Promising Outlook for Bioabsorbable Scaffolds, Polymers in Next-Generation Stents

MIAMI BEACH, FLA.—In the future of DES, Juan F. Granada, MD, of the CRF Skirball Research Center, Orangeburg, New York, and Jean-François Tanguay, MD, of the Montreal Heart Institute, suggested that bioabsorbable scaffolds and polymers are the next frontier.

However, in the same scientific symposium at TCT 2012, Elazer R. Edelman, MD, PhD, of Brigham and Women’s Hospital, Cambridge, Mass., hypothesized that strut dimensions, not polymer coatings, may be to blame for increased stent thrombosis risk.

Bioabsorbable polymers

According to Granada, the best approach is to get rid of the polymer as soon as possible. He claimed that the technological evolution of PCI has been a “Band-Aid developmental approach of putting one on top of another.”

Promising OutlookThe vascular response to DES implantation is a “complex and dynamic process influenced by multiple device-related factors,” he said. After implantation, drug elution is necessary to prevent restenosis and “overall, the biological response to emerging metals appears to be more favorable compared to best-in-class durable polymers,” Granada said. These polymers seem to delay surface endothelial cell coverage, induce higher levels of platelet activation and elicit a higher neointimal response in comparison to metallic surfaces.

However, “modified surfaces, like grooves, increase surface healing and decrease neointimal formation independent of the material surface,” he said. “The absence of polymer beyond the drug delivery period creates the potential to reduce the dependency on dual antiplatelet therapy for long-term safety, while maintaining best-in-class DES efficacy.”

Large randomized trials are still needed to confirm these hypotheses, Granada concluded.

Bioabsorbable scaffolds

During his presentation, Tanguay provided several potential patient benefits of using bioabsorbable vascular scaffolds. First, since restenosis is “a process limited in time,” he questioned the need for permanent stents. The new devices would also restore vasomotion properties and may improve long-term clinical outcomes, he suggested. Lastly, using bioabsorbable scaffolds might add options in dual antiplatelet therapy selection or duration.

“In theory, it makes sense for a patient to have a scaffold that would completely disappear,” he said.

Looking back, the “old rules” meant that for DES, “The goal was really to open the vessel, maintain the acute gain and then hope for [long-term safety],” Tanguay noted. But, the “new rules” with bioabsorbable scaffolds allow for the goal of providing “temporary vessel support and then allow [for] the physiology to evolve naturally.”

By balancing the polymer load and long-term absorption, he concluded, “a fully bioresorbable platform will happen very soon. This platform will allow vascular restoration therapy with return to vessel functionality. Such vascular scaffolds could become the dominant PCI strategy, and, if that doesn’t work, we always have the permanent DES platform.”

Answer may lie in the strut

After an overview of the literature regarding stent strut architecture, Edelman questioned the common thought that drug and polymer coatings increase acute stent clotting—when they might actually reduce thrombosis.

“The strut dimensions and the positioning of the stent, relative to the vessel wall, are absolutely critical in modulating stent thrombogenicity,” he said, adding that a better understanding of the role of the stent is needed.

Optimal stent geometries and surfaces, as previously demonstrated with thin stent struts, will “help reduce the potential for thrombosis despite complex stent configurations and variability in deployment,” Edelman concluded.

Disclosures
  • Dr. Edelman reports receiving financial support from numerous companies and the FDA.
  • Dr. Granada reports receiving grant/research support from Abbott Vascular, Amaranth, Boston Scientific Corporation and Medrad, consultant fees/honoraria from Medrad, and holding stock/equity in VNT.
  • Dr. Tanguay reports receiving grant/research support and consultant fees/honoraria from Abbott Vascular, AstraZeneca, Eli Lilly, GlaxoSmithKline and Roche.

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