BACKGROUND: Pre-treatment with statins decreased the incidence of cardiac enzyme increase after percutaneous coronary intervention (PCI) and distal embolization suspected to cause post-PCI myocardial damage. This study evaluated the effect of high dose atorvastatin pre-treatment on post-procedural index of microcirculatory resistance (IMR) values that are introduced for assessing the status of the microcirculation. This study was designed to enroll 200 patients for completion and we performed interim analysis. METHODS:. Sixty five patients with non-ST elevation acute coronary syndrome patients were randomly assigned to either high dose atorvastatin pre-treatment group(80 mg loading within 24 hours plus 40mg busting within 2 hours before PCI, n = 31) or control group(atorvastatin 10mg administration within 24 hours before PCI, n = 34). An intracoronary pressure/temperature sensor-tipped guidewire was used. Thermodilution curves were obtained during maximal hyperemia. The IMR was calculated from the ratio of the mean distal coronary pressure at maximal hyperemia to the inverse of mean hyperemic transit time. Creatine kinase-myocardial band(CK-MB) and CRP level was measured at baseline and at 12~24 hours after PCI. RESULTS: Patient���s baseline demographic and clinical characteristics were not significantly different. Post-PCI CK-MB (3.5짹10.3 vs 5.7짹15.2 ng/ml, p=NS) and CRP (0.23짹0.66 vs 0.41짹0.80mg/dl, p=NS) levels tended to be lower in patients with high dose group. Post-PCI IMR value tended to be lower in high dose group (17.6짹25.4 vs 22.4짹32.9, p=NS). CONCLUSIONS: Post-PCI measurement of the IMR tended to be lower in patients with high dose atorvastatin before PCI. This finding was derived from interim analysis of the study and more data are needed to verify the hypothesis.