Hye can you name antiarrhythmic drugs
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antiarrhythmic drugs classification Vaughan Williams mechanism of action
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Here is a comprehensive overview of antiarrhythmic drugs, classified by the Vaughan Williams Classification system:
Antiarrhythmic Drugs — Vaughan Williams Classification
Class I — Sodium Channel Blockers
Block fast Na⁺ channels → slow phase 0 depolarization
| Subclass | Mechanism | Drugs |
|---|---|---|
| Ia | Moderate Na⁺ block + ↑ APD | Quinidine, Procainamide, Disopyramide |
| Ib | Weak Na⁺ block + ↓ APD | Lidocaine, Mexiletine, Phenytoin |
| Ic | Strong Na⁺ block, minimal APD change | Flecainide, Propafenone, Encainide |
Class II — Beta-Blockers
Block β-adrenergic receptors → ↓ SA node automaticity, ↓ AV node conduction
- Metoprolol
- Atenolol
- Propranolol
- Esmolol (short-acting, IV)
- Carvedilol
- Bisoprolol
Class III — Potassium Channel Blockers
Block K⁺ channels → prolong repolarization and action potential duration (APD)
- Amiodarone (also has Class I, II, IV properties)
- Sotalol (also has Class II properties)
- Dronedarone
- Dofetilide
- Ibutilide
- Bretylium
Class IV — Calcium Channel Blockers (Non-dihydropyridines)
Block L-type Ca²⁺ channels → ↓ AV nodal conduction
- Verapamil
- Diltiazem
Unclassified / Miscellaneous Antiarrhythmics
These don't fit neatly into the Vaughan Williams system:
| Drug | Mechanism / Use |
|---|---|
| Adenosine | Activates K⁺ channels → transient AV block; used for SVT termination |
| Digoxin | Vagotonic effect → ↓ AV conduction; used in AF rate control |
| Atropine | Muscarinic antagonist; used for symptomatic bradycardia |
| Magnesium sulfate | Used for Torsades de Pointes and refractory VF |
| Ivabradine | HCN channel blocker → ↓ sinus rate (no effect on AV conduction) |
Key Points to Remember
- Amiodarone is the most commonly used antiarrhythmic — it has properties of all 4 classes.
- Sotalol = Class II + III effects (beta-blocker + K⁺ channel blocker).
- Propafenone = Class Ic + weak Class II (beta-blocking) properties.
- Class Ic drugs (Flecainide, Propafenone) are contraindicated post-MI due to the CAST trial findings (increased mortality).
- Class III drugs can cause QT prolongation and risk of Torsades de Pointes.
(Source: Management of Patients With Ventricular Arrhythmias and Prevention of Sudden Cardiac Death, p. 19)
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