There is an optimal day on which to perform the CMR scan which allows one to capture the information required to assess the dynamic changes in the reperfused STEMI patient. The main objective is to characterise the dynamic changes in LV function, MI size, myocardial edema, MVO, IMH, interstitial volume in the remote myocardium over the first 10 days of an acute reperfused STEMI in order to identify the optimal day for performing the CMR scan.

This will be a prospective observational study with serial CMR imaging only.

CMR scan Each patient will receive one CMR scan performed on Day 1, Day 3, Day 5, Day 10 following the PPCI procedure on a 3T Philips scanner (see study flow below). All CMR scans will be analysed at a central CMR corelab.

For Day 1, 3, 5, 7 and 10 CMRs, parameters will be collected as follows:

• Left ventricle (LV) ejection fraction and indexed LV end systolic and diastolic volumes and mass using short-axis SSFP cine imaging and myocardial tagging sequences).
• The AAR by T1 and T2 mapping18 as a percentage of the LV over time.
• Signal intensity of T1 and T2 mapping in the MI zone, MI core and remote myocardium over time.
• The incidence of intramyocardial haemorrhage (IMH)(hypo-enhancement on T2* mapping sequence)26.
• The volume of microvascular obstruction (MVO) defined as signal intensity 2 standard deviated below the mean signal intensity of the remote myocardium on the T2* maps.

Additional sequence for Day 3 and 7 CMR scans:

• All the above plus MI size (measured in mass of LGE and expressed as a percentage of the LV mass).

Inclusion Criteria:

1. Confirmed STEMI as per PPCI procedure reports/ clinical notes
2. Proximal to mid coronary artery occlusion.
3. Ability to provide informed consent

Exclusion Criteria:

1. Previous myocardial infarction or coronary artery bypass graft surgery
2. Contraindication for CMR (e.g. ferromagnetic implants, claustrophobia, estimated glomerular filtration rate <30mL/min)

Patients presenting with an acute STEMI