Objective:To evaluate whether index of microcirculatory resistance(IMR)is associated with left ventricular(LV)remodeling in acute anterior ST elevation myocardial infarction(STEMI)pa-tients undergoing primary percutaneous coronary intervention(PPCI).Methods:This was a single-center retrospective cohort study.The patients with first anterior STEMI who received PPCI from January 2014 to August 2017 in Peking University Third Hospital was enrolled.After PPCI,IMR was measured immediately by using pressure/temperature guidewire.The success rate of IMR measurement was 100％.Also we collected some related clinical data from the medical records and laboratory results.Infarct size[assessed as creatine kinase(CK)peak],echocardiography at baseline and 1 year follow-up were as-sessed.LV adverse remodeling(LVAR)was defined as ≥20％increase in LV end-diastolic volume(LVEDV).Results:A total of forty-three patients were enrolled,with an average age of(58.7±12.4)years.The patients were divided into two groups as IMR ≤25 and IMR＞25 by normal values recommen-ded by previous literature.Compared with IMR ≤25 group,IMR＞25 group had a higher percentage of initial thrombolysis in myocardial infraction(TIMI)grade 0(95.7％vs.65.0％,P=0.029),higher serum CK peak value[4 090(383,15 833)vs.1 580(396,5 583),P=0.004].The IMR＞25 group suffered higher rates of ventricular aneurysm(30.4％vs.5.0％,P=0.021).There was no difference in LVEDV[(111.0±18.8)mL vs.(115.0±23.6)mL,P=0.503]between the two groups 1 day after MI,but after 1 year,LVEDV in IMR＞25 group was significantly higher than in IMR≤25 group[(141.5± 33.7)mLvs.(115.9±27.9)mL,P=0.018].The incidence of LVAR was more significant in IMR＞25 group(47.4％vs.11.8％,P=0.024).Binary Logistics regression showed that IMR[B=0.079,exp(B)(95％CI)=1.082(1.018-1.149),P=0.011]and serum triglyceride level[B=1.610,exp(B)(95％CI)=5.005(1.380-18.152),P=0.014]were the predictors of LVAR 1 year after MI.IMR had a good predictive value for LVAR 1 year after MI[area under the curve(AUC)=0.749,P=0.019],IMR＞29 was a good cutoff value with sensitivity 81.8％and specificity 68.0％.Conclusion:Our study elaborates that immediate measurement of IMR after PPCI in patients with STEMI can reflect the microvas-cular function.And IMR could be used as a quantitative biomarker to predict LVAR after STEMI.