Background:
Although sirolimus-eluting stent (SES) has significantly reduced in-stent restenosis by inhibiting neointimal hyperplasia, insufficient neointimal coverage after stenting may result in adverse outcomes. Determinants of neointimal coverage following SES, however, are poorly understood.
Methods:
We evaluated 28 SES lesions using both angioscopy and intravascular ultrasound (IVUS). Degree of neointimal coverage was judged by angioscopy at follow-up (11 ± 6 months):
complete/incomplete
coverage, based on whether the stent struts were embedded by the neointima. Minimal stent area (MSA), external elastic membrane (EEM), lumen cross-sectional area (CSA) and plaque burden (EEM minus lumen/EEM CSA) were measured by IVUS at stent implantation. Both proximal and distal references were used. Stent expansion was assessed by stent expansion index (SEI) as MSA/reference EEM CSA. Under-expansion was defined as SEI < 0.4. Incomplete apposition was defined as the lack of contact between any strut and the underlying vessel wall.
Results:
Complete
coverage was identified in 10 (36%), and
incomplete
coverage in 18 (64%). Time from the stenting to angioscopy (10 ± 5 versus 11 ± 7 months, p=0.8) as well as the lesion and procedural characteristics was similar between the
complete/incomplete
coverage groups. IVUS parameters were also similar, except for the final MSA (7.0±1.8mm
2
in
complete
versus 5.3±1.9mm
2
in
incomplete
, p=0.02) and lumen CSA at the distal reference site (6.1±1.4mm
2
in
complete
versus 4.9 ±1.2mm
2
in
incomplete
, p= 0.02). The frequency of incomplete apposition was similar between the groups (20% in
complete
versus 39% in
incomplete
, P= 0.4); however, SEI was significantly larger in the
complete
coverage than in the
incomplete
coverage group (0.52 ± 0.11 versus 0.39 ± 0.09, p=0.002). Stent under-expansion was identified only in 2 (20%) of the
complete
coverage, as compared to 67% of the
incomplete
coverage group (P=0.046). By multivariate logistic regression analysis, large SEI was strongly associated with
complete
neointimal coverage (P=0.04).
Conclusion:
Optimal expansion of the stent is a major contributor to the complete neointimal coverage following sirolimus-eluting stent implantation.