Antiarrhythmic Drugs Question And Answers

Antiarrhythmic Drugs

Question 1. Enumerate Antiarrhythmic Drugs. Discuss Their Mechanisms And Therapeutic Uses.
Answer:

Enumeration Of Antiarrhythmic Drugs

• Class I: Sodium channel blocker
  • Ia: Quinidine, procainamide, disopyramide
  • Ib: Lignocaine, mexiletine, phenytoin
  • Ic: Flecainide and propafenone.
• Class II: β-blockers, i.e. propranolol
• Class III: Drugs widening atrial pressure, i.e. bretylium
• Class IV: Calcium channel blockers, i.e. nifedipine, verapamil.

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Mechanism Of Antiarrhythmic Drugs

• Antiarrhythmic drugs act by blocking sodium, calcium, and potassium channels.
• The subclass Ia, antiarrhythmic drugs decrease impulse generation and stop abnormal impulse generation.
• Subclass Ib drugs block sodium channels in both activated and inactivated states.
• Subclass Ic, drugs are the most potent sodium channel blockers with more prominent action open state and longest recovery times. They have a variable effect on action potential duration.
• Class II drugs, i.e. β blockers suppress adrenergically mediated ectopic activity.
• Class III drugs increase repolarization. Generally, the potassium channel causes a prolongation of repolarization.
• Class IV drugs are used in paroxysmal supraventricular tachycardia, they slow down SA node and suppress AV conduction.

Therapeutic Uses Of Antiarrhythmic Drugs

• Subclass I, drugs prevent ventricular arrhythmias.
• The subclass Ib drugs are used in arrhythmias following myocardial infarction and cardiac surgery. The drugs are also used in digitalis toxicity.
• Subclass Ic drugs are potent sodium channel blockers. They maintain sinus rhythm in atrial fibrillation.
• Class II drugs are useful in atrial or nodal extrasystole due to emotion/stress.
• Class II drugs are also helpful in digitalis-induced and postmyocardial infarction arrhythmias.
• Class Ill drugs are used in ventricular tachycardia and ventricular fibrillation.
• Class IV drugs are used in paroxysmal supraventricular tachycardia and AV block.