Biodegradable Stents: Future or Fancy?
——Live Interview with Professor Maurice Buchbinder
<International Circulation>: The purpose of designing biodegradable stents is to resolve problems including both early intimal hyperplasia of BMS and late in-stent thrombosis of DES. How wide is the gap between the dream of solving all these problems and the present reality?
Dr. Buchbinder: In modern day stenting you must have two things. You must have neo-intimal hyperplasia drug response to minimize restenosis and with DES you must have a low acute， sub-acute， and long term thrombogenicity， namely low SAT (low sub-acute thrombosis) rates. In order to mitigate against sub-acute thrombosis， we have now subjected patients to both aspirin and ticlopidine or aspirin and Plavix dual antiplatelet therapy for a long time and we think that 1~2 years is a minimum duration of therapy. The DES are now effective， but are they as safe as we would like them to be? In some cases， you must interrupt dual antiplatelet therapy because they have a bleed or are scheduled for surgery. What may happen when you stop dual antiplatelet therapy there may be acute thrombosis at that time and closure of the stent upon interruption， especially if that interruption occurs within the first 12~months. The dream with biodegradable stents is that you can within 9~12 months maximum no longer have a prosthesis and therefore the you will be able to interrupt and stop these antiplatelet agents because the stent has done its job， treated the lesion， minimized hyperplasia because of the drug is coated with， and disappears after having done its job. It disappears and promotes healing of the treatment site with normal and functioning endothelium. Therefore， the real story with biodegradable stents is not that they are better prostheses to keep the vessel open or armed with better drugs to fight neo-intimal hyperplasia but they allow the disappearance of the prosthesis and allow more complete healing of the treated area of the vessel and so are healing promoters. This makes the area more normal and there is less chance of thrombosis. In fact， the two year data from the Rotterdam group on the only clinically tested biodegradable stent， which is from Abbott and is called the Absorb stent， has shown that at two years endothelium function is virtually indistinguishable from the normal segment and more importantly plaque volume throughout the vessel has decreased because the vessel has grown appropriately and has expanded well in a healthy manner to allow more blood flow. Thus， the early effect of stenting has worked but most importantly the healing response and late endothelial function at two years has returned to normal and that has never been seen with any metal prosthesis that is durable.
<International Circulation>: What is your view of the approach of using a biodegradable polymer coating only?
Dr Buchbinder: The reason that a biodegradable stent could be better is the fact that you are still left with a bare metal stent in the artery and therefore the endothelial function at that spot is not normal. It is endothelialized but it is not functioning as well as it would with a normal non-metallic stented segment. I think there will be an evolution and we will try to understand how to adjust dual antiplatelet therapy duration， how to withdraw antiplatelet therapy， etc. The next phase will be biodegradable polymers that perhaps can obviate the need for very strict dual antiplatelet therapy. Thirdly， once data from fully biodegradable stents is released then we can call the fully biodegradable stents third generation stents. Third generation stents by design are thicker and not as nimble and may not necessarily be used in every lesion. We will probably be using a hybrid approach.
<International Circulation>: What is the main aspect of biodegradable stents that requires further study?
Dr. Buchbinder: We need to know when in man that they actually degrade. Some studies have shown that between 9~16 months they are mostly degraded. Once they degrade， recovery of endothelial function， plaque volume regression， and positive remodeling of the vessel are all fertile areas for investigation and proof of concept.
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