第116回 E問題 38

A 21-year-old previously healthy man presented to the emergency room with chest pain, which was worse on breathing, lasting for two days.

Lung and heart examinations were unremarkable. Chest X-ray（別冊No. 3Ａ）and ECG（別冊No. 3Ｂ）are shown in the figure.

What is the most likely diagnosis?