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While the Absorb bioresorbable vascular scaffold had target vessel failure rates similar to conventional metallic stents in an all-comers trial, it yet again highlighted the risk of device thrombosis.

Over 2 years, target vessel failure occurred at comparable rates between Absorb scaffolds and Xience everolimus-eluting stents (11.7% versus 10.7%, HR 1.12, 95% CI 0.85-1.48) in the Amsterdam Investigator-Initiated Absorb Strategy All-Comers (AIDA) Trial. Individual components of the primary endpoint were not significantly different, either:

• Cardiac death: 2.0% versus 2.7%
• Target vessel MI: 5.5% versus 3.2%
• Target vessel revascularization: 8.7% versus 7.5%

The main difference lay in device thrombosis rates (3.5% versus 0.9%, HR 3.87, 95% CI 1.78-8.42), Joanna J. Wykrzykowska, MD, PhD, of the Academic Medical Center-University of Amsterdam, and collaborators reported in the .

Ten patients developed scaffold thrombosis more than a year after Absorb placement -- of those, one had the problem arise more than 2 years out.

Published data were from a preliminary analysis: the data and safety monitoring board had gotten wind of the elevated risk of scaffold thrombosis in other studies and recommended early reporting of the results due to the safety concern. All patients had been enrolled with follow-up incomplete (a median of 707 days).

The ABSORB series of trials had raised concerns over target lesion failure and stent thrombosis, which were not alleviated by recent presentation of 2-year data from the pivotal ABSORB III trial. Instead, the FDA announced that it is investigating the device's safety.

While proponents have pointed to technique as key to outcomes, AIDA showed rates of predilatation and postdilation, along with implanted vessel size, were similar between patients whose scaffolds developed device thrombosis and their peers whose devices didn't.

"An observational study showed that the 1-year rate of scaffold thrombosis was lower when a scaffold-specific implantation strategy (consisting of predilation, adequate sizing, and postdilation) was used. In our trial, scaffold thrombosis occurred regardless of implantation technique," Wykrzykowska's group commented.

The AIDA investigators are also now giving extended dual antiplatelet therapy (DAPT) to Absorb recipients.

Debabrata Mukherjee, MD, of the Texas Tech University Health Sciences Center in El Paso, questioned whether a longer duration of DAPT would truly offset the risk of scaffold thrombosis. Nevertheless, "prolonged DAPT is likely to be recommended and indeed was recommended by the data and safety monitoring board overseeing AIDA."

"Therefore, the bioresorbable scaffold should be used only in patients who can adhere to DAPT for an extended period, possibly up to 3 years, without unacceptable side effects. The extended duration of DAPT will come at the cost of a higher risk of bleeding, which will further attenuate any potential longer-term benefits of currently available bioresorbable scaffolds," he wrote in an accompanying editorial.

"Given the lack of putative benefit in the ABSORB Japan and ABSORB II trials, the advantage of bioresorbable technology over metallic stents remains to be established," Wykrzykowska and colleagues agreed.

The investigators found that scaffold implantation took 5 extra minutes of procedure time and required 9 mL more contrast material. There was also a lower likelihood of receiving the assigned device than with Xience implantation. "These findings attest to delivery challenges associated with scaffold implantation," they commented.

The AIDA trial had 1,845 patients randomly assigned to undergo PCI with the Absorb scaffold (n=924) or the Xience stent (n=921). Five high-volume Dutch centers participated in the trial.

As for its limitations, routine intravascular imaging was not performed during implantation, there was no systematic blood sampling done, and not all case-report forms were monitored.

"The AIDA investigators should be congratulated for highlighting an important safety issue," Mukherjee maintained.

"The current study extends the concern regarding bioresorbable scaffold thrombosis to a broader population of patients. Given the lack of an advantage with respect to clinical efficacy, the challenges in delivering the device (including longer procedural times), and the higher rate of device thrombosis with the bioresorbable scaffold, there is little justification for routine use of the everolimus-eluting bioresorbable scaffold over the everolimus-eluting metallic stent."