Question

A 60-year-old man with ischemic cardiomyopathy and palpitations is started on amiodarone. Which phase of the cardiac action potential is its primary site of action?

• A. Phase 0 -- Rapid depolarization
• B. Phase 2 -- Plateau
• C. Phase 3 -- Repolarization
• D. Phase 4 -- Resting potential

Hint:

Class III antiarrhythmics like amiodarone act on phase 3 by blocking potassium channels.

Answer 1

The Correct Option is C

Concept: Amiodarone is mainly a Class III antiarrhythmic drug. Class III drugs block potassium channels and prolong repolarization.

Step 1: Identify the drug class.
Amiodarone acts primarily as a: \[ \text{Class III antiarrhythmic} \]

Step 2: Recall Class III action.
Class III drugs block potassium channels and prolong: \[ \text{Action potential duration} \]

Step 3: Identify phase affected.
Potassium efflux is responsible for phase 3 repolarization. Therefore, amiodarone mainly acts on: \[ \text{Phase 3} \] Therefore, the correct answer is Phase 3 -- Repolarization.