Long QT syndrome

#### Case scenario A 19 year old female student consulted her general practitioner about two recent episodes of syncope, both of which occurred while playing hockey. Her team mates reported that she collapsed suddenly with little warning, recovering rapidly within 30 seconds without confusion. She was otherwise well, although she was taking erythromycin for an infected leg abrasion at the time of the events. As part of the routine evaluation for syncope, her general practitioner performed a 12 lead electrocardiogram, which showed a prolonged corrected QT interval of 510 ms. Congenital long QT syndrome is a potential cause of avoidable sudden cardiac death. Affected individuals may have ventricular arrhythmias, leading to palpitations, syncope, and, if sustained, cardiac arrest.1 The syndrome is inherited in an autosomal dominant fashion, with variable disease expression: those severely affected may die in fetal or neonatal life, but others remain asymptomatic throughout their life. At a cellular level, genetically encoded abnormalities in sodium and potassium ion channels within the cell membrane lengthen cardiac repolarisation, which manifests as a prolongation of the QT interval in the electrocardiogram. QT prolongation may be acquired secondary to certain medications, metabolic disturbance, cerebral injury, myocardial disease, and hypothermia—factors that may also unmask the congenital syndrome in a previously asymptomatic individual. #### How common is long QT syndrome? Syncope is highly prevalent in young adults. Among 394 students, 154 reported at least one episode of syncope.4 In a young, fit adult (such as outlined in the scenario box), important differential diagnoses include the most common and benign cause of …