Drug of choice for paroxysmal supraventricular tachycardia (PSVT) is:
**Core Concept**
The question is testing the knowledge of the pharmacological management of paroxysmal supraventricular tachycardia (PSVT), a type of abnormal heart rhythm. Adenosine is a medication that works by transiently blocking AV nodal conduction, which is the preferred treatment for PSVT.
**Why the Correct Answer is Right**
Adenosine is the drug of choice for PSVT because it works by selectively blocking the AV node, which is the site of origin for PSVT. This action leads to a transient blockage of AV nodal conduction, thereby interrupting the re-entrant circuit that maintains the PSVT. Adenosine has a very short half-life, which allows for rapid termination of the arrhythmia without causing significant hemodynamic effects.
**Why Each Wrong Option is Incorrect**
**Option A:** Digoxin is not the drug of choice for PSVT because it increases the contractility of the heart and can worsen the arrhythmia.
**Option B:** Lidocaine is an antiarrhythmic medication that is effective for ventricular arrhythmias but is not the first-line treatment for PSVT.
**Option C:** Verapamil is a calcium channel blocker that can be used to treat PSVT, but it is not the preferred initial treatment.
**Clinical Pearl / High-Yield Fact**
Adenosine has a very short half-life (less than 10 seconds), which means that it must be administered as a rapid bolus to be effective.
**Correct Answer: A. Adenosine**