The drug of choice in paroxysmal supraventricular tachycardia is-
**Core Concept**
Paroxysmal supraventricular tachycardia (PSVT) is a type of abnormal heart rhythm originating above the ventricles, characterized by a rapid heart rate. The treatment of choice involves medications that can block the AV node to restore a normal sinus rhythm.
**Why the Correct Answer is Right**
Adenosine is the preferred medication for the acute treatment of PSVT due to its rapid onset of action and short half-life. Adenosine works by transiently blocking the AV node, thereby interrupting the re-entrant circuit responsible for the tachycardia. This leads to a brief pause in the heart rhythm, allowing the heart to return to its normal sinus rhythm. The mechanism of action involves binding to A1 receptors in the AV node, which decreases the firing rate of the AV node.
**Why Each Wrong Option is Incorrect**
**Option A:** Digoxin is a cardiac glycoside that increases the contractility of the heart but is not the first-line treatment for PSVT. It can actually worsen the condition by increasing the heart rate.
**Option B:** Beta-blockers are useful in managing heart rate but are not the preferred treatment for PSVT due to their slower onset of action and potential to worsen the condition.
**Option C:** Calcium channel blockers can be used to manage PSVT but are not as effective as adenosine in rapidly restoring a normal sinus rhythm.
**Clinical Pearl / High-Yield Fact**
Remember the "5 Hs" and "5 Ts" to help diagnose PSVT: Heart failure, Hypokalemia, Hypomagnesemia, Hypothyroidism, Hypoxia, and Tachycardia, Torsades de Pointes, Tricyclic antidepressants, and Triggers (such as caffeine or exercise).
**Correct Answer: A. Adenosine.**