Everything about Afterdepolarization totally explained
Afterdepolarizations are abnormal
depolarizations of
cardiac myocytes that interrupt phase 2, phase 3, or phase 4 of the
cardiac action potential in the
electrical conduction system of the heart. Afterdepolarizations may lead to
cardiac arrhythmias.
Early afterdepolarizations
Early afterdepolarizations (EADs) occur with abnormal depolarization during phase 2 or phase 3, and are caused by an increase in the frequency of abortive
action potentials before normal repolarization is completed. Phase 2 may be interrupted due to augmented opening of
calcium channels, while phase 3 interruptions are due to the opening of
sodium channels. Early afterdepolarizations can result in
torsades de pointes,
tachycardia, and other
arrhythmias..
Afterhyperpolarisations can also occur in cortical pyramidal neurons. There, they typically follow an action potential and are mediated by voltage gated sodium or chloride channels. This phenomenon requires potassium channels to close quickly to limit repolarisation. It is responisible for the difference between regular spiking and intrinsically bursting pyramidal neurons.
Delayed afterdepolarizations
Delayed afterdepolarizations (DADs), on the other hand, begin during phase 4 - after repolarization is completed, but before another action potential would normally occur. They are due to elevated cytosolic
calcium concentrations, as might be seen with
digoxin toxicity.
Further Information
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