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Absorb bioresorbable vascular scaffolds (BVS) did not increase lumen size as much as bare metal stents did in the ABSORB II trial, a new analysis indicated.

The BVS failed to match Xience in reducing plaque area (-1.12 mm² versus -1.60 mm² for Xience, P=0.005) and plaque burden (-22.6% versus -25.9%, P<0.001), according to , of Imperial College London, and colleagues.

Accordingly, they reported in , acute gains at the site of the pre-procedural minimal lumen area (MLA) after stenting were lower in Absorb recipients (+3.46 mm² versus +4.27 mm², P<0.001), signaling a worse performance of the device. Outcomes in the lowest tertile were also more frequent in Absorb patients (risk ratio 3.04, 95% CI 1.94-4.76).

"At the site of the pre-procedural MLA, the increase of the lumen post-procedure was smaller in the Absorb arm than in the Xience arm. To achieve equivalent acute gain to Xience, the implantation of Absorb may require more aggressive strategies at implantation, pre- and post-dilation than the technique used in the ABSORB II trial," the authors concluded.

"Pre-dilation, optimal expansion, and avoidance of over-expansion are encouraged during the procedure with the Absorb device," they urged, "due to the difference in inherent device mechanical properties (i.e., tensile strength and radial force). Because the device balloon of the Absorb is semi-compliant, implantation with a high pressure might result in over-expansion of the device or edge dissection."

Yukinori Harada, MD, and , both of Munich's German Heart Centre, agreed that there is room for improvement on the part of the operator.

They wrote in an accompanying editorial, "At present, the additional pain associated with the implantation of current-generation bioresorbable stents must be borne by the operator. As we look to the future, however, manufacturers will shoulder more of this burden, with iterative development of this still young technology."

For now, operators have the task of "careful selection of lesions most likely to result in optimal scaffold expansion, meticulous attention to detail with respect to lesion preparation and post-dilation, and liberal use of intravascular imaging to identify and target suboptimal deployment," Harada and Byrne suggested.

The study from Serruys and colleagues included 445 out of the 501 patients enrolled in the ABSORB II trial. Participants were assessed by intravascular ultrasound (IVUS) before and after stent implantation.

Plaque morphology at the MLA cross-section was not associated with acute gain, they reported, though higher amounts of fibrotic plaque, necrotic core, and dense calcium were tied to lower acute gain in lumen area in both arms in univariate analysis.

Variables that were linked to low acute gain, in fact, include: absorb use, maximal inner device or balloon diameter throughout procedure, vessel and plaque areas at the MLA site, and negative remodeling.

Device expansion, defined as the ratio of post-procedural lumen area at the site of pre-procedural MLA to the expected inner device area calculated from the largest balloon used during procedure, was less robust in the Absorb than in the Xience (62% versus 71%, P<0.001). "This result might imply the necessity of more aggressive strategy during implantation and post-dilation of Absorb compared to Xience due to the device mechanical properties," according to Serruys' group.

Additionally, the main difference in acute gain in minimal lumen diameter was already apparent during device balloon expansion (+1.50 mm for Xience versus +1.23 for Absorb, P<0.01). Gains from post-dilation were similar between arms, despite less aggressive post-dilation in the Absorb arm. The investigators suggested that these findings "implied differences of the mechanical properties of both devices and the necessity of different procedural strategies for implantation."

Serruys and co-authors nonetheless pointed to the unblinded core laboratory staff as a major weakness of their study, as well as the failure to assess initial lesion geometry and morphology in approximately 12% of lesions.

Importantly, they added that they did not investigate "the relationship between IVUS findings and clinical events such as scaffold thrombosis that is our current concern after implantation of Absorb."

Absorb is awaiting an FDA approval decision following a favorable advisory panel vote in March.