The drug of choice for paroxysmal supraventricular tachycardia
**Core Concept**
Vagal maneuvers and certain medications are used to manage paroxysmal supraventricular tachycardia (PSVT) by interrupting the re-entrant circuit or slowing conduction through the atrioventricular (AV) node. This is typically achieved by administering a medication that blocks AV nodal conduction or slows the heart rate.
**Why the Correct Answer is Right**
The drug of choice for PSVT is **Adenosine**. Adenosine works by transiently blocking AV nodal conduction, which can interrupt the re-entrant circuit and terminate the tachycardia. It has a very short half-life, making it ideal for this purpose. Adenosine binds to A1 receptors on the AV node, which leads to a decrease in AV nodal conduction velocity and a subsequent decrease in heart rate.
**Why Each Wrong Option is Incorrect**
**Option A:** **Digoxin** is incorrect because while it can slow AV nodal conduction, it is not the first-line treatment for PSVT and can actually worsen the situation by increasing the risk of ventricular arrhythmias.
**Option B:** **Lidocaine** is incorrect because it is primarily used for ventricular arrhythmias and does not effectively terminate PSVT.
**Option C:** **Amiodarone** is incorrect because while it can be used for PSVT, it is not the first-line treatment and can have significant side effects.
**Clinical Pearl / High-Yield Fact**
The "Vagal maneuver" of the Valsalva maneuver, carotid massage, or diving reflex can also be used to terminate PSVT by stimulating the vagus nerve and increasing parasympathetic tone, which can slow AV nodal conduction.
**Correct Answer:** A. Adenosine