Intravascular ultrasound study of the effect of beta-emitting ((55)Co) stents on vascular remodeling and intimal proliferation.

The aim of this study was to evaluate vessel remodeling after implantation of high-activity (mean, 41.1 +/- 1.2 microCi) beta-emitting ((55)Co) stents. Proton bombarding in cyclotron has brought the radioactivity. Intravascular ultrasound (IVUS) investigation has been completed in 10 patients. The angiographies performed at 6 months revealed restenosis > 50% in five cases (50%). IVUS analysis demonstrated an absence of remodeling behind the stent, with no changes in total vessel volume (TVV; 353.6 +/- 126.3 and 343.9 +/- 90.6 mm(3)) or plaque + media volume (PMV; 171.7 +/- 57.4 and 166.8 +/- 42.6 mm(3)). On the other hand, lumen volume (LV) within the stent decreased significantly from 181.9 +/- 80.2 to 154.6 +/- 45.2 mm(3) (P < 0.02). This was due to presence of neointimal hyperplasia (NIH) at both extremities of implanted stents. No chronic recoil of the implanted stents was found. The analysis of edges (5 mm distally and proximally to the last stent struts) showed no significant changes in TVV (187.3 +/- 62.60 and 176.9 +/- 53.5 mm(3)), but PMV increase significantly from 61.9 +/- 31.2 to 82.2 +/- 43.4 mm(3) (P < 0.04) and LV decreased from 125.2 +/- 40.7 to 94.7 +/- 22.0 mm(3) (P < 0.02). In conclusion, single (55)Co radioactive beta-emitting stents with high initial activity are effective in reducing neointimal hyperplasia only within the stent body, as measured by IVUS, and they do not solve the problem of restenosis at the stent extremities as well as at the stent edges. Edge restenosis in this high radioactive stents was mainly (from 66%) due to neointimal proliferation.