Tissue characteristics of neointima in late restenosis: integrated backscatter intravascular ultrasound analysis for in-stent restenosis.

Although late restenosis is one of the long-term complications of stent implantation, its pathogenesis has not been fully elucidated. For consecutive patients who developed in-stent restenosis (ISR) after stent implantation, integrated backscatter (IB) intravascular ultrasound was performed for ISR lesions. The tissue characteristics of neointima within the stented segment were compared between lesions with early restenosis and those with late restenosis. Of 73 ISR lesions arising after sirolimus-eluting stent (SES; n = 25) or bare-metal stent (BMS; n = 48) implantation, early and late restenosis were documented in 52 and 21 lesions, respectively. A higher prevalence of late restenosis was observed after SES implantation than after BMS implantation (60.0 vs. 12.5 %; p < 0.001). The duration between stent implantation and late restenosis was significantly shorter after SES implantation than after BMS implantation (57.0 ± 22.1 vs. 124.4 ± 19.6 months; p < 0.001). Percent low-IB volume was significantly higher in the neointima of late restenosis than in that of early restenosis (29.9 ± 9.9 vs. 19.8 ± 11.3 %; p < 0.001). Significantly more low-IB tissue was observed in the neointima of late restenosis than in that of early restenosis, suggesting atherosclerotic progression in late phase after stent implantation as a possible mechanism of late restenosis.