Another form of spontaneous activity is referred to as “triggered activity”. This term is used to describe automatic activity arising from, or triggered by, a prior action potential. These spontaneously occurring action potentials are also referred to as after-depolarizations. When, as illustrated in the upper panel of this figure, an after-depolarization arises during the plateau phase of the action potential (phase 2) or the phase of rapid repolarization (phase 3),it is referred to as an early after-depolarization (EAD). When, as in the lower panel, it occurs after repolarization is completed, i.e. during phase 4 of the action potential, it referred to as a delayed after-depolarization (DAD).