Abstract: Objective  To investigate the changes and significance of microRNA-326(miR-326) in peripheral blood mononuclear cells in patients with acute coronary syndrome(ACS) after percutaneous coronary intervention(PCI). 
Methods  A total of 205 ACS patients treated in Beijing Luhe hospital affiliated to Capital Medical University were selected prospectively as the study subjects. Density gradient centrifugation was performed to obtain mononuclear cells in peripheral blood; real-time fluorescence quantitative PCR was used to detect the level of miR-326 in mononuclear cells. Cox regression analysis and restrictive cubic spline were used to analyze the relationship between miR-326 and the prognosis of ACS patients. 
Results  The level of miR-326 in the poor prognosis group and the good prognosis group showed an increasing trend with time(P＜0.05). The area under the receiver operating characteristic(ROC) curve(AUC) of the prognosis of ACS patients diagnosed with miR-326 at 7 d after PCI was higher than that before PCI and at 3 d after PCI, and  the differences were statistically significant(P＜0.05). The mean survival time of the high miR-326 group was higher than that of the low miR-326 group, and the difference was statistically significant(P＜0.05). Cox regression analysis showed that miR-362［HR=0.039, 95%CI: 0.016-0.098, P＜0.05］ was an independent protective factor for the prognosis of ACS patients(P＜0.05). miR-362 was related to the prognosis of ACS patients(P＜0.05), and had a nonlinear relationship(P＜0.05). When miR-326<0.24, as compared with miR-326=0.24, the risk of poor prognosis was increased; when miR-326>0.24, as compared with miR-326=0.24, the risk of poor prognosis was decreased.
Conclusion  miR-326 at 7 d after PCI is associated with the prognosis of ACS patients. Low miR-326 levels at 7 d after PCI suggest a higher risk of poor prognosis.

Key words: acute coronary syndrome, microRNA-326, percutaneous coronary intervention