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Long Qt Syndrome 1

Long QT syndrome


Vignette: A 25-year-old woman comes to the physician because of palpitations and lightheadedness. She reports that these symptoms have been occurring frequently over the past six months. Her blood pressure is 90/60 mm Hg and pulse is 95/min. An EKG shows a prolonged QT interval. Which of the following is the most likely cause of this patient's symptoms?


A) Dysfunction of the sodium channels

B) Dysfunction of the potassium channels

C) Dysfunction of the calcium channels

D) Increased sympathetic activity

E) Decreased parasympathetic activity


B) Dysfunction of the potassium channels


This patient's symptoms of palpitations and lightheadedness, along with the EKG findings of a prolonged QT interval, suggest a diagnosis of Long QT Syndrome (LQTS). LQTS is a disorder of myocardial repolarization characterized by a prolonged QT interval on EKG (>440 ms in men, >460 ms in women). Many cases of LQTS are due to genetic mutations affecting cardiac ion channels, most commonly the potassium channels. Dysfunction of these channels leads to prolonged repolarization and a propensity for ventricular arrhythmias, which can result in syncope and sudden cardiac death. Symptoms most frequently occur during exercise or stress, which increase heart rate and shorten the action potential duration, further exacerbating the repolarization defect.


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