**Core Concept**
Verapamil is a calcium channel blocker that is effective in controlling the ventricular rate in patients with supraventricular tachycardia (PSVT) by blocking the AV node. This results in a decrease in the heart rate, thereby alleviating symptoms.

**Why the Correct Answer is Right**
Verapamil works by inhibiting the L-type calcium channels in the cardiac muscle, particularly in the AV node. This action reduces the influx of calcium ions into the cardiac muscle cells, leading to a decrease in the contractility of the heart and a consequent decrease in heart rate. In the context of PSVT, verapamil helps to control the ventricular rate by blocking the AV node, thereby preventing the rapid transmission of electrical impulses from the atria to the ventricles.

**Why Each Wrong Option is Incorrect**
**Option A:** Amiodarone is an antiarrhythmic medication that is effective in treating various types of arrhythmias, including PSVT. However, it is not typically used as a first-line treatment for maintenance therapy in PSVT due to its potential side effects and interactions.
**Option B:** Lignocaine is an antiarrhythmic medication that is effective in treating ventricular arrhythmias. However, it is not typically used to control the ventricular rate in PSVT, as it can actually worsen the condition by increasing the heart rate.
**Option D:** Adenosine is a medication that is effective in terminating PSVT by transiently blocking the AV node. However, it is not typically used for maintenance therapy, as it has a short duration of action and requires repeated administration.

**Clinical Pearl / High-Yield Fact**
When treating PSVT, it's essential to differentiate between narrow-complex and wide-complex tachycardias. Narrow-complex tachycardias are typically caused by AV nodal reentry, and verapamil is an effective treatment option. In contrast, wide-complex tachycardias often require more urgent treatment, such as electrical cardioversion.

**✓ Correct Answer: C. Verapamil**