A patient with paroxysmal supraventricular tachycardia (PSVT) requires treatment for prophylaxis. Which drug is appropriate?

Correct Answer: C. Verapamil

Verapamil is the gold-standard prophylactic agent for paroxysmal supraventricular tachycardia (PSVT), particularly in AV-nodal reentrant tachycardia (AVNRT) and AV-reentrant tachycardia (AVRT). As a non-dihydropyridine calcium channel blocker, verapamil slows AV nodal conduction velocity and increases the AV nodal refractory period—the two critical mechanisms that prevent reentry circuit perpetuation. Unlike acute-phase drugs (adenosine, IV esmolol), verapamil provides sustained suppression when given orally as a long-acting formulation (120–240 mg daily in divided doses). It reduces the frequency and severity of PSVT episodes by raising the threshold for reentry. In Indian clinical practice, verapamil is preferred over beta-blockers in patients without contraindications (asthma, heart failure) because of superior efficacy in nodal reentry and better tolerability. The drug is particularly effective in AVNRT, which accounts for ~60% of PSVT cases in Indian populations. Verapamil also has negative inotropic and chronotropic effects, making it ideal for long-term rhythm control in hemodynamically stable patients.

Why the other options are wrong

A. IV esmolol — Esmolol is an ultra-short-acting IV beta-blocker used only for acute termination of PSVT in hospital settings, not prophylaxis. Its half-life is _{9 minutes; it cannot provide sustained suppression. The question explicitly asks for prophylactic therapy, which requires an oral agent with long duration of action. Esmolol is appropriate for acute SVT in the ICU but inappropriate for outpatient long-term prevention. **B. IV adenosine** — Adenosine is the **first-line acute terminator** of PSVT (especially AVNRT/AVRT) due to its rapid AV nodal blockade and ultra-short half-life (}6 seconds). However, it has no role in prophylaxis—it cannot be given orally and provides no sustained effect. The question asks for prophylactic treatment, not acute conversion. Adenosine is a trap for students who confuse acute management with long-term prevention. D. Oral phenytoin — Phenytoin is an antiarrhythmic with limited efficacy in PSVT and is not recommended for prophylaxis by any major guideline (ACC/AHA, Indian cardiology guidelines). It has no selective AV nodal effects and is primarily used in atrial fibrillation or ventricular arrhythmias. Phenytoin is outdated for PSVT prophylaxis and represents a historical distractor; modern practice favors beta-blockers, calcium channel blockers, or flecainide.

High-Yield Facts

Mnemonics

PSVT Prophylaxis: VERAPAMIL First Verapamil (or Valium-like CCB) = Very good for long-term PSVT prevention. Adenosine = Acute only. Beta-blockers = Backup if verapamil contraindicated. Acute vs. Prophylactic SVT Drugs ACUTE (IV, fast-acting): Adenosine, Esmolol. PROPHYLACTIC (Oral, sustained): Verapamil, Beta-blockers, Flecainide. Remember: 'Acute = Adenosine/Esmolol; Prophylaxis = Persistent verapamil.'

NBE Trap

NBE pairs adenosine and esmolol (both acute-phase drugs) with verapamil to test whether students confuse acute PSVT termination with long-term prophylaxis. Students who know adenosine is "the PSVT drug" may reflexively choose it without reading "prophylaxis" in the stem.

Clinical Pearl

In Indian outpatient cardiology, a patient presenting with recurrent PSVT episodes (2–3 per week) is started on oral verapamil 120 mg BD after acute termination with IV adenosine. This dual approach—acute control + prophylaxis—prevents hospital readmissions and reduces patient anxiety in a resource-limited setting where catheter ablation may not be immediately available.

_Reference: KD Tripathi Pharmacology Ch. 31 (Antiarrhythmics); Harrison Principles of Internal Medicine Ch. 226 (Arrhythmias)_