Gene mutations that are associated with abnormalities in cardiac repolarization lead to prolongation of the QT interval on the electrocardiogram, also known as congenital long QT syndrome. Patients with congenital long QT syndrome are at increased risk of ventricular arrhythmias and sudden death.

Acquired long QT syndrome is a cardiac repolarization disorder characterized by acquired QT interval prolongation on the electrocardiogram. This is often caused by drug and electrolyte abnormalities that can trigger torsades de pointes ventricular arrhythmias.