The QT interval on ECG can be prolonged in the setting of delayed ventricular repolarization due to congenital ion channel mutation or acquired causes. Prolongation is generally defined as QT interval > 450 milliseconds (ms), although some use different thresholds depending on patient population (eg, 440 ms in men and 460 ms in women). Prolongation carries an increased risk of ventricular arrhythmias, primarily torsades de pointes, resulting in sudden cardiac arrest or recurrent syncope.

• Most patients present with incidental findings on ECG.
• Symptomatic patients will present with ventricular arrythmias with syncope and potentially sudden cardiac death.

QT prolongation can be categorized as congenital or acquired, although there is likely interaction between the two. For example, genetic mutations may predispose certain individuals who are more sensitive to certain stressors.

• Congenital – Genetic condition affecting the channels that regulate the flow of sodium, potassium, and calcium in cardiac cells. At least 10 genes have been identified thus far, with a spectrum of different clinical features, most commonly KCNQ1, KCNH2, and SCN5A. Age of onset is variable, most often occurring in adolescence. It is a leading cause of sudden cardiac death in young adults.
• Acquired – Results from external factors altering sodium, potassium, or calcium currents in cardiac cells, eg, certain medications, cardiac disease, intracranial hemorrhage, electrolyte abnormalities, hypothyroidism, cirrhosis, or hypothermia.