Long-term changes in neointimal hyperplasia following implantation of bare metal stents assessed by integrated backscatter intravascular ultrasound

In-stent restenosis (ISR) is a common phenomenon with bare metal stents (BMSs) in the early stage after implantation. However, ISR occurs at a lower rate with long time after BMS implantation. We assessed changes over time in neointimal hyperplasia following BMS implantation using integrated backscatter intravascular ultrasound (IB-IUVS). Thirty-six patients who received target lesion revascularization (TLR) to treat ISR were classified according to the duration of the interval between stent implantation and TLR: the early group (within first year n = 25) and the VL group (very late ISR ≥5 years, n = 11). IB-IUVS was used to evaluate within-stent sites from the proximal to the distal edge of the stent. IB-IVUS color maps were then constructed by tracing the stent struts and vessel lumen. Neointimal tissue was classified as high-IB (IB <−29 dB; a representative cord of calcification), middle-IB (−49 dB ≤ IB < −29 dB; fibrosis), or low-IB (−49 dB ≤ IB; lipid pool). We compared percent (%) volume, average %area of cross-sectional area (CSA), and %area of minimum CSA of each component between the groups. There were no significant differences in %volume, average %area of CSA, or %area of minimum CSA for the high-IB component between groups. The %low-IB components were 20.0 ± 8.8 % for volume, 20.1 ± 8.9 % for mean CSA, and 17.6 ± 8.5 % for minimum CSA in the early group. On the other hand, in the VL group, the %low-IB components were significantly increased to 31.8 ± 7.9 % for volume (p < 0.01 vs. the early group), 31.2 ± 7.6 % for mean CSA (p < 0.01 vs. the early group), and 33.1 ± 12.3 % for minimum CSA (p < 0.01 vs. the early group). By contrast, the %middle-IB component showed a reduction in extended time, with %volume of the middle-IB decreasing from 78.3 ± 8.1 to 66.4 ± 7.1 %, average mean %area of CSA from 78.2 ± 8.2 to 66.9 ± 6.9 %, and % area of minimum CSA from 80.7 ± 7.9 to 65.5 ± 11.4 % (p < 0.01;. the early vs. the VL group). Our results suggest that in-stent neointimal tissues developing over time consist of an increased low-IB component and a decreased middle-IB component and may contribute an increased of lipidemic component and a decreased of fibrotic component.