Antiarrhythmic Drugs
Antiarrhythmics are medications used to prevent and treat abnormal heart rhythms (arrhythmias). These drugs work by modifying the electrical impulses in the heart to restore a normal rhythm and improve heart function.
Classification (Vaughan-Williams Classification System)
- 1. Class I: Sodium Channel Blockers
- IA (Moderate Na+ Block, Prolong Repolarization): Quinidine
- IB (Weak Na+ Block, Shorten Repolarization): Lidocaine
- IC (Strong Na+ Block, Little Effect on Repolarization): Flecainide
- 2. Class II: Beta Blockers
- Propranolol, Metoprolol, Atenolol
- 3. Class III: Potassium Channel Blockers
- Amiodarone, Sotalol, Dofetilide
- 4. Class IV: Calcium Channel Blockers (CCBs)
- Verapamil, Diltiazem
- 5. Class V: Others (Miscellaneous Antiarrhythmics)
- Adenosine
- Atropine
- Digoxin
Pharmacodynamics (Mechanism of Action)
- 1. Class I: Sodium Channel Blockers
- Block sodium (Na+) channels, reducing excitability of cardiac cells and stabilizing the cell membrane.
- Class IA: Prolong repolarization (e.g., Quinidine).
- Class IB: Shorten repolarization (e.g., Lidocaine).
- Class IC: Little effect on repolarization (e.g., Flecainide).
- 2. Class II: Beta Blockers
- Reduce sympathetic nervous system activity, slowing the heart rate and AV node conduction, which helps prevent tachyarrhythmias.
- 3. Class III: Potassium Channel Blockers
- Block potassium (K+) channels, prolonging repolarization and increasing the refractory period, preventing abnormal electrical activity (e.g., Amiodarone, Sotalol).
- 4. Class IV: Calcium Channel Blockers (CCBs)
- Block calcium (Ca²⁺) channels, slow AV node conduction, and decrease heart rate, which helps control supraventricular arrhythmias (e.g., Verapamil, Diltiazem).
- 5. Class V: Miscellaneous
- Adenosine: Temporarily blocks AV node conduction, used in supraventricular tachycardia (SVT).
- Atropine: Increases heart rate, used in bradycardia.
- Digoxin: Increases vagal tone, slows heart rate, and controls atrial fibrillation.