Lack of financial support for recruitment and follow-up activities.

In this study we pretend to determine the molecular (miRNAs expression, angiogenic and inflammatory biomarkers) and microcirculatory (assessed by the innovative continuous intracoronary thermodilution technique) effects of PiCSO compared to a standard PCI control group in patients with high-risk anterior STEMI. Then, we aim to assess the efficacy of these molecular biomarkers as prognostic tools. Also, we will evaluate the impact of PiCSO on the coronary microcirculation beyond the acute phase in the follow-up six months after STEMI. Finally, we will assess PiCSO influence on Heart Failure (HF) clinical variables and patients' quality of life including a cost-effectiveness assessment in the mid-term follow-up one year after the STEMI event.

Inclusion Criteria:

1. Age ≥ 18 years old.
2. Anterior STEMI (ECG with persistent elevation ≥ 2 mm (0.2 mV) in 2 or more contiguous anterior precordial leads (V2, V3, V4) in men or ≥ 1.5 mm (0.15 mV) in women.
3. Culprit lesion in proximal or mid Left Anterior Descending Artery (LAD).
4. Pre-PCI TIMI flow 0-1.
5. Symptoms consistent with myocardial ischemia (persistent chest pain, dyspnea, nauseas/vomiting, fatigue, palpitations or syncope) present for ≤ 12 hours.
6. The patient is eligible for primary PCI.
7. Informed consent received and signed for study enrollment.

Exclusion Criteria:

1. Contraindication to coronary angiogram or PCI.
2. Implants or foreign bodies in the coronary sinus.
3. Known allergies to polyurethanes, Polyethylene Terephthalate (PET) or stainless steel.
4. Known pregnancy or breastfeeding.
5. Known coagulopathy.
6. Known severe kidney disease (eGFR <=30 mL/min/1.73) and/or hemodialysis.
7. Known large pericardial effusion or cardiac tamponade.
8. Central hemodynamically relevant left-right shunt.
9. Previous MI or Coronary Artery Bypass Graft (CABG).
10. Previous history of stroke, transient ischemic attack (TIA) or reversible ischemic neurological deficit within last 6 months.
11. Cardiopulmonary resuscitated (CPR) cardiac arrest ≥ 5 minutes whom baseline neurologic status is not present.
12. Unconscious at presentation.
13. Need for circulatory support.
14. Need for invasive mechanical ventilation.
15. Need for temporal intravenous pacemaker.
16. Patient not suitable for femoral access.
17. Known contraindication for adenosine administration (severe asthma, complicated Atrioventricular (AV) block, critical aortic stenosis, severe cardiac arrhythmias, severe valve diseases).
18. Known epicardial stenosis greater than 50% distal to the culprit LAD lesion.
19. Active participation in another drug or device investigational trial.
20. Medical, social or psychological condition that limits the ability of patient to participate in the study.
21. Patients with definite or probable coronavirus disease 19 diagnosis within 2 weeks prior to STEMI.

The subjects as well as the investigator performing the procedure will not be blind to the study treatment. An independent experienced cardiologist, who will be blinded to all clinical data; will analyze anonymized Cardiac Magnetic Resonance (CMR) images for unbiased endpoints assessment.