MCQ – 101224

Amiodarone primarily acts by inhibiting which phase of the cardiac action potential?

Correct Answer � D Explanation

– Phase 3 of the cardiac action potential involves the repolarization phase, marked by potassium efflux.
– Amiodarone, a Class III antiarrhythmic, blocks potassium channels, thereby:
– Inhibiting Phase 3
– Prolonging repolarization
– ↑ action potential duration & refractory period

Mechanism:

– Phase 0: Na⁺ influx; Class I drugs (e.g., lidocaine)
– Phase 1: Transient K⁺ efflux; rarely targeted
– Phase 2: Ca²⁺ influx; Class IV drugs (e.g., verapamil)
– Phase 3: K⁺ efflux; Class III drugs (e.g., amiodarone)
– Phase 4: Resting potential; maintained by Na⁺/K⁺ ATPase