Antiarrhythmics - Vaughan Williams Classification:

CLASS 1 - Sodium Channel Blockers:

 • MOA: Block fast Na+ channels to reduce speed of ion conduction

 • ↓ slope of phase 0 to decrease rate and magnitude of depolarization

 • Divided into 3 categories based on Na+ channel blocking effects and AP duration:

    - CLASS 1A: Moderate Blockade, Intermediate Action, ↑ EFR & AP duration

    - CLASS 1B: Weak Blockade, Fast Action, ↓ EFR & AP duration

    - CLASS 1C: Strong Blockade, Slow Action,  ←→ EFR & AP duration

CLASS 2 - Beta Blockers:

 • MOA: Inhibit B.adrenergic activation (↓ cAMP and Ca++ current) causing ↓SA node and AV node activity (rate control)

 • ↓ slope of phase 4 to slow depolarization

 • ↑ PR interval to prolong AV node repolarization

CLASS 3 - Potassium Channel Blockers:

 • MOA: Block K+ channels (primarily) and block alpha & beta adrenergic receptors, and Ca & Na channels.

    - ↑ duration of phase 2 (↑ERP & ↑AP Duration)

    - ↑ QT interval (delays time repolarization)

CLASS 4 - Calcium Channel Blockers:

 • MOA: Block slow Ca++ channels to prevent Ca++ influx into cells (rate control).

    - ↓ slope of phase 0 and 4 to ↑ ERP (slow conduction velocity)

    - ↑ PR interval to prolong AV node repolarization

    - ↓ contraction force (negative inotropy)



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