What mechanism causes triggered arrhythmias?

What mechanism causes triggered arrhythmias?

• A. Afterdepolarization
• B. Reentry
• C. Automaticity
• D. Conduction block

Answer: (A)

Triggered arrhythmias come from afterdepolarizations that push the cell to threshold and fire an extra impulse. These afterdepolarizations occur either during repolarization (early afterdepolarizations) when the action potential is prolonged, or after full repolarization (delayed afterdepolarizations) often due to calcium overload or catecholamine effects. In both cases, the premature impulse is generated by a depolarizing event tied to the cell's delayed return to resting potential, rather than by a sustained reentrant circuit or by spontaneous automatic pacing. Reentry relies on a circulating wavefront and a balance of conduction and refractoriness, which explains many tachyarrhythmias but not the sudden depolarizing trigger from a single cell. Automaticity refers to cells that spontaneously depolarize to reach threshold without a triggering afterdepolarization. Conduction block can contribute to reentry or bradyarrhythmias by altering pathways, but it does not by itself create the depolarizing trigger responsible for triggered activity.

Triggered arrhythmias come from afterdepolarizations that push the cell to threshold and fire an extra impulse. These afterdepolarizations occur either during repolarization (early afterdepolarizations) when the action potential is prolonged, or after full repolarization (delayed afterdepolarizations) often due to calcium overload or catecholamine effects. In both cases, the premature impulse is generated by a depolarizing event tied to the cell's delayed return to resting potential, rather than by a sustained reentrant circuit or by spontaneous automatic pacing.

Reentry relies on a circulating wavefront and a balance of conduction and refractoriness, which explains many tachyarrhythmias but not the sudden depolarizing trigger from a single cell. Automaticity refers to cells that spontaneously depolarize to reach threshold without a triggering afterdepolarization. Conduction block can contribute to reentry or bradyarrhythmias by altering pathways, but it does not by itself create the depolarizing trigger responsible for triggered activity.