Anti-Arrhythmic Drugs

• Anti-Arrhythmic Drugs are classified based on the Vaughan-Williams classification into four main classes, each with distinct mechanisms of action.
• Learn about Anti-Arrhythmic Drugs including their classes, mechanisms, and clinical uses in treating arrhythmias effectively.
• Cardiac Arrhythmias are disturbances in the normal rhythm or rate of the heartbeat.

Major Classes of Anti-Arrhythmic Drugs:

1. Class I: Sodium Channel Blockers

• Block sodium channels, affecting phase 0 depolarization and slowing conduction velocity.
• Subclasses:

1. Class IA

   • Examples: Quinidine, Procainamide, Disopyramide
   • MOA: Block fast Na⁺ channels, prolong action potential and refractory period.
   • Uses: Ventricular and supraventricular arrhythmias.
   • Side Effects: Proarrhythmia (torsades de pointes), hypotension, GI disturbances.

2. Class IB

   • Examples: Lidocaine, Mexiletine
   • MOA: Preferentially block Na⁺ channels in ischemic/depolarized tissue, shortening action potential.
   • Uses: Acute ventricular arrhythmias, post-MI.
   • Side Effects: CNS effects (seizures, confusion), allergies.

3. Class IC

   • Examples: Flecainide, Propafenone
   • MOA: Strong Na⁺ channel blockade, slowing conduction without prolonging action potential.
   • Uses: Supraventricular and ventricular arrhythmias.
   • Side Effects: Proarrhythmia, bradycardia, hypotension.

2. Class II: Beta-Blockers

• Reduce sympathetic activity, decreasing heart rate and contractility.
• Examples: Propranolol, Metoprolol, Esmolol
• MOA: Block β-receptors, reducing AV node conduction and prolonging refractory periods.
• Uses: Supraventricular and ventricular arrhythmias, ischemic heart disease, and hypertension.
• Side Effects: Bradycardia, fatigue, bronchoconstriction.

3. Class III: Potassium Channel Blockers

• Prolong repolarization by blocking potassium channels.
• Examples: Amiodarone, Sotalol, Dofetilide
• MOA: Prolong action potential and refractory period.
• Uses: Ventricular and supraventricular arrhythmias.
• Side Effects: QT prolongation, torsades de pointes, thyroid and pulmonary toxicity (amiodarone).

4. Class IV: Calcium Channel Blockers

• Block calcium influx, affecting AV node conduction.
• Examples: Verapamil, Diltiazem
• MOA: Inhibit L-type Ca²⁺ channels, reducing automaticity and heart rate.
• Uses: Supraventricular arrhythmias and rate control.
• Side Effects: Bradycardia, hypotension, constipation.

5. Other Anti-Arrhythmic Agents

1. Adenosine:

   • MOA: Activates A1 receptors, transient AV node blockade.
   • Uses: Acute SVT termination.
   • Side Effects: Transient asystole, flushing, chest discomfort.

2. Digoxin:

   • MOA: Inhibits Na⁺/K⁺-ATPase, increasing vagal tone and reducing AV conduction.
   • Uses: Rate control in atrial fibrillation/flutter with heart failure.
   • Side Effects: Toxicity (nausea, vision changes, arrhythmias).

Clinical Considerations:

• Proarrhythmic Risks: Some anti-arrhythmics can induce new or more severe arrhythmias.
• Underlying Heart Disease: Drug choice depends on the presence of structural heart disease.
• Monitoring: Regular ECGs, electrolyte levels, and assessment for drug-specific toxicities.

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