Vaughan Williams Class 1 (electrolyte function) is associated with which mechanism?

Vaughan Williams Class 1 (electrolyte function) is associated with which mechanism?

• A. Blocks potassium channels
• B. Slows fast sodium channels
• C. Increases calcium influx
• D. Inhibits alpha receptors

Answer: (B)

Fast sodium channel blockade in cardiac cells slows the rate of rise of the action potential (phase 0) and reduces conduction velocity through atrial, ventricular, and Purkinje pathways. This is the defining feature of Vaughan Williams Class I antiarrhythmics, which act by inhibiting the fast inward sodium current. The Class I drugs are subdivided based on their effects on action potential duration and refractoriness, but their common mechanism is blocking these Na+ channels rather than affecting potassium channels, calcium influx, or adrenergic receptors. Therefore, the mechanism described here is slowing of fast sodium channels.

Fast sodium channel blockade in cardiac cells slows the rate of rise of the action potential (phase 0) and reduces conduction velocity through atrial, ventricular, and Purkinje pathways. This is the defining feature of Vaughan Williams Class I antiarrhythmics, which act by inhibiting the fast inward sodium current. The Class I drugs are subdivided based on their effects on action potential duration and refractoriness, but their common mechanism is blocking these Na+ channels rather than affecting potassium channels, calcium influx, or adrenergic receptors. Therefore, the mechanism described here is slowing of fast sodium channels.