## **Core Concept**
The question pertains to the management of Paroxysmal Supraventricular Tachycardia (PSVT), a condition characterized by episodic tachycardia originating above the ventricles. The treatment often involves acute termination of the episode and long-term maintenance to prevent recurrence. Various anti-arrhythmic drugs can be used, classified under the Vaughan-Williams classification.

## **Why the Correct Answer is Right**
The correct answer, , is a calcium channel blocker. Calcium channel blockers, particularly non-dihydropyridines like verapamil and diltiazem, are effective in treating PSVT. They work by blocking the L-type calcium channels in the atrioventricular (AV) node, which reduces AV nodal conduction velocity and refractoriness, thereby interrupting the reentrant circuits that sustain PSVT. Verapamil is specifically used for long-term management due to its oral bioavailability and efficacy in preventing recurrence.

## **Why Each Wrong Option is Incorrect**
- **Option A:** is incorrect because, while it can be used for certain types of arrhythmias, it is not the first choice for maintenance in PSVT.
- **Option B:** is incorrect because it is more commonly used for atrial fibrillation and not typically for PSVT maintenance.
- **Option D:** is incorrect because, although it can be used in some supraventricular tachycardias, it is not the preferred agent for long-term management of PSVT.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that for PSVT, **verapamil (a calcium channel blocker)** is often considered a drug of choice for long-term prevention of episodes, especially in patients without significant heart failure or severe hypotension. Another important consideration is that beta-blockers can also be effective but might not be as potent as calcium channel blockers in certain cases.

## **Correct Answer:** . Verapamil