A n active, physically fit, and previously healthy 23-year-old man is referred by his family physician to a cardiology clinic with a several-month history of progressively worsening episodes of palpitations associated with dyspnea. He reports experiencing brief episodes almost hourly and describes the palpitations as being extremely rapid and the rhythm as regular.Dr Salehian: Palpitations as a chief complaint are a common issue routinely assessed by family physicians, general internists, emergency department physicians, and cardiologists. The differential diagnosis in such patients is broad and often not related to a primary cardiac issue or arrhythmia. Broadly, symptoms of palpitations may be related to cardiac arrhythmia or structural heart disease, medications, recreational drugs and alcohol, metabolic disorders, high output states, or psychiatric conditions. To help to determine the etiology of the patient's symptoms, a thorough history, physical examination, and basic laboratory investigations are necessary to help to determine which further investigations are required.The patient reports mild dyspnea with the episodes but denies associated syncope or presyncope, chest discomfort, nausea, or vomiting. The palpitations are not precipitated by exertion, and there are no other identifiable aggravating factors. He is unaware of any physical activity limitations, exertional symptoms, or features suggestive of congestive heart failure. There is no drug or alcohol use and absence of a family history of early coronary artery disease, congenital heart disease, dysrhythmia, or sudden cardiac death. He also denies recent infectious symptoms. On physical examination, he is afebrile, with a blood pressure of 116/72 mm Hg, heart rate of 68 bpm, and respiratory rate of 14 breaths per minute. There is no adenopathy noted, and the jugular venous pressure is not elevated. Carotid upstroke is normal without any bruits. On cardiac examination, apical impulse is not easily palpable, and no obvious heaves or thrills are felt. On auscultation, first and second heart sounds are normal, with no extra heart sounds, murmurs, or rubs. Lungs are clear to auscultation with no adventitious sounds. Abdomen is soft, and organomegaly is not detected. Peripheral pulses are all normal. There is no peripheral edema detected in his extremities. All blood work, including complete blood count, electrolytes, and thyroid function studies, is within normal limits.Dr Salehian: In this patient, there are no significant worrisome features in the history or physical examination to suggest a sinister arrhythmia as the cause of his symptoms. Basic blood work is reassuringly normal as well. Although not completely ruled out by a benign history, absence of certain features is encouraging. For example, symptoms are not precipitated by exercise (catecholaminergic polymorphic ventricular tachycardia [VT], hypertrophic obstructive cardiomyopathy), and there is no history suggestive of underlying cardiomyopathy (nonischemic or ischemic cardiomyopathy) and no fa...