Acute Pericarditis Diffuse ST Elevation PR Depression

A 32-year-old man presents to the emergency department with 3 days of sharp, retrosternal chest pain that worsens with inspiration and when lying supine, but improves when sitting forward. On examination, a high-pitched triphasic scratching sound is heard at the left lower sternal border. A 12-lead ECG is obtained and shows the pattern marked **A** in the diagram. Which of the following is the MOST appropriate initial management for this patient?

A 26-year-old man presents with 24 hours of sharp, retrosternal chest pain worse on inspiration and lying flat, partially relieved by sitting forward. He had a flu-like illness 10 days ago. Examination reveals a pericardial friction rub and mild troponin elevation (0.14). A 12-lead ECG is performed. The structure marked **A** in the diagram—diffuse concave-upward ST-segment elevation in inferior/lateral leads—is a hallmark of acute pericarditis. Which of the following findings would BEST distinguish this ECG pattern from acute myocardial infarction (STEMI)?