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™ (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 endoluminal deformability of the stented vessel.

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