Vaughan Williams Class 3 is characterized by which mechanism?

Vaughan Williams Class 3 is characterized by which mechanism?

• A. Inhibits calcium channels
• B. Prolongs atrial refractoriness
• C. Blocks potassium channel
• D. Slows fast sodium channels

Answer: (C)

Blockade of potassium channels slows repolarization, which lengthens the action potential duration and the effective refractory period in cardiac cells. This is the defining action of Vaughan Williams Class III antiarrhythmics, and it helps prevent reentrant tachyarrhythmias by keeping cells in a non‑excitable state longer before they can fire again. Clinically, this also manifests as a lengthened QT interval due to prolonged ventricular repolarization. Other choices describe mechanisms of other classes: blocking calcium channels slows conduction in the AV node (Class IV), and slowing fast sodium channels reduces rapid depolarization (Class I). While some drugs may have multiple effects, the characteristic feature of Class III is potassium channel blockade leading to extended repolarization and refractoriness.

Blockade of potassium channels slows repolarization, which lengthens the action potential duration and the effective refractory period in cardiac cells. This is the defining action of Vaughan Williams Class III antiarrhythmics, and it helps prevent reentrant tachyarrhythmias by keeping cells in a non‑excitable state longer before they can fire again. Clinically, this also manifests as a lengthened QT interval due to prolonged ventricular repolarization.

Other choices describe mechanisms of other classes: blocking calcium channels slows conduction in the AV node (Class IV), and slowing fast sodium channels reduces rapid depolarization (Class I). While some drugs may have multiple effects, the characteristic feature of Class III is potassium channel blockade leading to extended repolarization and refractoriness.