Q. A 32-year-old male with history of recurrent paroxysmal supraventricular tachycardia is stable in sinus rhythm. What is the best choice for long-term prophylaxis?

Correct Answer: A. Oral diltiazem

Paroxysmal supraventricular tachycardia (PSVT) requires long-term prophylaxis in a stable patient—the key discriminator. Oral diltiazem, a non-dihydropyridine calcium channel blocker, is the ideal first-line agent for prophylaxis because it: (1) slows AV nodal conduction and prolongs AV nodal refractoriness, interrupting the reentrant circuit in most PSVT cases (typically AV nodal reentrant tachycardia or orthodromic AVNRT); (2) is administered orally for chronic maintenance; (3) has a favorable side-effect profile with good tolerability in long-term use; (4) is cost-effective and widely available in India. Beta-blockers (e.g., metoprolol) are equally effective alternatives, but diltiazem is preferred when beta-blockers are contraindicated (asthma, COPD, bradycardia). The mechanism relies on slowing conduction through the slow pathway of the AV node, preventing the reentrant loop. Per Harrison and Indian cardiology practice, diltiazem (or verapamil) is the first-line calcium channel blocker for PSVT prophylaxis in hemodynamically stable patients. Dosing typically starts at 60–90 mg three times daily, titrated to effect.

Why the other options are wrong

B. IV adenosine — Adenosine is the acute termination agent for PSVT, not prophylaxis. It has an ultra-short half-life (_{10 seconds) and is given as a rapid IV bolus to acutely convert PSVT to sinus rhythm. It cannot be used for long-term prophylaxis because it is not orally bioavailable and its effect is transient. NBE traps students who confuse acute management with chronic prevention. **C. IV amiodarone** — Amiodarone is reserved for **refractory or hemodynamically unstable PSVT** and carries significant toxicity (thyroid, liver, pulmonary, QT prolongation) that makes it unsuitable for long-term prophylaxis in a stable patient. IV formulation is for acute/critical settings, not chronic oral prophylaxis. This option represents over-treatment and unnecessary toxicity risk. **D. IV Esmolol** — Esmolol is an ultra-short-acting IV beta-blocker used for **acute rate control** in unstable patients or perioperative settings. Its half-life is} 9 minutes; it cannot provide sustained prophylaxis. The IV route and short duration make it unsuitable for long-term maintenance therapy in a stable, outpatient PSVT patient.

High-Yield Facts

Mnemonics

PSVT Prophylaxis: ORAL agents Oral diltiazem/verapamil, Rate-limiting beta-blockers (metoprolol), Avoid adenosine (acute only), Long-term calcium channel blockers. Use this when choosing chronic PSVT management. Acute vs. Chronic PSVT ACUTE: Adenosine (IV), vagal maneuvers. CHRONIC: Diltiazem/verapamil (oral), beta-blockers. Adenosine = 10-second fix; diltiazem = daily pill.

NBE Trap

NBE pairs acute PSVT termination agents (adenosine, IV amiodarone, esmolol) with the question to trap students who confuse acute management with chronic prophylaxis. The word "long-term" is the discriminator that eliminates all IV agents.

Clinical Pearl

In Indian outpatient cardiology, diltiazem is preferred over verapamil for PSVT prophylaxis because it has fewer drug interactions and better GI tolerability. Always ask: "Is this acute or chronic?" before choosing between adenosine (acute) and diltiazem (chronic).

_Reference: Harrison Ch. 231 (Arrhythmias); KD Tripathi Ch. 31 (Antiarrhythmics)_