The QT interval represents the time between the onset of ventricular depolarization and the end of ventricular repolarization. It reflects the total time the ventricles take to de- and repolarize.

The QT interval represents the time between the onset of ventricular depolarization and the end of ventricular repolarization. It reflects the total time the ventricles take to de- and repolarize. Abnormalities in the QT interval can cause serious arrhythmias and sudden cardiac death. QT prolongation can precipitate torsades de pointes, a specific form of polymorphic ventricular tachycardia characterized by irregular (polymorphic) QRS complexes that appear to twist around the isoelectric baseline. The risk of ventricular fibrillation is very high during torsade de pointes.