Optical coherence tomography (OCT) shows that implantation of either bioresorbable scaffolds (BRS) or bare-metal stents (BMS) stimulates neointimal tissue to cover and help stabilize high-risk plaque. Unlike BMS, however, BRS expand over time to accommodate the increase in neointimal tissue, thereby preserving lumen size.

The findings, published online October 14, 2014, ahead of print in EuroIntervention, suggest that BRS may have a future role in invasively sealing vulnerable plaques, the authors say.

Serial OCT Reveals Plaque Coverage, BRS Expansion

Mean lumen area decreased between baseline and short-term follow-up (6-12 months) in both groups, although the reduction was considerably smaller in scaffolded segments compared with stented segments (-1.34 vs -2.11 mm²; P = .026), a finding the researchers attributed to increased neointima in the BMS group.

At midterm follow-up (24-36 months), the scaffold had expanded (from 7.67 to 8.28 mm²; P < .001) and accommodated the increased neointima area (from 1.38 to 2.17 mm²; P < .001), so that the lumen area remained unchanged (P = .571). No evidence of neoatherosclerosis was seen in any of the device segments.

At baseline, 12 thin-cap fibroatheromas (TCFAs) were detected in scaffolded segments, 11 in stented segments, and 10 in native segments. Initially, there was no difference in minimum cap thickness among the segment groups. At short-term follow-up, only 1 TCFA in the scaffolded segments and 3 in the stented segments remained (P = .231). At midterm follow-up, all TCFAs in the scaffolded segments were fully covered, while 6 TCFAs were still present in native segments at a mean follow-up of 24 months.

At short-term follow-up, neointima thickness covering TCFAs and calcific spots was higher in the BMS segments compared with BRS segments. But neointima thickness continued to develop in BRS, and when BRS at midterm follow-up were compared with BMS at 6 months, no difference in thickness was observed.  

In addition, the lipid plaque burden index did not change at follow-up in the scaffolded, stented, and native segments.

Impact on Calcification Unclear

Although there was no difference in the number of calcific spots between baseline and follow-up for either the BRS or BMS segments, both groups showed reductions in the calcific plaque burden index at short-term follow-up. The researchers caution, however, that this apparent improvement is likely due to the neointima masking deeply embedded calcific spots that were visible at baseline.

In a model predicting neointima thickness, follow-up time and device type both played roles, with lower thickness at short-term follow-up and for BRS (P = .040 and P = .006, respectively), but underlying plaque morphology had no effect. 

Three lesion-related events occurred in the BRS group—2 non–Q-wave MIs over the short term and 1 TLR at midterm—while 2 TLR procedures at short-term follow-up were reported in the BMS group.

Dr. Serruys and colleagues highlight the key role of OCT in analyzing the effects of BRS vs BMS. The imaging modality’s high resolution enables more accurate characterization of superficial plaque and assessment of neointima thickness over various tissues than does either IVUS or IVUS-virtual histology, they observe.

The lack of a DES group appears to be a limitation of this comparative study, the authors acknowledge. However, they point out, even though drug elution reduces neointima formation in the short term, at midterm the tissue response to DES is similar to the response to BMS. Thus, the lumen area is likely to be compromised by these permanent metallic devices, just as it is with BMS.  

Transforming Thin Caps Into Thick Caps

“This study nicely shows that the Absorb bioresorbable scaffold has the capability to turn a thin-cap fibroatheroma (vulnerable plaque) into a thick-cap fibroatheroma, which should translate into improved long-term lesion stability,” Gregg W. Stone, MD, of Columbia University Medical Center (New York, NY), told TCTMD in an email.

“The special nature of the scaffold is that it is able to expand with the native vessel over time to accommodate additional neointimal growth, which should minimize restenosis,” he explained. “And unlike metallic DES, bioresorbable scaffolds allow restoration of physiologic vascular responses (eg, cyclic pulsatility with blood flow and ability to vasodilate during exercise and other conditions). In this regard, [the] BVS may be a superior long-term solution to [the limitations of] metallic DES, but large studies will be required to prove this.”

It is “premature to advocate an invasive sealing of vulnerable plaques based on the findings of this analysis,” the authors caution, adding that further research is needed to identify more accurately future culprit lesions and the timing of erosion or rupture.

Dr. Stone noted that the Absorb BVS is currently being tested in PROSPECT ABSORB, the first randomized trial to examine whether the device might be an effective therapy for stabilizing vulnerable plaque. The primary endpoint is enlarged lumen area at 2 years, he reported, adding, “If positive, this study will then need to be followed by a large-scale randomized trial to prove the value of this approach.”

Source:
Bourantas CV, Serruys PW, Nakatani S, et al. Bioresorbable vascular scaffold treatment induces the formation of neointimal cap that seals the underlying plaque without compromising the luminal dimensions: a concept based on serial optical coherence tomography data. EuroIntervention. 2014;Epub ahead of print.

Disclosures:

• Dr. Serruys reports no relevant conflicts of interest.
• Dr. Stone reports serving as a consultant to REVA and co-principal investigator for the PROSPECT II trial.

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