**Core Concept**
Supraventricular tachycardia (SVT) is a type of abnormal heart rhythm originating from the atria or the atrioventricular (AV) node, characterized by a rapid heart rate. The goal of treatment is to restore a normal sinus rhythm and control the heart rate.

**Why the Correct Answer is Right**
The drug of choice for controlling SVT is **Adenosine**. Adenosine acts by transiently blocking AV nodal conduction, thereby interrupting the re-entrant circuit that maintains the arrhythmia. Adenosine has a very short half-life, which allows for a quick response without causing prolonged AV block. It is administered intravenously in a bolus dose of 6 mg, with a rapid push, and can be repeated if necessary.

**Why Each Wrong Option is Incorrect**
**Option A:** **Digoxin** is not the first-line treatment for SVT. Although digoxin can help control ventricular rate in atrial fibrillation, it is not effective in converting SVT to a normal rhythm.

**Option B:** **Lidocaine** is primarily used to treat ventricular arrhythmias, such as ventricular tachycardia. It is not effective in controlling SVT.

**Option C:** **Verapamil** is a calcium channel blocker that can be used to control SVT, but it is not the first-line treatment. Verapamil can be used if adenosine is ineffective or contraindicated.

**Clinical Pearl / High-Yield Fact**
Remember that adenosine's effect is transient and reversible, so it is essential to monitor the patient's response and repeat the dose as needed to maintain sinus rhythm.

**Correct Answer: A. Adenosine**