Are Polymer-Free Durable Stents The Perfect Stent?
We want to address the potential benefits of polymer-free durable stents. One of the primary advantages may be that they avoid the adverse effects of long-term polymer exposure. In fact the first Cook drug-eluting stent (DES) design was a polymer free stent. Theoretically they should improve healing and endothelialization. They may allow an improvement of the stent-vessel surface and therefore eliminate delamination which has been one of the problematic points with polymer coatings. There is a potential, as we have seen with all bio-absorbables, for a shorter duration of dual antiplatelet therapy. A few small studies have examined vessel reactivity and seem to show vessel responsiveness at late follow up which indicates a return of function to the vessel wall. The polymer-free durable stents come in several varieties and we don’t have the allotted time to really discuss the composition of each stent, however, most of these are basically bare metal stents that have had some surface modification allowing the surface to either be roughened or otherwise to have materials applied to the stent surface. There has been an evolution in the design, starting from porous surfaces and moving to solid gels with silicate or nanofilms, etc..
Gaps in the current knowledge
The main issue is this: Will polymer-free stents reduce the incidence of very late stent thrombosis, thereby lessening the need for long term dual anti platelet therapy? And if so, is there a penalty to pay in terms of target lesion and target vessel revascularization? These are the advantages with current bio-compatible durable polymers or complete bio-absorbable DES designs. In fact, new iterations of EES and ZES have really markedly changed the game in terms of the lower rates of restenosis and stent thrombosis. Furthermore, a reduction in dual antiplatelet therapy is possible as we have seen already in Europe where duration of dual antiplatelet therapy is routinely only six months after implantation of a Xience stent.
But, we must keep in mind that the current experiences with these polymer-free stents is limited, and there are relatively small numbers of studies and relatively small numbers of patients. Despite the fact that some of these have achieved CE mark, we certainly don’t yet have large studies in multiple patient populations, nor do we have late outcomes that show that the non-polymeric DES with surface modifications can change late stent thrombosis. To date, there has been only one randomized study, although promising. The study compared a polymer free stent to Cypher in over 1000 patients and presented 3-year follow up. The very late stent thrombosis rate was lower with the Biosensors non-polymer as compared to the Cypher, suggesting that the lack of the polymer leads to a lower VSLT rate, but again this is only one study.
Summary and Recommendations
We believe that the concepts embodied with this kind of stent are very attractive. Many patients in the US cannot afford Plavix and Prasugrel due to cost; so one of the things that this kind of stent could do is dramatically decrease the length of duration of clopidogrel or dual antiplatelet therapy. We would like to see results using 6 versus 3 months or 6 versus 1 year of clopidogrel therapy with these types of stents. In conclusion, the latest DES designs with durable biocompatible polymers have shown promise in reducing the incidence of stent thrombosis as well improved efficacy compared to the first-generation DES. More trials and more patients are needed to properly define their benefit.
Speaker: Steve Bailey
Moderator: Alfredo Rodriguez
Panelists: Jorge Belardi, Ariel Duran