Which drug belongs to Class 1C of the Vaughan Williams classification?

Class 1C of the Vaughan Williams classification is characterized by drugs that primarily block sodium channels and have a strong effect on the conduction velocity in cardiac tissues. Propafenone is categorized in this class due to its effectiveness in treating various tachyarrhythmias by prolonging the refractory period in both atrial and ventricular tissues and reducing the excitability of these tissues. It works by slowing down the conduction of electrical impulses through the myocardium, making it effective in controlling arrhythmias.

In contrast, the other drugs listed belong to different classes as follows:

• Ibutilide is a Class III antiarrhythmic agent that primarily acts by blocking potassium channels, leading to prolongation of the action potential duration and refractory period.

• Lidocaine is a Class 1B drug that is also a sodium channel blocker but is typically used for ventricular arrhythmias and has a weaker effect on conduction compared to Class 1C drugs.

• Dronedarone is classified as a Class III agent with additional properties affecting different ion channels, which is distinct from the characteristics of Class 1C drugs.

Thus, Propafenone's classification as a Class 1C antiarrhythmic drug is due to its potent sodium channel blocking effects and