You are an experienced clinician working at a hospital emergency
department. One morning, a 33-year-old man presents with palpitations.
He describes the new onset of episodes of fast, regular chest pounding,
which come on gradually, last 1 to 2 minutes, and occur several times a
day. He reports no relation of symptoms to activities and no change in
exercise tolerance. He is very anxious and tells you he fears heart
disease. He has no other symptoms, no personal or family history of
heart disease, and takes no medications. His heart rate is 90 bpm and
regular, and physical examination of his eyes, thyroid gland, lungs,
and heart is normal. His 12-lead electrocardiogram is normal, without
arrhythmia or signs of pre-excitation.