Correct Answer: C. Diltiazem
Diltiazem is the calcium channel blocker of choice for atrial flutter prophylaxis because it possesses dual electrophysiological properties: it blocks L-type calcium channels in the AV node (slowing conduction and prolonging the refractory period) AND has intrinsic negative inotropic and chronotropic effects. This makes it uniquely suited for both acute rate control during rapid ventricular response AND long-term prevention of arrhythmia recurrence. Unlike dihydropyridines (felodipine, nifedipine, amlodipine), which are peripheral vasodilators with minimal AV nodal effects, diltiazem (a non-dihydropyridine) directly suppresses ectopic activity in the atrium and slows AV nodal conduction. In Indian clinical practice, diltiazem is the preferred calcium channel blocker for supraventricular arrhythmias per standard cardiology protocols. The 65-year-old patient with recurrent atrial flutter requires an agent that prevents both the arrhythmia initiation and rapid ventricular response—diltiazem achieves both. Verapamil is equally effective but diltiazem is preferred due to better tolerability and fewer drug interactions in elderly patients on multiple medications.
Why the other options are wrong
A. Felodipine — Felodipine is a dihydropyridine calcium channel blocker that acts primarily as a peripheral vasodilator with minimal AV nodal effects. It causes reflex tachycardia and does not suppress atrial ectopy or slow AV nodal conduction—the two mechanisms required for atrial flutter prophylaxis. It may actually worsen arrhythmia by increasing heart rate. NBE trap: students may confuse 'calcium channel blocker' with 'suitable for arrhythmia control' without recognizing the critical distinction between dihydropyridine and non-dihydropyridine subtypes. B. Nifedipine — Nifedipine is a short-acting dihydropyridine with potent peripheral vasodilation but negligible AV nodal effects. It does not suppress atrial ectopic activity and causes reflex sympathetic activation, potentially increasing heart rate and worsening atrial flutter. Long-acting nifedipine has better hemodynamic stability but still lacks the antiarrhythmic properties needed for prophylaxis. It is contraindicated in supraventricular arrhythmias requiring rate control. D. Amlodipine — Amlodipine is a long-acting dihydropyridine with excellent peripheral vasodilation but no AV nodal blocking properties. While it provides sustained blood pressure control, it does not slow AV nodal conduction or suppress atrial ectopy—both essential for atrial flutter prophylaxis. Its long half-life does not compensate for the absence of antiarrhythmic efficacy. It is suitable for hypertension but not for arrhythmia management.
High-Yield Facts
- Non-dihydropyridine calcium channel blockers (diltiazem, verapamil) block AV nodal conduction; dihydropyridines (nifedipine, felodipine, amlodipine) cause reflex tachycardia and worsen SVT.
- Diltiazem is the preferred calcium channel blocker for atrial flutter prophylaxis because it combines AV nodal blockade with suppression of atrial ectopic activity.
- Dihydropyridines are contraindicated in supraventricular arrhythmias without concurrent beta-blocker or non-dihydropyridine co-therapy due to risk of paradoxical tachycardia.
- Diltiazem dosing: 60–120 mg TDS (immediate-release) or 180–360 mg once daily (extended-release) for arrhythmia prophylaxis in Indian practice.
- Verapamil is equally effective as diltiazem for atrial flutter but has higher risk of constipation, AV block, and drug interactions—diltiazem is preferred in elderly patients.
Mnemonics
DV for SVT (Non-dihydropyridines for Arrhythmias) Diltiazem and Verapamil → AV nodal blockade → SVT/atrial flutter control. Dihydropyridines (Felodipine, Nifedipine, Amlodipine) → Peripheral vasodilation → Reflex tachycardia → Worsen arrhythmias. Memory Hook: 'Diltiazem Delays' Diltiazem Delays AV nodal conduction (slows HR, suppresses ectopy). Dihydropyridines Dilate vessels (reflex tachycardia, worsen arrhythmias). Use this to instantly distinguish when choosing for arrhythmia prophylaxis.
NBE Trap
NBE pairs "calcium channel blocker" with "arrhythmia control" to trap students who memorize drug classes without understanding mechanism. The question tests whether students know that only non-dihydropyridine calcium channel blockers (diltiazem, verapamil) have antiarrhythmic properties—dihydropyridines are contraindicated in SVT.
Clinical Pearl
In Indian outpatient cardiology practice, a 65-year-old with recurrent atrial flutter on diltiazem 180 mg daily often achieves both rate control (resting HR 60–80 bpm) and reduced arrhythmia recurrence without the constipation burden of verapamil—critical for medication adherence in elderly patients managing multiple comorbidities.
_Reference: KD Tripathi Pharmacology Ch. 31 (Antiarrhythmic Drugs); Harrison Principles of Internal Medicine Ch. 226 (Arrhythmias)_