Negative Data Piling Up on Absorb Bioresorbable Scaffold

Patrice Wendling

April 03, 2017

AMSTERDAM, NL — Consistent with prior trials, the risk of scaffold thrombosis was significantly higher in patients receiving the Absorb (Abbott Vascular) bioresorbable vascular scaffold (BVS) than an everolimus-eluting metallic stent (Xience, Abbott Vascular), according to 2-year data from the Amsterdam Investigator-Initiated Absorb Strategy All-Comers Trial (AIDA)[1].

There was no significant difference in the risk of target vessel failure (TVF) or target lesion failure, as was observed in the 2-year data just reported from ABSORB 3 at the American College of Cardiology 2017 Scientific Sessions.

AIDA's primary end point of TVF occurred in 11.7% of patients treated with Absorb and 10.7% of patients treated with Xience (P=0.43) at 2 years.

Rates were similar between the two groups for cardiac death (2% vs 2.7%) and target vessel revascularization (8.7% vs 7.5%), but this was offset by a significantly higher rate of target vessel MI for Absorb BVS (5.5% vs 3.2%; P=0.04).

Speaking to heartwire from Medscape, lead author Dr Joanna Wykrzykowska (Academic Medical Center, Amsterdam, the Netherlands) said the TVF results "speak to the fact we did a pretty good job of treating our patients," but there remains a safety issue that limits the ability to use the Absorb BVS.

"Even for simple lesions, although the risks are maybe acceptable, they are still a lot higher than with Xience or a good metallic drug-eluting stent. So it's difficult for me to identify a population where it would be an advantage," she said.

Commenting to heartwire , Dr Ted Feldman (NorthShore University Health, Evanston, IL), who was not involved in the study, said the concept of a bioresorbable scaffold "remains attractive but the negative data continue to accrue."

He added, "We're still looking at the first-generation of bioresorbable, and the question is can industry see this development through."

The study was published March 29, 2017 in the New England Journal of Medicine.

It came just days after the ABSORB 3 investigators suggested the BVS scaffold should be avoided in smaller coronary vessels in response to an FDA alert to clinicians investigating a significantly higher risk of major adverse events observed over 2 years in ABSORB 3 — consistent with trends in ABSORB 2 and ABSORB JAPAN.

Nagging Scaffold Thrombosis

AIDA includes 1845 patients undergoing PCI at five high-volume centers in the Netherlands, about half of whom (54%) presented with acute coronary syndrome. Dual antiplatelet therapy was used in 89% of patients in each arm.

The AIDA data and safety monitoring board recommended early reporting of the data after the increased incidence of very late scaffold thrombosis came to light last fall in 3-year data from ABSORB 2.

The preliminary analysis identified a definite or probable device thrombosis rate about 3.5 times as high in the BVS scaffold group as that in the stent group over the 2 years (Kaplan-Meier 3.5% vs 0.9%; hazard ratio 3.87; 95% CI 1.78–8.42).

Definite/probable device thrombosis was higher with the BVS than the everolimus-eluting stent for all postimplantation periods: acute (<24 hours; 13 vs five patients), subacute (>24 hours to 30 days; eight patients vs one patient), and very late (>1 to 3 years; 10 vs two patients).

Notably, vessel size of <2.25 mm, adequate device sizing, and postdilation, performed in 74% the scaffold group vs 49% in the stent group, were not associated with scaffold thrombosis occurrence.

Implantation Technique

The authors specifically write that scaffold thrombosis occurred regardless of implantation technique, although lower rates of 1-year scaffold thrombosis have been reported when using a scaffold-specific strategy of predilation, adequate sizing, and postdilation.

Feldman pointed out that only a small proportion of cases in AIDA had routine intravascular ultrasound and routine postdilation, a point also emphasized in the FDA letter to clinicians.

"So given the limitation of this study experience, we're seeing that without careful attention to vessel prep, sizing the stent, and postdilation, the results are suboptimal," he said.

Asked by heartwire how big of an influence these issues had on the outcomes, Wykrzykowska said, "It's difficult to say" but pointed out that the study was designed to look at routine clinical practice in an all-comer population and that this does not include the use of optical coherence tomography (OCT) or intravascular ultrasound.

"If you haven't prepared the lesion well and you end up with an undersized or oversized or underdeployed device, then it's extremely difficult to correct that with postdilation no matter what your balloon size is," she said.

"OCT can help you to see if you've done a good job, but if you see on OCT that you're still not getting an optimal result, then you probably have to cover that area with a metallic stent."

Challenges with Absorb placement were reflected in significantly longer procedure times than with the Xience metallic stent (49 vs 44 minutes), more contrast material used (160 vs 151 mL), and a lower likelihood of receiving the assigned device (96.9% vs 99.8%).

Extending DAPT

As a result of the overall findings, the safety monitoring board recommended extending DAPT to 3 years in the BVS group. In ABSORB 2, no cases of very late scaffold thrombosis were seen in 63 patients who did not interrupt DAPT for up to 3 years, Wykrzkowska noted.

Feldman said it seems like a reasonable recommendation to extend DAPT given that scaffold thrombosis appears to extend beyond 2 years.

But, he stressed, "This is all based on judgment, and you appreciate how miserably complex it's been to figure out duration of dual antiplatelet therapy in standard drug-eluting stents, and here we're working in an even more complex situation with fewer data."

In a related editorial[2], Dr Debabrata Mukherjee (Texas Tech University Health Sciences Center, El Paso) writes that the longer DAPT duration "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.

"Because the current generation of metallic drug-eluting stents is associated with excellent outcomes, there is little rationale to use bioresorbable vascular scaffolds at this time."

Commenting to heartwire , Dr Renu Virmani (CVPath Institute, Gaithersburg, MD), who also was not involved in the study, said, "The results of the AIDA study give us further confirmation that concerns about scaffold thrombosis with Absorb are real and that further work is needed to understand the mechanisms by which it is occurring."

She continued, "We must always remember Absorb is a first-generation device that is limited by its bulky design. Many companies are working on future scaffold designs with thinner struts and less surface area. If the radial strength of these new-generation devices can be maintained, their behavior in humans will be better."

A final analysis is planned for AIDA, but at this point, Wykrzkowska said data from AIDA, ABSORB-2, ABSORB-3, and ABSORB JAPAN have taken away many of the putative advantages of the disappearing Absorb BVS scaffold. There isn't less long-term scaffold thrombosis or angina, there's an up-front higher risk of scaffold thrombosis, and the device is more difficult and labor-intensive to place.

"You start to lose the argument," Wykrzkowska said. "It's not like the first-generation Cypher, which gave you a huge 30% reduction of in-stent restenosis over the bare-metal stent. It seems like you sort of take risks for uncertain benefits, and that's really making me take a pause and think maybe we should go back to the drawing board to figure out what it is that we don't understand about how these devices behave."

AIDA was funded by Abbott Vascular. Wykrzykowska reports receiving a research grant from Abbott Vascular during the conduct of the study and personal fees from Abbott Vascular outside the study. Disclosures for the coauthors are listed in the paper. Feldman reports consulting for Abbott Vascular and Boston Scientific. Mukherjee reports no relevant financial relationships.

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