Anti-Arrhythmic Drugs

Anti-arrhythmic drugs correct irregular heartbeats by altering cardiac impulses to restore normal rhythm and heart function.

• Anti-arrhythmic drugs are medications used to treat and prevent abnormal heart rhythms (arrhythmias).
• These drugs work by modifying the electrical activity of the heart to restore and maintain a normal heart rhythm, thereby ensuring efficient blood circulation throughout the body.

Pathophysiology of Arrhythmias

• Arrhythmias occur due to disturbances in the normal electrical conduction system of the heart. These disturbances can result from:
• Enhanced Automaticity: Increased spontaneous depolarization of cardiac cells.
• Triggered Activity: Abnormal depolarizations during or after repolarization.
• Reentrant Circuits: Circular electrical pathways that perpetuate abnormal rhythms.
• Anti-arrhythmic drugs aim to correct these disturbances by targeting various aspects of cardiac electrophysiology.

Classification of Anti-Arrhythmic Drugs

• Anti-arrhythmic drugs are primarily classified according to the Vaughan Williams Classification, which categorizes these medications based on their primary mechanism of action on cardiac cells.

1. Class I: Sodium Channel Blockers

   • • These drugs inhibit sodium (Na⁺) channels, reducing the rate of rise of the action potential (phase 0) in cardiac cells. They are further subdivided into:
   • Class IA
     • Mechanism: Moderate blockade of Na⁺ channels; also block potassium (K⁺) channels, prolonging action potential duration and refractory period.
     • Drugs:
       • Quinidine Sulphate
       • Procainamide Hydrochloride
       • Disopyramide Phosphate
     • Uses: Atrial and ventricular arrhythmias.
     • Side Effects: Prolonged QT interval, torsades de pointes, hypotension.
   • Class IB
     • Mechanism: Mild blockade of Na⁺ channels; shorten action potential duration and refractory period.
     • Drugs:
       • Lidocaine Hydrochloride
       • Phenytoin Sodium
       • Tocainide Hydrochloride
     • Uses: Ventricular arrhythmias, especially post-myocardial infarction.
     • Side Effects: CNS toxicity (e.g., seizures, tremors), numbness.
   • Class IC
     • Mechanism: Potent blockade of Na⁺ channels with minimal effect on action potential duration.
     • Drugs:
       • Mexiletine Hydrochloride
       • Lorcainide Hydrochloride
     • Uses: Atrial and ventricular arrhythmias.
     • Side Effects: Bradycardia, hypotension, proarrhythmic effects.

2. Class II: Beta Blockers

   • • These drugs block beta-adrenergic receptors, decreasing the effects of sympathetic stimulation on the heart.
     • Mechanism: Reduce heart rate, myocardial contractility, and conduction velocity through the atrioventricular (AV) node.
     • Drugs:
       • Sotalol
     • Uses: Atrial fibrillation, ventricular arrhythmias, prevention of arrhythmic recurrence.
     • Side Effects: Bradycardia, hypotension, fatigue, bronchoconstriction.

3. Class III: Potassium Channel Blockers

   • These drugs primarily block K⁺ channels, leading to prolonged repolarization and extended action potential duration.
   • Mechanism: Prolong the QT interval and the refractory period without affecting Na⁺ or Ca²⁺ channels significantly.
   • Drugs:
     • Amiodarone
   • Uses: Atrial fibrillation, ventricular tachycardia, ventricular fibrillation.
   • Side Effects: Pulmonary fibrosis, thyroid dysfunction, liver toxicity, corneal deposits.

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