• Interventional Techniques & Devices

• Interventional Techniques & Devices
• Cardiology

The development of metalic stents improved outcomes after angioplasty by reducing acute vessel occlusion. However, permanent metal-based stents have the potential for negative sequelae after several months in place that couls be overcome if the stents were absorbable. Mohammad I. Kurdi, MBBS, Al Takhassoussi Hospital, Riyadh, Saudi Arabia, reviewed the advantages of having stents “disappear” and discussed profress toward development of the idea bioabsorbable stent.

Reabsorbable stents could reduce or eliminate stent-associated thrombosis, obstructions caused by stent strut side-branches, and restenosis subsequent to strut fracture. Resorption could also allow reestablishment of vascular function. After stent absorbtion, the stented site could be more easily imaged using computed tomography or magnetic resonance and re-treated if necessary, either surgically or via percutaneous coronary intervention (PCI) prodcedures, although the expectation is that repeat interventions would be avoided. Furthermore, bioabsorbable stents could be used to treat pediatric patients, allowing the treated vessels to grow without requiring surgical removal of the stents.

The concept of bioabsorbable stents has been around for over 2 decades, but there are challenge to development. Ideal bioabsorbable stents must be strong enough to function for an appropriate time, have struts that are not too thick, be capable of delivering anti-proliferative drugs to control restenosis, and not cause unacceptable inflammation during breakdown. The long-term use of antiplatelet therapy that is required with conventional stents, which is expensive and does not eliminate all late-occurring thrombosis, could be avioded with bioabsorbable stents.

Features of five of the bioabsorbable stents in development are listed in Table 1.

To summarize, the ideal bioabsorbable stent should be easy to handle and implant, and be detectable by imaging to ensure accurate post-dilatation and placement of additional stents without gaps or overlaps. Having a detectable absorbable stent also means that complete resorption can be confirmed. In addition, at implantation, bioabsorbable stents should have an initial strength similar to that of conventional metal stents and be able to maintain this strength for sufficient time to help overcome the early negative remodeling forces that occur soon after PCI, this negative remodeling is the main cause of restenosis after balloon angioplasty. Stenting via PCI also causes an intimal hyperplastic or excessive healing response, hence the need for a stent that is capable of releasing antiproliferative drugs. Ideally, repair with a bioabsorbable stent would achieve and maintain vessel movement, increase blood vessel lumen size, and produce a reduction in plaque area. In addition, it would be desirable to regain appropriate physiologic responses to exercise and the ability to dilate in response to local ischemia in healed arteries.

The ideal bioabsorbable stent should also result in a healed, normally functioning vessel with no foreign body (stent) remaining, and no restenosis or late thrombosis development. Early encouraging results, particularly the results from the bioresorbable vascular scaffold everolimus-eluting bioabsorbable poly-L-lactic acid stent, although they require confirmation in larger clinical trials in patients with complex lesions, suggest the ideal bioabsorbable stent can be developed.

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