A 68-year-old man presents to the emergency department with 2 hours of crushing retrosternal chest pain radiating to his left arm and jaw, associated with diaphoresis and nausea. He has a history of hypertension and dyslipidaemia. ECG shows 3 mm ST-segment elevation in leads II, III and aVF with reciprocal ST depression in I and aVL. What is the most appropriate immediate management step?