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Six-month intravascular ultrasound (IVUS) measurements of the BVS bioabsorbable, everolimus-eluting stent show a higher degree of recoil compared to metallic-based drug-eluting stents (DES) that may be dependent on lesion morphology in the stented segment, according to a study in the November 11, 2008, issue of the Journal of the American College of Cardiology.
Researchers led by Nico Bruining, PhD, of Thoraxcenter/Erasmus Medical Center (Rotterdam, the Netherlands), looked at 16 patients in the first-in-man ABSORB trial who received the BVS (Bioabsorbable eVerolimus-eluting coronary Stent, Abbott Vascular, Santa Clara, CA) for single, de novo native coronary artery lesions. The stent has a backbone of poly-L-lactic acid that provides support and a coating of poly-D, L-lactic acid that contains and controls the release of everolimus. All components of the BVS except for 2 radio-opaque markers are expected to be fully absorbed in the human body within 2 to 3 years.
Researchers, though, had little knowledge about the mechanical behavior of BVS prior to its absorption. Using IVUS, Dr. Bruining and colleagues found an absolute stent recoil of 0.65 ± 1.71 mm2 with the bioabsorbable stent at 6 months, and a percent stent recoil of 7.60 ± 23.3% at the same time point.
By comparison, the authors note, absolute recoil and percent recoil are lower for metallic based stents such as Xience V (Abbott Vascular), which also elutes everolimus, and the original Palmaz-Schatz stent: 0.02 mm2 and 0.3% for Xience V at 6 months; 0.1 mm2 and 0.6% for Palmaz-Schatz at 4 months.
More Shrinkage with Calcified Lesions
Interestingly, both absolute recoil and percent recoil differed by lesion morphology in the stented segment, with calcified plaques resulting in significantly less late recoil than fibrocellular or fibronecrotic plaque types (table 1).
Table 1. Recoil at 6 Months by Plaque Type
0.74 ± 1.48
1.03 ± 2.12
0.20 ± 1.54
Percent Recoil (%)
8.90 ± 19.8
12.4 ± 28.0
1.97 ± 22.2
aP value for calcific vs. both other plaque types; P=NS for fibrocellular vs. fibronecrotic.
The researchers acknowledge that “it is obvious that the vessel scaffolding properties of the BVS have not been maintained for a long period compared with metallic stents,” and give some possible explanations. For one, polymer-based stents are more flexible than metallic stents, and may be more affected by the elastic properties of the arterial wall. In addition, since the BVS is designed to be gradually absorbed, the polymer backbone could weaken and lose its radial strength.
In an e-mail communication with TCTMD, Gregg W. Stone, MD, of Columbia University Medical Center (New York, NY), agreed that the recoil seen in the study is likely due to the BVS’s partial degradation over time and its lesser rigidity compared with metallic stents. “DES based on a metallic backbone (all others) have 0% recoil,” Dr. Stone noted, adding that recoil leads to late loss and restenosis, and can theoretically even predispose to stent thrombosis, “although stent thrombosis wasn’t seen in the first 30 patients with BVS.”
On IVUS follow-up, the study found late lumen loss with the BVS was 0.45 ± 0.39 mm, similar to that seen with the Taxus (Boston Scientific, Natick, MA) paclitaxel-eluting stent.
Lesion Morphology May Guide Decisions
In an e-mail communication with TCTMD, Dr. Bruining agreed that the amount of recoil seen at 6 months with the BVS stent needs to be reduced, adding that attention to lesion morphology may aid in determining where, or if, a bioabsorbable stent should be implanted, although more research is necessary to support this.
“There seems to be a suggestion that there is a relationship between stent performance and lesion morphology (composition) for the investigated BVS type of bioabsorbable stent,” Dr. Bruining said, adding that the current study also makes a case for increased use of IVUS. “A more methodological conclusion is that IVUS data (or imaging data) can provide more detailed information than only straightforward quantitative dimensional measurements,” he said.
In 2-year data from the ABSORB trial reported at TCT 2008, there was 1 ischemia-driven major adverse cardiac event, no cardiac deaths, no stent thrombosis, and no ischemia-driven target lesion revascularizations.