No-reflow phenomenon is one of the most serious complications during elective percutaneous coronary intervention (PCI) and causes myocardial infarction unexpectedly. Purpose: The purpose of this study is to determine the most important plaque feature in the development of no-reflow phenomenon after elective coronary stent implantation. Methods and results: We evaluated 353 atherosclerotic lesions using threedimensional integrated backscatter intravascular ultrasound (IB-IVUS) before elective

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... onary stent implantation. These lesions were categorized into three groups according to the coronary blood flow after stent implantation (Group N, T, and P). Group N included 334 lesions (94.6%) without no-reflow phenomenon during elective PCI. Group T and P included 12 lesions (3.4%) with transient noreflow phenomenon and 7 lesions (2.0%) with persistent no-reflow phenomenon, respectively. We investigated patients' characteristics, angiographic findings and IB-IVUS findings. There were no significant differences about patients' backgrounds and laboratory findings among three groups. No-reflow phenomenon occurred predominantly in the most severe lesions (Type C), which represented 12%, 25%, and 57% of lesions in Group N, T, and P (p=0.014), respectively. There was no significant difference in the ratio of lipid component in target lesions (Group N/T/P: 54±15/58±17/61±13%, p=0.28). In contrast, Group T and P had larger true lipid volume significantly compared with Group N (Group N/T/P: 97±79mm 3 /166±112mm 3 /238±181mm 3 , p<0.0001). Multivariate analysis revealed that only true lipid volume in target plaque was the significant predictor for the development of no-reflow phenomenon. The odds rate for no-reflow phenomenon was 4.82 per 50mm 3 increase in lipid volume (95% confidence interval 1.72-16.0, p=0.0056). Conclusion: Lipid volume in target plaque is the only predictor for the development of no-reflow phenomenon. In Atherosclerotic plaque analysis using threedimensional IB-IVUS, quantitative evaluation is more important to estimate the risk of no-reflow phenomenon compared with qualitative evaluation.