The causes of the electrocardiographic features referred to as early repolarization are not well understood. It is thought that there are voltage gradients created during the early part of the action potential plateau that are the result of differences in action potential configuration and duration in the epicardial. middle and endocardial regions of the ventricular wall. The presence of a transient outward current, referred to as Ito, leading to a notch following the action potential spike in epicardial, but not in mid-myocardial and endocardial cells may contribute to these voltage differences.