Background and Objectives: The mechanical problems contributing to in-stent restenosis (ISR) have been in the more spotlight in the drug-eluting stent (DES) era. However, all ISR lesions could not be explained by the mechanical problems. The aim of this study was to evaluate the incidence of mechanical problems, defined as stent underexpansion or fracture, and analyze the subset of patients without obvious mechanical problems on intravascular ultrasound (IVUS) in ISR lesions. Subjects and Methods: Those eligible for this study included patients with ISR on follow-up angiography after implantation of DES in two centers. Of these patients, we excluded ISR with edge stenosis, having the different mechanism of ISR. Fifty-nine patients in 68 lesions had intrastent-ISR. Of these lesions, IVUS-applicable 45 lesions made up with our study group. Results: Preliminary results of single center were as below; Of the 24 lesions (sirolimus-eluting stent restenosis; 19, paclitaxel-eluting stent restenosis; 5), stent underexpansion [minimal stent cross-sectional area (CSA) was < 5 mm² and < 4.5 mm² in cases of small coronary artery (reference vessel diameter [RVD] < 2.8 mm)] was observed in 13 lesions (54%) and stent fracture (defined as non-visualization of struts on IVUS at restenotic segments) was identified in the 3 lesions (13%). Mechanical problems were not related to 9 ISR lesions (38%), in which profound intimal hyperplasia within the stent occurred. Divided into two groups (group with or without mechanical problems), there was no clinical difference except for mean age (group without vs. group with mechanical problems; 69±8 vs. 61±7 years, p=0.04). The group without mechanical problems, had longer RVD (3.2±0.3 vs. 2.6±0.3 mm, p <0.01), larger external elastic membrane CSA at minimal lumen diameter (12.9±1.5 vs. 10.1±2.6 mm², p <0.01) and larger neointimal hyperplasia CSA (5.2±1.7 vs 2.1±0.9 mm², p<0.01). Conclusions: The incidence of mechanical problems contributing to ISR was 62% in preliminary result of our study. The remaining one-third (38%) lesions were not related to mechanical factors. Further data including total study population of two centers will be presented later.
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