We used data submitted to the Yonsei OCT registry, evaluating neointimal coverage in patients who underwent coronary stent implantation for de novo lesions.12,13 General exclusion criteria for the follow-up OCT study were as follows: 1) untreated significant left main coronary artery disease, 2) apparent congestive heart failure, 3) renal insufficiency (baseline creatinine ≥2.0 mg/dL), and 4) lesions unsuitable for OCT imaging (vessel size ≥3.5 mm or lesions within 10 mm of the ostium of a major epicardial artery). Between September 2007 and October 2010, a total of 242 patients with 268 lesions were selected from the OCT registry database. Inclusion criteria of the current study comprised lesions treated with EES, Bx-ZES, sirolimus- or paclitaxel-eluting stents, as well as those followed with a follow-up OCT examination at 12±4 months after stent implantation. Exclusion criteria were 1) bifurcation treated with 2-stent techniques, 2) angiographic evidence of restenosis, 3) lesions with repeated revascularization, 4) bare-metal stent implantation, and 5) poor OCT image quality. Second-generation DESs were deployed in 103 patients for 119 lesions including EES (Xience V™, Abbott Vascular, Santa Clara, CA, USA) and Bx-ZES (Endeavor Resolute®, Medtronic, Santa Rosa, CA, USA), while first-generation DESs were implanted in 139 patients for 149 lesions including sirolimus-eluting stents (Cypher™, Cordis, Miami, FL, USA) and paclitaxel-eluting stents (Taxus™, Boston scientific, Natick, MA, USA). DES implantation was performed using current, conventional techniques, and the choice of DES was made according to the operators' discretion. After DES implantation, all patients received dual antiplatelet therapy with aspirin and clopidogrel until the follow-up OCT was conducted. This study was approved by the Institutional Review Board of our institute, and written informed consent was obtained from each patient.

Detailed explanations regarding the OCT system and methods for imaging have been described in our previous studies.12,13 OCT examination was performed using a conventional OCT system (Model M2 Cardiology Imaging System, LightLab Imaging, Westford, MA, USA) with a motorized pull-back system at 1.0 mm/s. The occlusion catheter was positioned proximal to the stent, and a 0.014-inch wire-type imaging catheter (ImageWire, LightLab Imaging) was positioned distal to the stent. During image acquisition, the occlusion balloon (Helios, Avantec Vascular, Sunnyvale, CA, USA) was inflated to 0.4-0.6 atm, and lactated Ringer's solution was infused at a rate of 1.0 mL/s. The imaging wire was pulled from distal to proximal, and continuous images were acquired and stored digitally for subsequent analysis.12,13 OCT analysis was performed by an independent investigator blinded to patient and procedural information.

Cross-sectional OCT images were analyzed at 1-mm intervals (every 15 frames). Stent and luminal cross-sectional areas (CSAs) were measured at 1-mm intervals, and NIH CSA was calculated as the stent CSA minus the luminal CSA. Percent NIH CSA was calculated as NIH CSA×100/stent CSA. Mean values are reported in this study. The thickness of NIH, defined as the distance between the endoluminal surface of neointima and the strut, was measured inside the struts at a line as perpendicular as possible to the neointima and strut.10 An uncovered strut was defined as having a NIH thickness of 0 µm.10,14 A malapposed strut was defined as a strut that had detached from the vessel wall (Cypher™, ≥160 µm; Taxus™, ≥130 µm; Endeavor Resolute®, ≥110 µm; Xience™, ≥100 µm).15,16 The percentage of uncovered or malapposed struts was investigated for evaluation of the healing responses of DESs as shown on OCT. The percentage of malapposed or uncovered struts in each stented lesion was calculated as the (number of malapposed or uncovered struts/total number of struts in all cross-sections of the lesion)×100, respectively. Cross sections with major side branches (diameter ≥2 mm) were excluded from this analysis. The neointimal coverage of stent struts in each cross-section was evaluated, and then the percentage of uncovered struts was analyzed and compared between the two groups. Intra-stent thrombi were defined as a signal-rich, low-backscattering protrusions or high-backscattering protrusions inside the lumen of the artery with signal-free shadowing on OCT images (dimension ≥250 µm).13

Quantitative coronary angiography analysis was performed using an offline quantitative coronary angiography system (CASS system II, Pie Medical Imaging, Nuenen, the Netherlands) before and after stent implantation and at the follow-up angiogram. The minimal luminal diameter of the coronary lesions treated with DESs and a reference diameter were measured in the view that was the most severe and not foreshortened.

All statistical analyses were performed using the Statistical Analysis System software (SAS; 9.1.3., SAS Institute, Cary, NC, USA). Categorical data were presented as a number (%) and compared with Chi-square statistics or Fisher's exact test. Continuous data were presented as mean±standard deviation and compared with Student's t-test. Comparisons among the four different DESs were performed by analysis of variance with post-hoc analysis by the Bonferroni method. If the distributions were skewed, a non-parametric test was used. A value of p<0.05 was considered statistically significant.

This study has several limitations. First, selection bias might affect the results because this was a non-randomized registry study. Second, because this study was not a controlled comparative one, direct comparisons among four different DESs could not be performed. However, there were no significant differences in the baseline clinical and angiographic parameters between the two groups. Third, because the study population of the current study was free of major adverse events after DES implantation until follow-up OCT, the lesions of this study might not represent those seen in real world practice. Fourth, in this study, the first-generation DES group, which consisted of sirolimus-eluting stents and paclitaxel-eluting stents, was compared with second-generation DESs. However, because sirolimus-eluting stents and paclitaxel-eluting stents showed different outcomes in some pathologic and imaging studies,12,13,23,24 careful attention must be given when interpreting the results. Finally, no clinical follow-up data was provided due to the short duration of clinical follow-up after OCT evaluation.

In conclusion, this follow-up OCT study showed that second-generation DESs characteristically had greater neointimal coverage than first-generation DESs. For more definite conclusions, long term clinical and serial OCT follow-up with a larger population will be needed in the future.