Assessment of the absorption process following bioabsorbable everolimus-eluting stent implantation: temporal changes in strain values and tissue composition using intravascular ultrasound radiofrequency data analysis A substudy of the ABSORB clinical trial

Aims: The main objective was to use IVUS-backscatter radiofrequency (IVUS-RF) to assess the degradation of a bioabsorbable stent by measuring serial changes in dense calcium (DC) and necrotic core (NC) as assessed by intravascular ultrasound-Virtual Histology (TM) (IVUS-VH) and in the strain as assessed by palpography. Methods and results: In the ABSORB trial, 27 patients treated with a single bioabsorbable everolimuseluting stent (BVS, Abbott Vascular, Santa Clara, CA, USA) were all imaged with IVUS-RF post-stenting and at 6-month follow-up, and 13 and 12 patients were also investigated pre-stenting with IVUS-VH and palpography respectively. From pre- to post-stenting, with VH (n=13), there was an increase in mean DC (9.8 vs. 25.4%, p=0.0002) and NC (15.5 vs. 30.5%, p=0.0002). In palpography (n=12), the mean number of frames with Rotterdam Classification (ROC) III/IV per cm decreased from 1.22 +/- 1.91 to 0.12 +/- 0.31 (p=0.0781) and the mean cumulative strain values (all frames with ROC I-IV scores) changed from 0.50 +/- 0.27 to 0.20 +/- 0.10% (p=0.0034). Comparing post-stenting with follow-up (n=27), VH showed a decrease in DC (29.7% vs. 21.1%, p=0.0001). NC also decreased (26.9 vs. 21.5%, p=0.0027). For palpography (n=25 patients), an increase in the mean number of frames with ROC III/IV per cm was observed from 0.09 +/- 0.26 to 0.22 +/- 0.36 (p=0.1563) while the mean cumulative strain values (all frames with ROC I-IV scores) changed from 0.15 +/- 0.10 to 0.26 +/- 0.12% (p<0.0001). Conclusions: IVUS-VH changes at 6 months suggest alteration of the BVS with reduction of RF backscattering by polymeric struts. Strained plaques on the palpograms were almost abolished following stent implantation. However, strain values reappeared within 6 months suggesting an increase in endolumina I deformability of the stented vessel.