Triggered activity can be caused by which mechanisms?

Triggered activity can be caused by which mechanisms?

• A. DADs and EADs
• B. Atrioventricular block
• C. Delayed conduction
• D. Ventricular fibrillation

Answer: (A)

Triggered activity happens when afterdepolarizations reach the threshold to fire another action potential. There are two forms: early afterdepolarizations occur during the plateau or repolarization phase of the action potential, and delayed afterdepolarizations occur after repolarization, during diastole. Early afterdepolarizations are promoted when the action potential is prolonged (as in long QT scenarios), often due to reduced repolarizing current or increased inward calcium, and they can initiate ectopic beats or torsades de pointes. Delayed afterdepolarizations come from intracellular calcium overload, with spontaneous calcium release triggering a depolarizing current via the sodium–calcium exchanger, which can also spark extrasystoles. Since triggered activity is driven by these afterdepolarizations, the correct mechanism is DADs and EADs. The other options describe conduction blocks or a rhythm rather than the triggering depolarizations themselves.

Triggered activity happens when afterdepolarizations reach the threshold to fire another action potential. There are two forms: early afterdepolarizations occur during the plateau or repolarization phase of the action potential, and delayed afterdepolarizations occur after repolarization, during diastole. Early afterdepolarizations are promoted when the action potential is prolonged (as in long QT scenarios), often due to reduced repolarizing current or increased inward calcium, and they can initiate ectopic beats or torsades de pointes. Delayed afterdepolarizations come from intracellular calcium overload, with spontaneous calcium release triggering a depolarizing current via the sodium–calcium exchanger, which can also spark extrasystoles. Since triggered activity is driven by these afterdepolarizations, the correct mechanism is DADs and EADs. The other options describe conduction blocks or a rhythm rather than the triggering depolarizations themselves.