OBJECTIVES: We present the remodeling index(RI) versus serial intravascular ul trasound(IVUS) data. BACKGROUND: The RI, derived by comparing lesion external el astic membrane(EEM) cross-sectional area versus the reference at one time point , is used in various IVUS studies as a substitute of true remodeling(change in E EM over time), assuming that it represents true remodeling. METHODS:We studied 4 6 non-stenotic left main arteries using serial IVUS(follow-up 18±8 months). P laques were divided into subgroups according to the follow-up RI: follow-up RI >1(n=27) versus follow-up RI ≤1(n=19). RESULTS: Lesions with a follow-up RI >1 had an increase in lumen despite an increase in plaque because of an increase in EEM. Conversely, lesions with a follow-up RI ≤1 had a reduction in lumen a s a result of both a plaque increase and EEM decrease. Overall, the follow-up R I correlated directly with changes in lesion site EEM(baseline-to-follow-up). Although there was no correlation between the follow-up RI and changes in refe rence EEM area, changes in reference EEM area did correlate directly with change s in lesion EEM area. In nearly 90%of lesions with a follow-up RI >1, there wa s a previously documented increase in EEM area. Using multivariate linear regres sion analysis, the follow-up RI was dependent on the baseline RI, the increase in lesion EEM area, and the decrease in reference EEM area. The follow-up RI wa s not dependent on changes in lesion plaque area. CONCLUSIONS: The vast majority of left main lesions with a remodeling index >1 had evidence of a previous incr ease in lesion-site EEM area. OBJECTIVES: We present the remodeling index (RI) versus serial intravascular ul trasound (IVUS) data. BACKGROUND: The RI, derived by comparing lesion external elstic membrane (EEM) cross-sectional area versus the reference at one time point, is used METHODS: We studied 4 6 non-stenotic left main arteries using serial IVUS (follow-up 18 ± 8 months) in various IVUS studies as a substitute of true remodeling (change in E EM over time) . P laques were divided into subgroups according to the follow-up RI: follow-up RI> 1 (n = 27) versus follow-up RI ≤ 1 (n = 19) had an increase in lumen with an increase in plaque because of an increase in EEM. Conversely, lesions with a follow-up RI ≤1 had a reduction in lumen asa result of both a plaque increase and EEM decrease. Overall, the follow-up RI correlated directly with changes in lesion site EEM (baseline-to-follow-up). Although there was no correlation between t he follow-up RI and changes in refe rence EEM area, changes in reference EEM area did correlate directly with change s in lesion EEM area. In nearly 90% of lesions with a follow-up RI> 1, there wa satially documented increase in m EEM area. Using multivariate linear regres sion analysis, the follow-up RI was dependent on the baseline RI, the increase in lesion EEM area, and the decrease in reference EEM area. The follow-up RI wa s not dependent on changes in lesion plaque area. CONCLUSIONS: The vast majority of left major lesions with a remodeling index> 1 had evidence of a previous incr ease in lesion-site EEM area.