SUCJECTS AND METHODS: A two-year follow-up IVUS was performed in 30 patients with patent ISR segments at the 6-monthly follow-up angiography. Serial IVUS images were acquired at 5 equidistant intra-stent sites and 3 different reference segment sites (1, 2 and 4 mm from stent margin).

RESULTS: The mean intra-stent IH area and IH burden significantly increased between 6 and 24 months-from 2.1±1.1 to 2.6±1.4 mm2 (p<0.001) and from 26±10 to 33±14% (p<0.001), respectively. There were significant decreases in the mean external elastic membrane (from 10.1±3.9 to 9.7±3.9 mm2, p=0.015) and lumen area (from 5.6±2.3 to 5.1±2.3mm2, p=0.021) within the distal reference segments between 6 and 24 months. Target lesion revascularization (TLR) was performed between 6 and 24 months in 6 patients (20%) following the beta-irradiation therapy. There were no significant differences between the TLR and non-TLR groups, with the exception of a smaller minimum lumen CSA at 24 months in the TLR group.

CONCLUSION: Because of a small amount of late loss between 6 and 24 months, most irradiated ISR vessel segments remained stable for up to 2 years. However, quantitative evidence of late catch-up was evident in most patients and was significantly associated with 24-month TLR in some patients with a smaller minimum lumen area.