To evaluate the protective effect of IPC on the myocardial microcirculation response through IMR and the predictive value of IMR on the degree of myocardial reperfusion and the prognosis of patients.

This study is a clinical randomized controlled study, applying index of microcirculatory resistance (IMR) to evaluate the myocardial protection of ischemic postconditioning (IPC) in patients receiving direct PCI treatment for acute myocardial infarction.IMR is a quantitative evaluation index of microcirculation status. IPC has been reported to reduce ischemia-reperfusion injury and has a myocardial protective effect.The research plan divides patients into IPC and non-IPC groups at random. After the infarction-related artery is successfully implanted with a stent, the pressure guide wire is used to measure IMR and CFR in the state of maximal expansion of the microcirculation induced by intravenous ATP infusion.And analyze whether there are differences in indicators between the two groups and the relationship between these indicators and the patient's myocardial level reperfusion, cardiac function and prognosis.The purpose is to evaluate the myocardial protection of IPC and the predictive value of IMR on the degree of myocardial reperfusion and the prognosis of patients. It is expected that the target IPC can improve the IMR value, and IMR can predict the degree of myocardial reperfusion and cardiac function and prognosis.

Inclusion Criteria:

• Age ≥ 18 years old, no gender limit;
• First episode of STEMI (diagnostic criteria: ischemic chest pain lasting ≥30min; ST-segment elevation in two or more adjacent leads on the ECG or new left bundle branch block; with or without elevated myocardial markers), The onset time is within 12 hours, and emergency interventional treatment is planned;
• Agree and cooperate to participate in this research.

Exclusion Criteria:

• Old myocardial infarction;
• Killip grade of cardiac function ≥ grade III or cardiogenic shock;
• Systolic blood pressure ≤100mmHg;
• Bradycardia, HR<60pbm, or AVB above II degree;
• Past history of asthma or severe COPD;
• Severe liver and kidney dysfunction.