IVUS radiofrequency analysis in the evaluation of the polymeric struts of the bioabsorbable everolimus-eluting device during the bioabsorption process

Background: In the ABSORB study cohort A the changes in the amount of dense calcium and necrotic core have not been reported in comparison to the prestenting phase; this evaluation could be useful to better clarify the bioabsorption process. Aim of this study was therefore to evaluate the dynamic changes in plaque size and plaque tissue composition observed between 6 months and 2 years follow-up, and to compare these findings to the prestenting phase. Methods: Angiography, intravascular ultrasound and derived parameters (virtual histology, palpography, and echogenicity) were serially assessed postprocedure, at 6 months and at 2 years in 20 patients. In a subset of 8 patients the same measurements were also recorded in the prestenting phase. Results: In the total population a reduction of 18% in the plaque area was observed between 6 month and 2 year follow-up (7.56 ± 2.32 mm² at 6 months vs. 6.16 ± 2.10 mm² at 2 year follow-up; P < 0.01). In the subgroup of eight patients who underwent IVUS during the pre-stenting phase, the plaque area at 2 year follow-up was not significantly different when compared to the prestenting plaque area (7.29 ± 2.29 mm² at prestenting vs. 7.48 ± 1.45 mm² at 2 year follow-up, P 5 NS). Necrotic core area was reduced by 24% between the 6 month and 2 year follow-up (0.97 ± 0.66 mm² at 6 months vs. 0.74 ± 0.53 mm² at 2 year follow-up; P 5 NS), whilst dense calcium was reduced by 14% from 6 month to 2 year follow-up (0.83 ± 0.50 mm² at 6 months vs 0.72 ± 0.64 mm² at 2 year follow-up; P 5 NS). Whilst the necrotic core at 2 years follow-up was not significantly different when compared to the pre-stenting phase (0.62 ± 0.42 mm² prestenting vs 1.07 ± 0.56 mm² at 2 year follow-up; P 5 NS), the area of dense calcium was significantly higher at follow-up compared to prestenting (0.35 ± 0.35 mm² pre-stenting vs. 0.84 ± 0.66 mm² at 2 year follow-up; P < 0.05). Conclusions: The reduction in the necrotic core component between 6 month and two year followup could be related to a synergistic effect of the bio-absorption process and the antiinflammatory action of everolimus.