What is an example of a Class 1c antiarrhythmic drug?

Class 1c Antiarrhythmic Drugs

Propafenone (option A) is the only Class 1c antiarrhythmic drug among the given options. 1

Classification of Antiarrhythmic Drugs

According to the Vaughan Williams Classification system, antiarrhythmic drugs are categorized into different classes based on their mechanism of action:

• Class I: Sodium channel blockers
  • Class IA: Disopyramide, Procainamide, Quinidine
  • Class IB: Lidocaine, Mexiletine
  • Class IC: Flecainide, Propafenone
• Class II: Beta blockers (e.g., propranolol)
• Class III: Potassium channel blockers (e.g., amiodarone, sotalol, dofetilide, ibutilide)
• Class IV: Calcium channel blockers (e.g., verapamil, diltiazem)

Analysis of the Options

1. Propafenone (A): This is a Class IC antiarrhythmic drug as clearly indicated in the ACC/AHA/ESC guidelines 1. It blocks sodium channels with slow binding kinetics and also has beta-blocking properties 2.

2. Sotalol (B): This is classified as a Class III antiarrhythmic drug that primarily blocks potassium channels, not a Class IC agent 1.

3. Procainamide (C): This is classified as a Class IA antiarrhythmic drug that blocks sodium channels with intermediate kinetics 1.

4. Adenosine (D): This is not included in the Vaughan Williams classification system. It acts primarily on adenosine receptors to slow conduction through the AV node.

Characteristics of Propafenone as a Class IC Agent

Propafenone has several distinctive features:

• It markedly slows cardiac conduction while only modestly prolonging refractoriness 3
• It causes dose-related changes in PR interval and QRS duration 4
• It has additional Class II (beta-blocking) effects, which distinguishes it from other Class IC agents like flecainide 2, 5
• It also demonstrates some potassium channel blocking properties 6

Clinical Applications and Cautions

Propafenone is used for:

• Conversion of recent-onset atrial fibrillation 1
• Treatment of supraventricular tachycardias, particularly those involving reentry mechanisms 1

Important cautions:

• Contraindicated in patients with structural heart disease 7
• Can cause proarrhythmic effects, though possibly less frequently than other Class IC agents 5
• Should be used cautiously or avoided in patients with heart failure or severe obstructive lung disease 1

The classification of propafenone as a Class IC antiarrhythmic drug is well-established in cardiology guidelines and pharmacological literature, making it the correct answer among the provided options.