Long-term follow-up evaluation after sirolimus-eluting stent implantation by optical coherence tomography: do uncovered struts persist?

s w t o t n t b w o the Editor: Presently, occurrence of late stent thrombosis (LST) fter drug-eluting stent implantation is a major clinical concern. lthough LST is an infrequent complication, LST can lead to erious results. A long-term follow-up study revealed recently that ST occurs at a constant rate of 0.6%/year for up to 3 years after rug-eluting stent implantation (1). Regarding pathological coniderations, a delayed arterial healing characterized by incomplete ndothelialization and persistence of fibrin plays a key role in the ccurrence of LST. Moreover, the best morphometric predictor of ST after drug-eluting stent implantation is a ratio of uncovered truts to total struts/section of 0.3 (2). Therefore, we hypotheized that the uncovered struts of sirolimus-eluting stent (SES) emain for an extended period of time. Optical coherence tomography (OCT) with high-resolution mages (approximately 10 m) can clearly distinguish thin neoinimal hyperplasia (NIH) on stent struts and uncovered struts (3). o date, no long-term OCT follow-up data after SES implantaion are available. The present OCT examinations focused on the requency of uncovered struts of the SES at 2-year follow-up. Between February 2007 and May 2007, 2-year angiographic nd OCT follow-up examinations after SES (Cypher, Cordis orp., Miami Lakes, Florida) implantation were performed for 21 egments in 21 patients (age 64 10 years, 18 male). During this tudy period, clopidogrel had not been approved for clinical use in apan. The OCT procedure has been previously reported (3). Crossectional OCT images were analyzed at intervals of 1 mm. hickness of NIH inside all struts was measured, and thickness m was defined as uncovered. Uncovered strut ratio in each ross-section was calculated as uncovered strut ratio uncovered trut(s)/total struts (Fig. 1). In-stent thrombus was defined as an rregular mass protruding into the lumen that had dimension 250 m at its thickest point. Continuous data are presented as ean SD. Fisher exact test or unpaired t test was used for tatistical analysis. In 485 cross-sectional images, 3,707 struts were identified. hickness of NIH was 71 93 m. Frequency of uncovered struts as 5% (range 0% to 12%/patient). In the bifurcations, of the 39 truts located in the orifice of side branches 4 (10%) were ncovered. In the overlapping segments, 19 of 286 (7%) struts ere uncovered. Prevalence of patients who had any uncovered truts was 81%. Uncovered strut ratio/patient ranged from 0 to .43. Frequency of cross-section(s) with uncovered strut ratio 0.3 as 2%. Concerning these cross-sections, 2 were in the overlaping segments and none was in the bifurcation. Prevalence of atients who had any cross-sections with uncovered strut ratio 0.3 was 38% (Fig. 2). The OCT identified 3 thrombi in 3 patients. There were no bnormal findings on coronary angiograms. None of these cases howed any clinical thrombus-related events. Among these paients, 2 received dual antiplatelet therapy and another patient was rescribed aspirin monotherapy. Uncovered struts or cross-sections ith uncovered strut ratio 0.3 were recognized in 1 patient. In our series, 2% of the uncovered struts in 81% of the patients till remained 2 years after SES implantation. These frequencies ere higher than in bare metal stents (0.1% of the struts in 7% of he patients; Takano et al., unpublished data). Moreover, 38% f the patients had the cross-section of uncovered strut ratio 0.3, he most powerful pathological predictor of LST. However, o thrombotic events occurred in any patient. There was a possibility hat existence of these cross-sections was not an absolute condition ut a necessary condition for the occurrence of LST. In other ords, under the condition of existence of these poorly covered