目的 探讨急性ST段抬高型心肌梗死（STEMI）患者发病昼夜时相与急诊经皮冠状动脉介入治疗（PCI）术后心肌缺血再灌注损伤（MIRI）严重程度之间的关系。 方法 回顾性分析2021年1月至2025年12月 扬州大学附属医院收治的于发病12 h内行急诊PCI的STEMI患者共362例。依据症状发作时间将患者分为夜间组、清晨组、午后组和傍晚组。比较各组术后肌酸激酶同工酶（CK-MB）、心肌肌钙蛋白I（cTnI）峰值水平、术后即刻冠状动脉TIMI血流分级、无复流/慢血流发生率、术后7 d左室射血分数（LVEF）及术后7、30 d内主要不良心血管事件（MACE）发生率。采用Kruskal-Wallis检验或单因素方差分析进行组间比较，多元线性回归分析发病昼夜时相对心肌损伤标志物的独立影响，二元logistic回归分析无复流的独立危险因素。 结果 夜间组与清晨组的CK-MB及cTnI峰值显著高于午后组与傍晚组（P 0.05）。夜间组无复流/慢血流发生率最高（24.3%），显著高于午后组（9.7%，P = 0.018）。术后7 d LVEF在夜间组最低（51.3 ± 7.8）%，午后组最高［（57.2 ± 6.4）%，P 0.05）］。校正缺血总时间、梗死部位、Killip分级等混杂因素后，多元线性回归显示夜间及清晨发病仍是cTnI峰值升高的独立预测因素，logistic回归显示夜间发病是无复流/慢血流发生的独立危险因素。 结论 STEMI患者急诊PCI术后MIRI严重程度与发病昼夜时相相关，夜间发病患者心肌损伤更重、微循环障碍更多、早期心功能更差。该效应在校正混杂因素后仍然存在，提示发病昼夜时相是MIRI严重程度的独立影响因素，可作为急诊PCI术后MIRI风险评估的辅助参考因素。

Objective To investigate whether the circadian timing of symptom onset influences the severity of myocardial ischemia-reperfusion injury （MIRI） following primary percutaneous coronary intervention （PCI） in patients with acute ST-segment elevation myocardial infarction （STEMI）. Methods This retrospective study included 362 consecutive STEMI patients who underwent primary PCI within 12 hours of symptom onset at the Affiliated Hospital of Yangzhou University between January 2021 and December 2024. Patients were stratified into four circadian groups based on symptom onset time： nighttime， morning， afternoon， and evening. Primary outcomes included peak creatine kinase-MB （CK-MB） and cardiac troponin I （cTnI） levels. Secondary outcomes encompassed post-PCI TIMI flow grade， incidence of no-reflow phenomenon， left ventricular ejection fraction （LVEF） at 7 days， and major adverse cardiovascular events （MACE） at 7 and 30 days. Group comparisons used Kruskal-Wallis or one-way ANOVA tests as appropriate. Multivariable linear and logistic regression models identified independent associations between circadian timing and myocardial injury markers or no-reflow risk. Results Peak CK-MB and cTnI levels were significantly higher in the nighttime and morning groups compared with the afternoon and evening groups （all P 0.05）. The nighttime group exhibited the highest incidence of no-reflow phenomenon （24.3% vs. 9.7% in the afternoon group， P = 0.018）. LVEF at 7 days was lowest in the nighttime group （51.3 ± 7.8） % and highest in the afternoon group ［（57.2 ± 6.4）%， P = 0.003］. After adjustment for total ischemic time， infarct location， and Killip class， nighttime and morning onset remained independent predictors of elevated peak cTnI. Nighttime onset was independently associated with no-reflow risk. Conclusions The circadian timing of symptom onset is independently associated with MIRI severity following primary PCI for STEMI. Patients with nighttime onset experience greater myocardial necrosis， higher rates of microvascular obstruction， and impaired early ventricular recovery. These findings suggest that circadian biology may modulate ischemia-reperfusion pathophysiology， supporting the integration of symptom onset timing into risk stratification protocols for STEMI management.