Abstract: Objective To explore the value of triglyceride-gluscose (TyG) index in evaluating the severity of coronary artery lesions and long-term major adverse cardiovascular events (MACE) in patients with acute coronary syndrome (ACS) and diabetes mellitus (DM). 
Methods The medical records of gender, age, TyG index, degree of coronary artery lesions (SYNTAX score), and occurrence of MACE in 142 patients with ACS and DM were collected. The Pearson correlation test was used to analyze the correlation between TyG index and SYNTAX score. The receiver operating characteristic (ROC) curve was used to analyze the evaluation value of TyG index for the severity of coronary artery lesions. The COX regression model was used to analyze the influencing factors of long-term MACE. 
Results Of 142 patients with ACS combined with DM, there were 56 patients with severe coronary artery lesions (severe group) and 86 patients with mild coronary artery lesions (mild group). The TyG index and glycosylated hemoglobin of the severe group were higher than those of the mild group (P＜0.05). Pearson correlation analysis showed that there was a positive correlation between TyG index and SYNTAX score (P＜0.05). ROC curve analysis showed that the area under the ROC curve (AUC) of TyG index to evaluate disease severity was 0.863, the optimal cutoff value was 7.73, and the specificity and sensitivity were 80.4% (45/56) and 84.9% (73/86) respectively. Among the 142 patients, 4 patients were lost to follow-up, and 138 patients completed the follow-up, including 15 patients (11.11%) developing cardiogenic death, 8 (5.80%) developing recurrent angina, 5 (3.62%) developing recurrent myocardial infarction, 4 patients developing heart failure (2.90%), and 2 patients receiving target vessel reconstruction (1.45%), with a total of 34 (24.64%) patients with MACE. Age, TyG index and glycated hemoglobin of the MACE group were higher than those of the non-MACE group, and left ventricular ejection fraction （LVEF） was lower than that of the non-MACE group (P＜0.05). COX regression model analysis showed that LVEF, age, TyG index, and glycated hemoglobin were all influencing factors of long-term MACE, and the risk of MACE events increased significantly with decreased LVEF level and increased age, TyG index and glycated hemoglobin in ACS patients with DM (P＜0.05). 
Conclusion The TyG index is positively correlated with the severity of coronary artery lesions in patients with ACS and DM, which is an independent risk factor for long-term MACE and can be used to predict the risk of MACE. 

Key words: acute coronary syndrome, diabetes mellitus, triglyceride-glucose index