Early afterdepolarizations occur in situations in which phase 2 (the plateau ), or phase 3. (rapid repolarization) is prolonged and the QT interval on the ECG is lengthened. As discussed in Chapter 5, the plateau phase and phase 3 of the action potential may be prolonged by bradycardia, by abnormalities in the genes encoded for the ionic channels that regulate the poassium or sodium channels and by a variety of drugs and other agents which interfere with the ionic currents responsible for repolarization.. These include but are not limited to the class 1a and class 3 antiarrhythmic drugs. Early afterdepolariztions are one cause of the type of ventricular tachycardia referred to as “Torsade de Pointes”.