Patients receiving BVS were younger than those with EES (54.0 ± 11.2 years vs. 61.7 ± 11.4 years, p = 0.012) and were smokers less frequently. The remaining baseline characteristics were comparable between the two groups (Table 1). The majority of treated lesions in both groups were simple lesions (type B1, 62 % in BVS vs. 70 % in EES group, p = 0.407).

Device and procedural characteristics are depicted in Table 2. Pre-dilatation was more frequently performed before BVS implantation and the diameter of the pre-dilatation balloon was larger in the BVS group (85 % vs. 58 %, p = 0.006 and 2.64 ± 0.51 mm vs. 2.34 ± 0.46 mm, p = 0.026, respectively), while BVS diameters were larger compared to those of EES (3.23 ± 0.34 mm vs. 3.07 ± 0.54 mm, p = 0.124). Lesion diameter stenosis was less severe in the BVS group and the inflation time was longer (81 ± 14 % vs. 89 ± 14 %, p = 0.023 and 44 ± 13 sec vs. 26 ± 8 sec, p < 0.001, respectively).

Whereas BVS were rapidly adopted in clinical routine, prospective data especially with regard to complex lesions are still rare [19‐21]. Recent data suggest that acute and late stent thrombosis are more frequent in BVS compared to DES [22], which is potentially associated with the unique mechanical properties of BVS. It has been shown that OCT is a valuable tool in determining post-procedural success with both BVS and DES as it potentially reduces late complications caused by mechanical shortcomings of the devices not detected when using angiography. This is the first OCT study comparing BVS and EES in a clinical routine setting.

The main finding of this study was that in a routine setting using no post-dilatation protocol, although gross device expansion of BVS and EES was comparable, device expansion uniformity of BVS, defined by SEI at the point of MLA, was significantly lower, whereas SSI was higher in BVS compared to EES (Fig. 1).

This lower device expansion can potentially contribute to an alteration in blood flow dynamics and can therefore represent a source for acute and subacute post-procedural complications as shown by Otake and coworkers [23]. Interestingly, this finding contradicts the study of Mattesini [14] but is in line with that of Brugaletta and coworkers in a substudy of the Absorb cohort B trial [24]. The most plausible explanation is that in the study of Mattesini a more aggressive vessel preparation with a balloon/artery ratio 1:1 and a stringent OCT guided post-dilatation balloon inflation strategy with non-compliant balloons were performed. In our study pre-dilatation was performed with in average 0.5 mm undersized balloons in 85 % of all cases and post-dilatation with NC-balloons was done only in 55 % of BVS implantations which is closer to the treatment procedure used in in the Absorb cohort B trial. Accordingly post-dilatation was performed in only 50 % of cases in the Ghost-EU trial, which included 1189 patients [25]. It is noteworthy that especially in the early phase the incidences of scaffold thrombosis were more frequent than anticipated in this study, which may be influenced by the low rates of post-dilatation (<40 %) in these patients with BVS failure. Although the lack of a stringent post-dilatation protocol is the most plausible cause for the discussed differences in SEI other contributing factors have to be considered. In contrast to our study, in which patients with ACS represented > 1/3 of the study population, they were not included in the study of Mattesini. In patients presenting with ACS, previous imaging analysis found more complex lesion morphologies when compared to patients with stable CAD [26]: Especially developing intramural hemorrhages is more common in acute lesions and because of the limited radial strength of BVS [13] they might not be able to withstand the consecutively increased vessel wall resistance (Fig. 2). The different post-procedural stent geometry was also supported by significant differences in the nominal vessel/proximal device ending diameter, where the proximal BVS ending was in average smaller and the proximal EES was in average larger than the native vessel diameter. This finding is in accordance with the study of Mattesini, where ISA at the proximal edge was more frequently observed in the BVS group. Although the clinical significance of ISA is not definitely determined, it has been associated with stent thrombosis in IVUS studies [27, 28]. In addition protruding struts at the proximal edge may complicate the advancement of other devices distal of the stent. However compared to DES the bioabsorbable technology has the potential advantage of ISA being at least only a temporary problem.

Although minimal lumen areas and rates of device underexpansion were comparable between BVS and EES, local radial expansion is significantly reduced in BVS in a clinical routine setting using no post-dilatation protocol. The clinical importance of this finding remains unclear and has to be evaluated in larger, randomized trials. However, a lower uniform expansion of the BVS could contribute to clinical events such as scaffold thrombosis and should be considered when implanting these devices. Considering the relatively low number of post-dilatations with non-compliant balloons in the BVS group our data further suggest that routine post-dilatation should be strongly considered.

ACS, acute coronary syndrome; BVS, bioresorbable vascular scaffold; CAD, coronary artery disease; DES, drug eluting stent; EES; everolimus eluting stent; FD, frequency domain; ISA, incomplete stent apposition; IVUS, intra vascular ultra sound, MACE, major adverse cardiovascular event; MLA, minimal lumen area; NC, non compliant; OCT, optical coherence tomography; SEI, stent eccentricity index; SSI, stent symmetry index.