**Core Concept**
The question is testing understanding of the electrophysiological effects of antiarrhythmic drugs on cardiac action potential. Classifying antiarrhythmic drugs according to their mechanism of action is crucial in this context. The correct answer involves understanding how certain drugs affect the Phase 0 depolarization and action potential duration.

**Why the Correct Answer is Right**
The correct answer is **C. Class IB antiarrhythmic drugs**. Class IB antiarrhythmic drugs, such as lidocaine and phenytoin, decrease the slope of Phase 0 by blocking sodium channels, which reduces the rapid depolarization of the cardiac action potential. Moreover, these drugs also prolong the action potential duration by reducing the rate of repolarization. This is achieved by blocking potassium channels, particularly the rapidly activating potassium channels (IKr).

**Why Each Wrong Option is Incorrect**
**Option A:** Class Ia antiarrhythmic drugs (e.g., quinidine) primarily prolong the action potential duration by blocking potassium channels but may not significantly decrease the slope of Phase 0.
**Option B:** Class III antiarrhythmic drugs (e.g., amiodarone) primarily prolong the action potential duration by blocking potassium channels but do not significantly decrease the slope of Phase 0.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that Class IB antiarrhythmic drugs are primarily used for acute management of ventricular arrhythmias due to their rapid onset and short duration of action.

**Correct Answer:** C. Class IB antiarrhythmic drugs.