Which mechanism of arrhythmia is associated with early afterdepolarizations (EAD) and delayed afterdepolarizations (DAD)?

• A. Triggered activity
• B. Abnormal automaticity
• C. Reentry
• D. Blockade of conduction

Answer: (A)

Triggered activity is the mechanism behind arrhythmias caused by afterdepolarizations that reach threshold and fire extra impulses. Early afterdepolarizations occur during the action potential’s plateau or early repolarization and are often linked to prolonged repolarization (long QT scenarios), which allows a depolarizing current to re-ex cite and trigger another beat. Delayed afterdepolarizations happen after full repolarization, typically due to calcium overload that prompts spontaneous calcium release and activation of the sodium–calcium exchanger, generating a depolarizing current that can initiate a new impulse. So both EADs and DADs fit under triggered activity. Abnormal automaticity is spontaneous pacemaker-like firing from non-pacemaker tissue without afterdepolarizations, reentry involves a circulating wavefront, and conduction block refers to impaired impulse propagation rather than afterdepolarizations triggering beats.