Classification of Antiarrhythmic Drugs

Frequently asked questions

Which specific drugs belong to subclass IA of antiarrhythmic agents?

Subclass IA antiarrhythmic drugs include quinidine, procainamide, and disopyramide. These agents are sodium and potassium channel blockers that prolong phases 0, 3, and 4 of the action potential. Their use is associated with specific adverse effects:

• Quinidine — causes cinchonism (headache, tinnitus, visual disturbances).
• Procainamide — can induce drug-induced lupus.
• Disopyramide — exhibits anticholinergic effects (dry mouth, urinary retention, constipation).

How do subclass IB drugs affect the duration of the cardiomyocyte action potential?

Subclass IB drugs do not prolong the duration of the cardiomyocyte action potential. Unlike other subclasses, the QT interval on the ECG does not increase with their use. These medications (lidocaine, mexiletine) bind to inactivated sodium channels. They are most effective at high heart rates, when channels spend more time in the inactivated state, and have little effect during bradycardia and normal sinus rhythm.

What is the mechanism of action of class II antiarrhythmic drugs?

The mechanism of action of class II antiarrhythmic drugs is $\beta$-adrenergic receptor blockade. This group of drugs is used for tachyarrhythmias and extrasystoles. Specifically, they are a target therapy for re-entrant tachycardias by acting on the atrioventricular node. However, their use carries risks: in Wolff-Parkinson-White syndrome, beta-blockers can increase ventricular rate if atrial fibrillation occurs with conduction over an accessory pathway.

Which medications are included in class III antiarrhythmic drugs?

Class III antiarrhythmic drugs include agents whose primary mechanism of action is potassium channel blockade. The group is pharmacologically heterogeneous and includes:

• Amiodarone — a mixed-action drug whose mechanism includes K⁺ channel blockade and other effects.
• Sotalol — a mixed-action agent combining K⁺ channel-blocking properties and a $\beta$-blocker.
• Ibutilide — a selective K⁺ channel blocker.
• Nibentan — a selective K⁺ channel blocker.

The electrophysiological effect of Class III drugs involves delayed repolarization and increased overall action potential duration.

What is the mechanism of action of class IV antiarrhythmic drugs?

The mechanism of action of class IV antiarrhythmic drugs is calcium channel blockade. Voltage-gated L-type calcium channels predominate in the heart and blood vessels; they open upon membrane depolarization, allowing calcium ions to enter the cell. The group is heterogeneous, and channel sensitivity depends on the chemical structure of the drug. Non-dihydropyridine calcium channel blockers are used as antiarrhythmics in this class:

• Verapamil — a non-dihydropyridine calcium antagonist.
• Diltiazem — a non-dihydropyridine calcium antagonist.

Which antiarrhythmic drugs are not included in the Vaughan-Williams classification?

In addition to the four main classes of antiarrhythmics, the materials highlight additional agents:

• Adenosine — effective for supraventricular tachyarrhythmias.
• Cardiac glycosides — effective for supraventricular tachyarrhythmias.
• Potassium and magnesium preparations — effective for extrasystoles in the setting of hypokalemia.

What is the basis for the classification of antiarrhythmic drugs?

The classification is based on the clinical applications and mechanisms of action of the drugs.

Who authored the primary classification and in what year was it introduced?

The basic classification was proposed by Vaughan-Williams in 1970, with subsequent additions.

What were Class I drugs previously called?

These medications were formerly known as "membrane-stabilizing agents".

Into which subclasses is Class I divided, and what are the criteria?

They are divided into subclasses IA, IB, and IC based on three criteria: nuances of channel binding, effects on cardiac electrophysiology, and clinical application.