This study is a prospective, multicenter, randomized controlled clinical trial designed to evaluate the safety and efficacy of the coronary sinus balloon pump (manufactured by Shanghai MicroPort Rotapace Medical Technology Co., Ltd.) as an adjunctive therapy during percutaneous coronary intervention (PCI) in patients with acute ST-segment elevation myocardial infarction (STEMI). As a pivotal study, it aims to support the product registration application to the National Medical Products Administration (NMPA).

Inclusion Criteria:

General Inclusion Criteria:

1. Subjects aged ≥18 and ≤80 years, clinically diagnosed with ST-segment elevation myocardial infarction (STEMI).

2. Left ventricular ejection fraction (LVEF) ≤50% and ≥35% as assessed by echocardiography or left ventriculography prior to PCI.

3. Symptoms of myocardial infarction (e.g., persistent chest pain, with or without shortness of breath, nausea/vomiting, profuse sweating, dyspnea, syncope) consistent with the timing of myocardial ischemia, with symptom onset within 24 hours.

4. Electrocardiographic evidence of acute anterior wall myocardial infarction, defined as ST-segment elevation ≥1 mm (0.1 mV) in at least two contiguous precordial leads on a 12-lead ECG. For leads V2 or V3, the following gender- and age-specific cutoffs apply:

   • 2 mm (0.2 mV) in men ≥45 years old.
   • 2.5 mm (0.25 mV) in men <40 years old.
   • 1.5 mm (0.15 mV) in women.

5. Subject is eligible for primary percutaneous coronary intervention (primary PCI).

6. Subject is able to understand the purpose of the study, voluntarily agrees to participate by signing the informed consent form acknowledging the risks and benefits described therein, and is willing and able to comply with the required clinical follow-up procedures.

Angiographic Inclusion Criteria:

1. The target lesion is located in the proximal or mid segment of the left anterior descending artery (LAD).
2. TIMI flow grade of the target vessel is 0, 1, or 2 prior to PCI treatment.

Exclusion Criteria:

1. Presence of an implant or foreign body within the coronary sinus.
2. The target lesion involves the left main coronary artery, or there is a ≥50% stenosis in the left main coronary artery.
3. Known allergy or contraindication to drugs or materials required during PCI and the use of the investigational device (including, but not limited to, sirolimus, dual antiplatelet therapy drugs, polyamide, polyurethane, polytetrafluoroethylene, or stainless steel).
4. Presence of pericardial effusion (moderate or greater), cardiac tamponade, hemodynamically significant left/right shunt, or severe valvular heart disease.
5. Intracardiac thrombus detected by echocardiography within 30 days prior to enrollment.
6. History of acute myocardial infarction, or documented history of hospitalization for Q-wave infarction.
7. History of cerebral infarction, intracerebral hemorrhage, transient ischemic attack (TIA), or reversible ischemic neurologic deficit within the past 6 months, or presence of permanent neurological deficit.
8. Known hemoglobin level below 90 g/L, platelet count below 80×10⁹/L, history of bleeding diathesis or coagulation disorder, or unwillingness to receive blood transfusion.
9. Subjects requiring circulatory support or assisted ventilation.
10. Subjects experiencing cardiac arrest or cardiopulmonary resuscitation (CPR) for more than 5 minutes preoperatively (baseline) or intraoperatively.
11. Subjects unsuitable for femoral or jugular venous access.
12. Known contraindications to cardiac magnetic resonance imaging (CMR), such as claustrophobia, presence of non-CMR compatible foreign bodies or implants, or allergy/intolerance to gadolinium-based contrast agents.
13. Prior coronary artery bypass graft (CABG) surgery.
14. Visible well-developed collateral circulation distal to the target lesion in the target vessel.
15. Current participation in another clinical drug or device study where the primary endpoint has not been reached, or planned participation in another investigational drug or device clinical trial within 12 months after the baseline procedure.
16. Known severe renal disease (estimated glomerular filtration rate (eGFR) <30 mL/(min·1.73m²) as calculated by the MDRD formula*) or undergoing hemodialysis.
17. History of treatment for malignancy within the past 12 months.
18. Subjects with chronic obstructive pulmonary disease (COPD) who are on home oxygen therapy or receiving chronic steroid therapy.
19. Impaired consciousness during PCI, cardiogenic shock (persistent systolic blood pressure ≤90 mmHg despite conservative treatment), or pulmonary edema (peripheral oxygen saturation <90% with rales).
20. Any vascular PCI treatment received within 1 week prior to enrollment.
21. Fibrinolytic therapy received within 24 hours prior to enrollment.
22. -target lesions in vessels other than the left anterior descending artery and its branches requiring treatment during this PCI or within one week thereafter.
23. Known pregnancy or breastfeeding, or female subjects planning pregnancy within 1 year post-procedure and unable to complete follow-up as required.
24. Subjects judged by the investigator to have poor compliance and unable to complete the study as required, or any other reason the investigator deems the subject unsuitable for enrollment.