afterdepolarization

Afterdepolarization refers to abnormal electrical activity in cardiac cells that occurs after the repolarization phase of an action potential. It is a phenomenon that can lead to triggered arrhythmias. Afterdepolarizations are broadly categorized into early afterdepolarizations (EADs) and delayed afterdepolarizations (DADs).

Early afterdepolarizations occur during or shortly after repolarization, when the membrane potential is still negative but not yet fully restored to its resting potential. They are often associated with prolonged action potentials and can be triggered by conditions that prolong the repolarization period, such as certain medications or electrolyte imbalances. EADs are thought to be caused by a transient influx of calcium into the cell, which can re-excite the cell and initiate a new action potential.

Delayed afterdepolarizations occur after the cardiac cell has fully repolarized and returned to its resting membrane potential. They are often observed in conditions of intracellular calcium overload, which can occur during states of sympathetic stimulation or ischemia. DADs are believed to arise from the spontaneous release of calcium from the sarcoplasmic reticulum, leading to a subsequent influx of sodium and calcium ions, which depolarizes the cell membrane and can trigger a new action potential. Both EADs and DADs can initiate premature beats and contribute to the development of serious ventricular arrhythmias like torsades de pointes and ventricular tachycardia.