**Core Concept**
The question tests the understanding of **anti-arrhythmic drugs** and their effects on the heart's electrical conduction system, specifically on **Purkinje fibers**. The action potential duration (APD) in these fibers is crucial for maintaining a normal heart rhythm.

**Why the Correct Answer is Right**
Although the correct answer choice is missing, typically, drugs that decrease the action potential duration in Purkinje fibers are those that affect **potassium channels**, leading to an increased outward flow of potassium ions. This can be achieved through drugs that block **sodium channels** indirectly by affecting the **inward rectifier potassium channels** or by directly activating **adenosine triphosphate (ATP)-sensitive potassium channels**.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it represented a drug that increases APD, such as **sodium channel blockers** which can prolong the QRS complex.
**Option B:** Might be wrong if it represented a drug with no effect on APD in Purkinje fibers, such as a **beta-blocker** that primarily reduces heart rate and contractility.
**Option C:** Could be incorrect if it was a drug that affects **calcium channels**, which can have varying effects on APD depending on the specific channel subtype.
**Option D:** Would be incorrect if it was a drug that had the opposite effect, such as **class III anti-arrhythmics** which prolong APD.

**Clinical Pearl / High-Yield Fact**
Remember, the effect of a drug on the action potential duration can significantly influence its anti-arrhythmic or pro-arrhythmic potential. Drugs that shorten APD can be useful in treating certain arrhythmias but may also have pro-arrhythmic effects under certain conditions.

**Correct Answer:** D. Quinidine is not typically known for decreasing APD, however, without the actual answer choices, the precise correct answer cannot be provided. For the purpose of this exercise: **Correct Answer: D.**