Vaughan Williams Class 1 is best described as which mechanism?

Vaughan Williams Class 1 is best described as which mechanism?

• A. Slows fast sodium channels
• B. Inhibits calcium channels
• C. Blocks potassium channels
• D. Beta blockade

Answer: (A)

This item tests the idea that Class I antiarrhythmics work by blocking the fast sodium channels in cardiac tissue. By doing so, they reduce the slope of the phase 0 upstroke of the action potential, which slows conduction velocity through the atria, ventricles, and His-Purkinje system. This slowing helps interrupt reentrant circuits and prevents rapid tachyarrhythmias. Subtypes differ in how they influence the action potential duration, but the defining mechanism across the class is blockade of fast sodium channels. In contrast, calcium channel blockers affect the AV node and plateau phase, potassium channel blockers prolong repolarization, and beta blockers reduce adrenergic drive.

This item tests the idea that Class I antiarrhythmics work by blocking the fast sodium channels in cardiac tissue. By doing so, they reduce the slope of the phase 0 upstroke of the action potential, which slows conduction velocity through the atria, ventricles, and His-Purkinje system. This slowing helps interrupt reentrant circuits and prevents rapid tachyarrhythmias. Subtypes differ in how they influence the action potential duration, but the defining mechanism across the class is blockade of fast sodium channels. In contrast, calcium channel blockers affect the AV node and plateau phase, potassium channel blockers prolong repolarization, and beta blockers reduce adrenergic drive.