A progressively changing ECG

A woman in her 70s was admitted to the emergency department for non-radiating retrosternal dull chest pain, which started two hours after an argument. Her medical history included hypertension, hyperlipidaemia, type 2 diabetes, and no history of coronary artery disease. She was haemodynamically stable on arrival: blood pressure 105/65 mm Hg, heart rate 74 beats/min, and respiratory examination was unremarkable in outcome. A 12-lead electrocardiogram (ECG) showed sinus rhythm with non-specific ST-segment changes (fig 1). Troponin I was mildly elevated (0.618 ng/mL, normal range 0–0.1 ng/mL); N-terminal prohormone brain natriuretic peptide (NT-proBNP) was 359 pg/mL (0–100 pg/mL); serum potassium was 4.0 mmol/L (3.5–5.5 mmol/L); and serum magnesium was 0.91 mmol/L (0.75–1.04 mmol/L). She was admitted to the coronary care unit for haemodynamic monitoring. Six hours later, when the chest pain subsided, the …