BIORESORBABLE STENT A FUTURE OF STENT BUSINESS

BIORESORBABLE STENT

Over the past several years at TCT, there has been a focus away from traditional metallic drug-eluting stents (DES) to these bioresorbable scaffold technologies as the next step in stent evolution. However, recent trial data, especially from the ABSORB III Trial, and the first commercial bioresorbable stent being pulled off the market on Sept. 14, 2017, has dampened that view.

The latest round of trial data for the Abbott Absorb everolimus-eluting bioresorbable vascular scaffold (BVS) at TCT shed light on why the company announced last September it was pulling the stent off the market. Data from several ABSORB trials statistically showed good performance compared to the market-leading Xience everolimus-eluting metallic stent. However, there was signal in the data for slightly poorer outcomes, negating any long-term benefits the stent might offer. Experts involved in the trials said Absorb saw a very low usage rate, with estimates of U.S, usage of less than 5 percent.

A key prediction for interventional cardiology coming out of recent Transcatheter Cardiovascular Therapeutics (TCT) and American College of Cardiology (ACC) meetings is that bioresorbable stents will eventually replace conventional metallic stents in the coming years. Experts say dissolving stents have their drawbacks compared to metallic stents, but as the technology continues to advance, these issues may be resolved. Even if they are not, experts say growing clinical data shows the benefits of bioresorbable stents may outweigh any drawbacks.

Most bioresorbable stents are made of polylactic acid, a naturally dissolvable material that is used in medical implants such as dissolving sutures. The drawbacks of using polymer include recoil after expansion, stent thickness causing maneuverability and crossing issues, difficulty visualizing a non-metallic stent on fluoroscopy and stents not crimping firmly on delivery balloons. 

However, the advantage is not implanting a permanent metal prosthesis. Since the stent disappears, it eliminates the cause of potential inflammation that can lead to late-stent thrombosis and restenosis. Once the stent dissolves after about two years, it restores the vessel to a natural state of vasoconstriction and vasodilatation. The disappearance of the device also leaves open all options if future interventions are needed.

Coronary stents are used in percutaneous coronary intervention (PCI) procedures for the treatment of coronary heart disease. Stents are tube-like devices that are used to open and widen clogged heart arteries. Bioresorbable stent (BRS) devices, also known as bioabsorbable or biodegradable stents, refer to coronary stents that can fully dissolve in the body. The main advantage and promise of using a BRS is that it will clear out of the body within a few years, thereby theoretically reducing the long-term adverse effects normally seen with conventional stents.

Percutaneous coronary intervention (PCI) with bioabsorbable stents has created interest because the need for mechanical support for the healing artery is temporary, and beyond the first few months there are potential disadvantages of a permanent metallic prosthesis. Stents improve immediate outcomes, including profoundly reducing acute vessel occlusion after PCI by scaffolding intimal tissue flaps that have separated from deeper layers and by optimizing vessel caliber. They limit restenosis by preventing negative remodeling. The intimal hyperplastic healing response to PCI that contributes to restenosis, especially after bare metal stenting, can be limited by coating stents with antiproliferative medications.

Potential advantages of having the stent disappear from the treated site include reduced or abolished late stent thrombosis, improved lesion imaging with computed tomography or magnetic resonance, facilitation of repeat treatments (surgical or percutaneous) to the same site, restoration of vasomotion, and freedom from side-branch obstruction by struts and from strut fracture-induced restenosis. Bioabsorbable stents have a potential pediatric role because they allow vessel growth and do not need eventual surgical removal. The progression of stenosis seen within stents 7 to 10 years after stenting has been attributed, at least in part, to inflammation around metallic struts, which might argue for an absorbable stent. Progression is also observed late after balloon angioplasty. Some patients say they prefer an effective temporary implant rather than a permanent prosthesis.