Feature Of The Week 6/14/09: Assessing Sirolimus-Eluting Stent Implantation by Optical Coherence Tomography
Feature Of The Week 6/14/09: Heart disease is a leading cause of death in the industrialize world. Since the early 1990's when the Palmaz bare medal stent was introduced, stents have continued to play a major role in the treatment of heart disease. The stent market is over $5B and there is intense pressure to improve stent technology from both a healthcare and market share perspective. Optical Coherence Tomography is unique in its ability to provide critical information in assessing the impact, safety, and efficacy of stents. Some recent work by researchers at Kobe University and Stanford University address factors in thrombus formation associated with sirolimus-eluting stents.
Although sirolimus-eluting stents (SES) have reduced the incidence of restenosis, late thrombosis, a life-threatening complication, has emerged as a major concern in the clinical setting. According to recent angioscopic analyses, the presence of subclinical thrombus in SES is more common than the clinical incidence of stent thrombosis. However, local determinants of thrombus formation and its clinical significance under antiplatelet therapy are still unclear.
Several studies have shown that asymmetric stent expansion may affect the pattern of neointimal growth presumably through uneven drug delivery. Since delayed arterial healing characterized by exposed stent struts is considered a possible risk for thrombosis, we hypothesized that asymmetric stent expansion could affect thrombus formation after SES implantation.
In this study, we evaluated 53 patients (53 lesions) using optical coherence tomography (OCT) 6 months after SES implantation. Fourteen cases of thrombus (26%) were detected by OCT (Thrombus: n=14 vs. Non-thrombus: n=39). The percentage of cases with thrombus were associated with longer stents, larger number of uncovered struts, smaller average Stent expansion index (SEI: minimum / maximum stent diameter), and greater average neointima unevenness score (NUS: maximum neointimal thickness in the cross-section / average neointimal thickness of the same cross-section). A significant relationship existed between average SEI and average NUS (P<0.0001, R=0.68), and between average SEI and the number of uncovered struts (P<0.0006, R=0.46). There was no significant difference in MACE during follow-up (median: 485days, 7.1% vs. 12.8%, P>0.99).
In this OCT study, longer stent length and greater asymmetric stent expansion were found to be determinants of thrombus formation following SES implantation. Asymmetric stent expansion may interfere with even neointimal coverage of the stent surface after SES deployment, perhaps a key mechanism for thrombus formation. The implications of this study suggest the clinical utility of additional imaging modalities to ensure that intracoronary stents are properly and fully deployed so patients are not subjected to the risk of future thrombus formation.