The overall objective of this research proposal is to use OCT to investigate those morphological culprit plaque characteristics associated with the risk of developing MVO in reperfused STEMI patients.

The specific research objectives include:

1. To use OCT to determine the type of plaque (plaque rupture, plaque erosion or calcified nodule) most associated with the presence and severity of MVO (as measured by IMR and cardiac MRI).
2. To use OCT to investigate the relationship between the extent of tissue protrusion and the amount of residual stent thrombus with the presence and severity of MVO (as measured by IMR and cardiac MRI).

Inclusion Criteria:

1. Confirmed STEMI as per the in-charge consultant based on presenting history, ECG and angiogram findings.
2. < 12 hours of onset of chest pain.
3. Ability to provide informed consent

Exclusion Criteria:

1. Previous myocardial infarction or coronary artery bypass graft surgery
2. Cardiac arrest or cardiogenic shock
3. Inability to advance the OCT catheter or to obtain good image quality
4. Ostial lesions
5. Significant renal impairment
6. Contraindications for cardiac MRI
7. Contraindication for adenosine (for IMR measurement)

The patients presenting with a STEMI and undergoing PPCI will be screened and approached to participate in this study.