Revascularization strategies for ST elevation myocardial infarction (STEMI) study (ASSIST-CMR) will compare the effects of two revascularization strategies [same sitting multivessel primary PCI (SS-PCI) and culprit vessel only primary PCI (IRA-PCI)] on myocardial infarct size (MIS) as determined by cardiac magnetic resonance (CMR) imaging in patients presenting with STEMI and multivessel disease (MVD).

Inclusion Criteria:

• High risk ST elevation myocardial infarction evidenced by: ≥2 mm ST elevation in 2 anterior or lateral leads; or ≥2 mm ST elevation in 2 inferior coupled with ST depression in 2 contiguous anterior leads for a total ST deviation of ≥8 mm; or New left bundle branch block with at least 1 mm concordant ST elevation.
• Multivessel CAD as evidenced by ≥1 significant (≥70% by visual assessment or FFR<0.80 for 50-70% stenosis) stenosis in non-IRA.
• Successful IRA-PCI with <10% residual angiographic stenosis and TIMI III flow.
• Written informed consent.

Exclusion Criteria:

• Age ≤ 18 years.
• Prior coronary artery bypass graft (CABG) surgery.
• Administration of thrombolytic therapy.
• Non-IRA stenosis is a chronic total occlusion or located in left main artery.
• Hemodynamic instability evidenced by BP<90 mmHg, Killip class ≥2, need for inotropes/vasopressors.
• Known renal insufficiency (estimated GFR < 50ml/min).
• Contraindication to CMR.