Potassium channels repolarisation

EADs interrupt either Phase 2 or 3 repolarisation of the AP. If these afterdepolarisations attain sufficient thresholds, they may produce triggered responses and induce single or multiple extrasystoles and even VT. The EAD is an oscillatory potential that is sensitive to frequency and often occurs at slow stimulation rates. EAD activity has been shown in vitro using many types of isolated cardiac muscle and various cell types including mid-myocardial cells (M-cell) (Antzelevitch 2004). Induction of EAD activity can be induced by a variety of drugs that block sodium and potassium channels as well as by catecholamines. 

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