Bioresorbable scaffolds represent the new revolution in interventional cardiology for the treatment of coronary artery disease . The benefits of this technology are very promising and may offset those of a metallic device, which is permanently implanted in the coronary artery. Bioresorbable stents may potentially offer additional benefits deriving from both restoration of normal vasomotor tone and from a late increase in lumen caliber due to positive vessel remodeling associated with stent degradation . The technique used for bioresorbable scaffold implantation is also different from that of a metallic stent, since predilatation is mandatory and postdilatation is often required. Therefore, particularities of this new implantation technique have to be acquired by the interventional physician.

Currently, two lactic acid–based devices have received CE mark approval for use in Europe: the everolimus-eluting Absorb stent (Abbott Vascular, Santa Clara, California) and the novolimus-eluting DESolve stent (Elixir Medical Corporation, Sunnyvale, California). The Absorb stent may receive approval from the US Food and Drug Administration by the first quarter in 2016. It is noteworthy that both devices have a strut thickness of 150 micron, as compared to the 80–100 micron of the second-generation metallic drug-eluting stent.

During the last years, an increasing amount of data from patients treated with these devices either in clinical trials or in clinical registries has become available. Overall, favorable clinical outcomes have been initially reported, especially in first-in-man and controlled clinical trials. However, several clinical registries of real-world patients have recently described a rate of stent thrombosis higher than that reported for second-generation metallic drug-eluting stents . It is of note that none of these trials or registries was sufficiently powered to detect differences in hard clinical endpoints and even less in a rare event, such as stent thrombosis. Nevertheless, this increased rate of scaffold thrombosis has generated some concerns in the interventional cardiology community.

Within this background the present report from Wiebe et al. in this issue of Cardiovascular Revascularization Medicine represents an attempt to explain the reasons for this concern. The investigators analyzed the outcomes of all the consecutive patients who have received Absorb implantation in their institution, dividing them into two groups according to the time of implantation (first 100 patients versus second 100 patients). Analyzing both groups with the same length of follow-up, they found a higher rate of major adverse cardiac events in the first group as compared to the second one. Whereas the two groups were comparable from the clinical point of view, the Absorb implantation was performed differently, with a higher rate of postdilation and of intracoronary imaging guidance in the latter group as compared to the former. The authors concluded that there was an evidence of a learning curve effect.

This finding is remarkable for many reasons. First, it may help explain the difference of event rates between the controlled trials and the registries beyond the fact that lesions included in the registries may be more complex. The inclusion of a patient in a controlled trial indeed requires the operator to pay much attention at the time of Absorb implantation, by the use of higher rates of lesion preparation and postdilatation and refined sizing . Second, this may be the first time that a learning curve effect is demonstrated for a coronary stent. It is clear that as the majority of the reported scaffold thrombosis cases seem to occur during the first 30 days, the procedural acute result is of utmost importance, especially because it can be influenced by the expertise of the operator.

However, the reasons that guided the operators to postdilate and to use imaging techniques more often are unclear. Besides, imaging parameters used by the operators in order to optimize the Absorb implantation were not clarified. In contrast, the GHOST-EU registry failed to show a learning curve effect, and the rates of postdilatation and intracoronary imaging–guided Absorb implantation were higher in the first patients enrolled as compared to the last ones . This particular finding, which went in the opposite direction to that observed in the current report, was speculatively explained by the increasing confidence of the operators in using the Absorb device. For these reasons, it is difficult to understand whether the increased use of postdilatation and imaging technique really resulted from a learning curve or from good common sense, considering the thickness of these devices (150 micron).

Postdilatation of a coronary stent after its implantation and use of intracoronary imaging are simple tools, which should be performed in most of the patients, regardless of the stent implanted, especially in complex lesions . The balloon on which the scaffold is mounted is indeed a compliant balloon, with not enough radial force to homogenously appose the struts on the vessel wall, especially in the event of spotty calcification. Therefore, the use of a noncompliant balloon, which applies the same radial force over its entire length, is usually recommended in order to improve strut apposition. Taking into account the reduced radial force of a bioresorbable scaffold as compared to that of a metallic stent, postdilatation should be considered much more in this particular scenario. Intracoronary imaging technique may, in this regard, guide the postdilatation and help sizing the noncompliant balloon and the final scaffold stent .

In conclusion, careful implantation with optimization of the procedural result is vital for these devices. In this sense, a magical recipe with the use of these devices is warranted: a European consensus trying to help the operators on how to select and how to implant such devices has been recently published . It will be interesting to see if the future advent of scaffolds with thinner struts may further change the implantation technique.