What is delayed Afterdepolarization?
Delayed afterdepolarizations (DADs) are transient depolarizations in the diastolic phase following an action potential (AP) that have been linked to arrhythmogenesis in cardiac diseases 1-3.
What are early and delayed Afterdepolarization?
Afterdepolarizations can be either early or delayed. Early afterdepolarizations occur during late phase 2 or phase 3 and can lead to a salvo of several rapid action potentials or a prolonged series of action potentials.
What causes early after depolarization?
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.
What causes repolarization of the heart?
Repolarization (phase 3 of the action potential) occurs because of an increase in potassium permeability. At the SA node, potassium permeability can be further enhanced by vagal stimulation. This has the effect of hyperpolarizing the cell and reducing the rate of firing.
What is EAD and dad?
EADs are abnormal depolarizing oscillations of membrane potential that occur during the plateau or late repolarization of an action potential, while DADs are depolarizing membrane potential oscillations initiated after full repolarization of the triggering action potential (Figure 1).
What is early Afterdepolarization?
Early afterdepolarizations (EADs) are spontaneous depolarizations during the repolarization phase of an action potential in cardiac myocytes. It is widely known that EADs are promoted by increasing inward currents and/or decreasing outward currents, a condition called reduced repolarization reserve.
Why do EADs occur?
EADs occur in the setting of reduced repolarization reserve, which can result from a reduction in outward current, an increase in inward current, or both, such that the net outward current required to repolarize the myocyte is compromised.
What happens if repolarization does not occur?
The lack of repolarization means that neuron stays at a high voltage, which slows sodium channel deinactivation to a point where there is not enough inwards Na+ current to depolarize and sustain firing.
What does prolonged repolarization mean?
Repolarization in the heart is largely due to efflux of potassium out of the cells. When potassium channels are blocked, as with the class IA antiarrhythmics, repolarization is prolonged. Prolongation of repolarization is reflected by prolonged QT on the ECG.
What is re entry phenomenon?
Re-entry ventricular arrhythmia is a type of paroxysmal tachycardia occurring in the ventricle where the cause of the arrhythmia is due to the electric signal not completing the normal circuit, but rather an alternative circuit looping back upon itself. There develops a self-perpetuating rapid and abnormal activation.
What is a delayed afterdepolarization?
Delayed afterdepolarizations. Cellular mechanisms of early afterdepolarizations (EADs) and delayed afterdepolarizations (DADs). Delayed afterdepolarizations (DADs) begin during phase 4, after repolarization is completed but before another action potential would normally occur via the normal conduction systems of the heart.
Do delayed afterdepolarizations generate a substrate vulnerability to arrhythmia triggers?
Abstract Background: Delayed afterdepolarizations (DADs) have been well characterized as arrhythmia triggers, but their role in generating a tissue substrate vulnerable to reentry is not well understood.
How can action potentials be generated during afterdepolarization?
If the afterdepolarization is of sufficient amplitude to engage the rapid sodium channels, another action potential can be generated. Triggered activity, like re-entry, can be induced by premature beats or by pacing techniques.
What is afterdepolarization of myocytes?
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 .