Which mechanism can trigger tachycardia or other abnormal rhythms such as ectopic beats?

• A. Afterdepolarizations and ischemic injury
• B. Hyperkalemia
• C. Normal sinus rhythm
• D. Heart block

Answer: (A)

The mechanism being tested is afterdepolarizations, which can act as triggers for abnormal rhythms. Afterdepolarizations are unwanted depolarizations that occur either during repolarization (early afterdepolarizations) or after repolarization has begun (delayed afterdepolarizations). Ischemic injury disrupts cellular ion balance, elevates intracellular calcium, and often prolongs the action potential. This combination makes afterdepolarizations more likely. When these abnormal depolarizations reach threshold, they can fire a premature impulse, initiating tachycardia or ectopic beats.

Hyperkalemia changes excitability and conduction but doesn’t primarily generate ectopic triggers via afterdepolarizations; normal sinus rhythm isn’t a trigger for tachyarrhythmias, and heart block tends toward slower, not tachycardic, rhythms.