Background:Previous studies revealed that culprit vessels of ST-segment elevation myocardial infarction (STEMI) were often related to mild or moderate stenosis.However,recent studies suggested that severe stenosis was primarily found in culprit lesions.The objective of this study was to analyze the stenosis severity of culprit lesions in STEMI patients and to clarify the paradoxical results.Methods:A total of 489 consecutive STEMI patients who underwent primary percutaneous coronary intervention were retrospectively studied from January 2012 to December 2014.The patients were divided into three groups based on stenosis severity using quantitative coronary analysis:Group A,314 cases,stenosis ≥70％;Group B,127 cases,stenosis 50-70％;and Group C,48 cases,stenosis ＜50％.The clinical,demographic,and angiographic data of all groups were analyzed.Results:Patients in Group A exhibited a significantly higher prevalence of history of angina pectoris (95.9％ vs.62.5％,P ＜ 0.00l),multivessel disease (73.2％ vs.54.2％,P =0.007),and lower cardiac ejection fraction (53.3 ± 8.6 vs.56.8 ± 8.4,P =0.009) than those in Group C.Multivariable analysis revealed that history of angina pectoris (odds ratio [OR]:13.89,95％ confidence interval [CI]:6.21-31.11)and multivessel disease (OR:2.32,95％ CI:1.25-4.31) were correlated with severe stenosis of the culprit lesion in Group A.Conclusions:Most culprit lesions in STEMI patients were severe stenosis.These patients exhibited a higher prevalence of angina history and multivessel diseases.