Pharm 101: Antiarrhythmic Agents

Classification system

Vaughan-Williams classification (four classes)

Class I
  • Act via Na channel blockade
  • Subclasses reflect effects on:
    • Action potential duration (APD)
    • Kinetics of Na channel blockade
IAProcainamide, Quinidine, DisopyramideProlong APD, dissociate (from channel) with intermediate kinetics
IBLignocaineShorten APD in heart, dissociate with rapid kinetics
ICFlecainide, PropafenoneMinimal effects on APD, dissociated with slow kinetics
Class II
  • Sympatholytic
  • Beta-adrenergic blocking activity
  • Examples:
Class III
  • Prolong APD
  • Block rapid component of delayed rectifier K current, IKr
  • Examples:
Class IV
  • Blockade of cardiac calcium current
  • Slows conduction in regions where AP upstroke is calcium dependent, e.g. SA and AV nodes
  • Examples:
Other information
  • Drugs may have multiple classes of action e.g. amiodarone shares all four classes of action
  • Certain agents do not fit this classification scheme:
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MBBS CCPU (RCE, Biliary, DVT, E-FAST, AAA) Rob is an Emergency Medicine Advanced Trainee based in Melbourne, Australia. He has special interests in medical education, ECG interpretation, and the use of diagnostic and procedural ultrasound in the undifferentiated and unwell patient.

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