THE MEDICAL LITERATURE Users’ Guides to the Medical Literature XV. How to Use an Article About Disease Probability for Differential Diagnosis

CLINICAL SCENARIO 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. You suspect his anxiety explains his palpitations, that they are mediated by hyperventilation, and are possibly part of a panic attack. While he has no findings of cardiac arrhythmia or hyperthyroidism, you wonder if these disorders are common enough in the emergency department setting to consider seriously. You reject pheochromocytoma as too unlikely. Thus, you can list causes of palpitations, but want more information about the frequency of these causes to choose a diagnostic work-up. You ask the question: “In patients presenting with palpitations, what is the frequency of underlying disorders?”