BACKGROUND: Plaque rupture (PR) and subsequent thrombus formation is the most important mechanism leading to an acute myocardial infarction (AMI). Distal embolization and no-reflow during percutaneous coronary intervention (PCI) carries a poor prognosis in AMI patients. It is unclear which factors are associated with no-reflow after PCI in AMI patients with PR. OBJECTIVES: The aim of this study was to investigate the predictors of the no-reflow phenomenon after PCI in AMI patients with PR. METHODS: The study group comprised 112 AMI patients who underwent stent implantation and pre- and post-PCI IVUS examinations. Angiographic no-reflow was defined as TIMI flow grade 0, 1, and 2. IVUS findings included multiple ruptured plaques (PRs separated by a >5-mm length of artery containing smooth lumen contours), thrombus (had a layered lobulated appearance, evidence of blood flow within the mass, and speckling or scintillation), and plaque prolapse (tissue extrusion through the stent struts). RESULTS: Of 112 patients who underwent pre- and post-stenting IVUS, no-reflow was observed in 17 patients (15.2%). High-sensitivity C-reactive protein (hs-CRP) was significantly higher (6.2짹6.0 mg/dl vs. 2.2짹2.9 mg/dl, p=0.002) and baseline TIMI flow grade was significantly lower in no-reflow group (TIMI flow grade <3: 59% vs. 18%, p<0.001). Lesion site plaque plus media area was significantly greater (12.9짹2.6 mm2 vs. 10.8짹4.2 mm2, p=0.009), remodeling index was significantly higher (1.14짹0.17 vs. 1.03짹0.20, p=0.031), and the presence of IVUS-detected thrombus (88% vs. 56%, p=0.012), culprit lesion multiple plaque ruptures (71% vs. 37%, p=0.009), and plaque prolapse (65% vs. 34%, p=0.015) were significantly more common in no-reflow group. In the multivariate analysis, plaque prolapse (HR=33.02; 95% CI 3.38-322.75, p=0.003), hs-CRP (HR=1.03; 95% CI 1.01-1.05, p=0.013), and culprit lesion multiple plaque ruptures (HR=15.73; 95% CI 1.61-153.46, p=0.018) were independent predictors of post-PCI no-reflow in AMI patients with PR. CONCLUSIONS: Elevated hs-CRP and IVUS-detected multiple plaque ruptures and plaque prolapse are associated with post-PCI no-reflow in AMI patients with PR.