The aim of the Danish Organization for Randomized Trials with Clinical Outcome (SORT OUT) IX STEMI OCT is to compare early vascular healing of the polymer-free Biolimus-eluting BIOFREEDOM stent with a biodegradable-polymer Sirolimus-eluting ORSIRO stent in patients with ST-segment elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PCI).

SORT OUT IX STEMI OCT is a randomized 1:1 study comparing the polymer-free Biolimus-eluting BIOFREEDOM stent with a biodegradable-polymer Sirolimus-eluting ORSIRO stent patients with STEMI treated with primary PCI.

Vascular healing index (uncovered stent struts, malapposed stent struts, maximal intima coverage and accumulated extra-stent lumen volume) assessed with optical coherence tomography (OCT) 1 month after primary PCI.

Patients will be enrolled by the investigators and randomly allocated to treatment groups after diagnostic coronary angiography and before primary PCI. A web based Trial Partner randomization system will be used.

OCT will be performed with the frequency-domain OPTIS OCT system and Dragonfly™ Imaging Catheter during the index procedure and after 1 months.

Inclusion Criteria:

• Patients aged 18 years or over with STEMI, requiring treatment with a drug-eluting stent.

Exclusion Criteria:

• life expectancy of less than one year; an allergy to aspirin, clopidogrel, ticagrelor, prasugral, biolimus or sirolimus; participation in another randomized trial; chronic renal disease; or inability to provide written informed consent.