, treated lesions with a reference vessel diameter (RVD) of <2.25 mm by quantitative angiography.

Still, the overall 2-year primary end-point difference was enough to attract the attention of the US Food and Drug Administration, which published a letter it had sent to healthcare providers, advising them of the observed increased risk of events with the BVS.

The letter on the FDA website, which says the agency is investigating the cause of the difference in events between the BVS and Xience, preceded the ACC session with Ellis's presentation. It recommends operators using the BVS follow instructions in the FDA-approved labeling for the BVS that say to avoid using it in small vessels.

The FDA letter further stated, "An additional preliminary analysis of ABSORB 3 data suggests improved clinical performance and a lower rate of complications associated with BVS implantation when healthcare providers follow the recommended implantation methods."

Ellis said in his presentation that "the trial itself was to include patients with visually assessed reference vessel diameter of 2.5 to 3.75 mm, but a full 19% of patients had a target RVD of less than 2.25 mm."

The apparent reason? Many RVDs <2.5 mm by quantitative angiography had appeared to qualify for the study when visually assessed by the operator on a standard angiogram.

Ellis was cautious when asked about the FDA letter at a press conference on ABSORB 3 that followed his formal presentation of the data. "I think the clinical community should be aware of not only the pros but the cons. I think the obstacles are surmountable. It's just a question of how much data we need. But I'll be the first to admit, we don't know for sure whether or not this device will do better over the long haul. It's one of these things in medicine where we don't have all the data," he said.

"I think the physician should have a careful and somewhat nuanced discussion with the patient before they decide what type of stent or scaffold to put in."

In an interview with heartwire from Medscape, Ellis said, "If you look at all patients enrolled in this trial, it's clear that the patients who got Xience did somewhat better. We've already identified, however, the fact that patients with small vessels shouldn't be treated with Absorb. We're beginning to accrue more and more information that proper technique benefits patients between 1 year and 2 years."

BVS noninferiority for the TLF end point vs Xience was seen at the trial's 1-year follow-up, as reported previously by heartwire .

At his formal presentation, Ellis contended that "the superiority of the Absorb BVS is not likely to emerge until the bioabsorption process is complete in approximately 3 years."

Elaborating at the press conference, he said, "The value proposition here, and I'm not saying we can prove it, is once the device goes away the outcomes will be better."

The trial had randomized 2008 patients with stable or unstable angina and up to two lesions in separate coronary arteries to receive either the Absorb BVS (n=1322) or Xience (n= 686); the mean age was about 64 in both predominantly male groups. One-year outcomes were published in 2005[2].

In the current analysis, the TLF rates came to 3.7% for Absorb and 2.5% for Xience, counting events only between year 1 and year 2; the difference wasn't significant and met noninferiority criteria.

The composite end points' individual components for Absorb BVS and Xience, respectively, came to:

  • 0.5% vs 0.4% cardiac death.

  • 1.3% vs 0.7% for target-vessel MI.

  • 2.6% vs 1.8% for ischemia-driven target-lesion revascularization.

Speaking from a panel following Ellis' formal presentation, Dr Roxana Mehran (Mount Sinai Health System, New York City) said, "We're somewhat comforted that the event rates were not extremely high. However, I think it is important for us to focus on the fact that this is breakthrough technology, and we are waiting for the promise of the future of some superiority of this device."

She added, "I think we're going to have to wait a long time after listening to this talk, given what we have seen in ABSORB 3 and overall target lesion failure."

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