Electrocardiographic implications of the prolonged QT interval.

The QT interval measures the time from the start of the QRS complex to the end of the T wave. Prolongation of the QT interval may lead to malignant ventricular tachydysrhythmias, including torsades de pointes. Causes of QT prolongation include congenital abnormalities of the sodium or potassium channel, electrolyte abnormalities, and medications; idiopathic causes have also been identified. Patients can be asymptomatic or present with syncope, palpitations, seizure-like activity, or sudden cardiac death. Management involves looking for and treating reversible causes. For patients with congenital or idiopathic QT interval prolongation, the use of beta-blockers can be considered. Certain subsets of patients benefit from implantation of a cardioverter-defibrillator. Clinicians must remain vigilant for QT interval prolongation when interpreting electrocardiograms, especially in patients presenting with syncope or ventricular arrhythmias.