Which category do primary sodium channel blockers fall under in Vaughan-Williams classification?

Primary sodium channel blockers are classified under Class I in the Vaughan-Williams classification system. This classification system is used to categorize antiarrhythmic drugs based on their mechanism of action and effect on cardiac action potential duration.

Class I agents specifically target the sodium channels responsible for the initial depolarization phase of the action potential in cardiac cells. By blocking these channels, they can stabilize the cardiac cell membrane, decrease excitability, and potentially help in arrhythmias management by slowing conduction velocity and prolonging the refractory period in various tissues of the heart.

Class II agents are beta-adrenergic blockers, which primarily act by reducing sympathetic stimulation of the heart, while Class III agents are potassium channel blockers that prolong the action potential and refractory period without directly blocking sodium channels. Class IV agents are calcium channel blockers that work on the calcium channels and are used predominantly in the management of atrial fibrillation and other supraventricular tachycardias.

Thus, since sodium channel blockade is the primary action of Class I antiarrhythmics, this provides clarity on why they fall under this particular category.