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Polymeric stents: Degradable but strong

Coronary stents have rapidly evolved from the early hand-crimped endoprosthesis into low-profile, highly reliable devices. Currently, available coronary stents permit the treatment of complex cases with a wide safety margin and a high likelihood of optimal acute results [1]. Much, if not most, of the popularity of coronary stents is due to the fact that these devices provide the means for a trustful and predictable interventional procedure, which is basically a function of the mechanical properties of modern stents and their delivery systems. It is, therefore, widely recognized that any new interventional device must aim to maintain the safety and predictability currently achieved with metallic coronary stents. The rationale of a bioabsorbable, polymer-based stent, is very appealing—a radiolucent stent that will be kept in the vessel only until it is needed, to be completely cleared out thereafter. In theory, bioabsorbable stents would preserve the good characteristics of traditional stenting without the undesirable drawback of a permanent metallic implant. There is the concern, however, that the mechanical properties of stents made of polymeric structures might not be optimal, because of their intrinsic differences from the characteristics of metallic alloys. In an important article in this issue of CCI, Tanimoto et al. report that the acute stent recoil was not different between bioabsorbable everolimuseluting coronary stents and everolimus-eluting cobaltchromium stents. As the authors point out, these findings may be an indication that the tested poly-L-lactic acid bioabsorbable stent may have good radial strength. Even though the findings presented by Tanimoto et al. are promising, their report also shows that the acute results of the tested bioabsorbable stent may be slightly inferior to its metallic counterpart. The mean postprocedure minimal lumen diameter was 2.30 mm in the bioabsorbable group and 2.43 mm for the metallic stents (P 1⁄4 0.03). Whether this difference of 0.13 mm is of clinical relevance is debatable, especially in the context of drug-eluting stents for which further luminal losses are expected to be small in the long term [2]. However, it must be noted that the difference in acute luminal size was detected in cases of very low complexity. Clearly, the results of Tanimoto et al. warrant further investigations to evaluate if the differences between bioabsorbable and metallic stents will or will not be amplified when treating complex cases, where high radial strength are most needed, such as in ostial, calcified, angulated, and bifurcational lesions among others. Bioabsorbable stents are in their early days. To become the workhorse of interventional cardiology, these new devices must be proven safe and effective for a wide range of patient and lesion subsets. Together with their biological effects, enhanced mechanical characteristics are pivotal to ensure that bioabsorbable stents will be eventually added to the armamentarium of interventionalists.