Which antiarrhythmic class is associated with positive inotropy and helps prevent reentrant arrhythmias by blocking potassium channels?

• A. Sodium Channel Blockers
• B. Beta Blockers
• C. Potassium Channel Blockers
• D. Calcium Channel Blockers

Answer: (C)

Blocking potassium channels slows repolarization, which lengthens the cardiac action potential and increases the refractory period. That extended refractoriness makes it harder for a reentrant impulse to re-enter and propagate, so reentrant arrhythmias are prevented. This is the defining effect of Class III antiarrhythmics, the potassium channel blockers. While some agents in this class can have other actions that influence contractility, the arrhythmia suppression relevant here comes from the prolonged repolarization and increased refractoriness. In contrast, sodium channel blockers mainly slow depolarization and conduction, beta blockers reduce sympathetic drive and can depress contractility, and calcium channel blockers slow AV nodal conduction. So the potassium channel blockers are the ones most linked to preventing reentry via extended refractoriness.