Which are the two types of afterdepolarizations?

Which are the two types of afterdepolarizations?

• A. SA And AV
• B. EADs And DADs
• C. P Waves And T Waves
• D. Atrial And Ventricular

Answer: (B)

Afterdepolarizations are abnormal depolarizations that occur around or after an action potential and can trigger arrhythmias. There are two distinct forms: Early afterdepolarizations occur during the repolarization phase of the cardiac action potential, typically in the plateau or repolarization phases (phases 2–3). They are favored when the action potential is prolonged, such as with QT prolongation, bradycardia, or drugs that slow repolarization. Mechanistically, they arise from reactivation of inward currents (notably L-type calcium channels) or reduced outward repolarizing currents, causing a secondary bump in voltage before full repolarization completes. Delayed afterdepolarizations occur after the cell has fully repolarized (diastole). They are usually driven by intracellular calcium overload, which leads to spontaneous calcium release from the sarcoplasmic reticulum. This triggers an inward current via the sodium–calcium exchanger, producing a transient depolarization that can provoke ectopic beats. So the two types are early afterdepolarizations and delayed afterdepolarizations. They differ in timing relative to the action potential and in their underlying triggers—prolonged repolarization for EADs, and calcium overload with diastolic depolarization for DADs.

Afterdepolarizations are abnormal depolarizations that occur around or after an action potential and can trigger arrhythmias. There are two distinct forms:

Early afterdepolarizations occur during the repolarization phase of the cardiac action potential, typically in the plateau or repolarization phases (phases 2–3). They are favored when the action potential is prolonged, such as with QT prolongation, bradycardia, or drugs that slow repolarization. Mechanistically, they arise from reactivation of inward currents (notably L-type calcium channels) or reduced outward repolarizing currents, causing a secondary bump in voltage before full repolarization completes.

Delayed afterdepolarizations occur after the cell has fully repolarized (diastole). They are usually driven by intracellular calcium overload, which leads to spontaneous calcium release from the sarcoplasmic reticulum. This triggers an inward current via the sodium–calcium exchanger, producing a transient depolarization that can provoke ectopic beats.

So the two types are early afterdepolarizations and delayed afterdepolarizations. They differ in timing relative to the action potential and in their underlying triggers—prolonged repolarization for EADs, and calcium overload with diastolic depolarization for DADs.