Anti-Arrhythmic Drugs

The heart normally beats in a regular rhythm due to the coordinated generation and conduction of electrical impulses through the cardiac conduction system. Any disturbance in the rate, rhythm, or conduction of these impulses is known as an arrhythmia or cardiac dysrhythmia. Arrhythmias may cause palpitations, dizziness, fainting, breathlessness, or, in severe cases, life-threatening conditions such as ventricular tachycardia and ventricular fibrillation. Anti-arrhythmic drugs are medicines used to prevent, suppress, or treat abnormal cardiac rhythms.

Most anti-arrhythmic drugs act by modifying the electrical activity of cardiac cells, particularly sodium (Na⁺), potassium (K⁺), and calcium (Ca²⁺) ion channels, or by altering sympathetic or parasympathetic activity. The commonly used Vaughan–Williams classification divides anti-arrhythmic drugs into four major classes. Class I drugs block fast sodium channels and are further divided into IA, IB, and IC. Class II drugs are β-adrenergic blockers that reduce sympathetic effects on the heart. Class III drugs mainly block potassium channels and prolong cardiac repolarisation. Class IV drugs, mainly verapamil and diltiazem, block L-type calcium channels and particularly affect conduction through the AV node.

Some important anti-arrhythmic drugs do not fit neatly into these four classes. Adenosine produces a very short-lasting AV nodal block and is commonly used for the rapid termination of certain paroxysmal supraventricular tachycardias. Digoxin slows AV nodal conduction mainly by increasing vagal activity.

For pharmacy competitive examinations such as GPAT, NIPER, UPSC Drug Inspector, AIIMS Pharmacist, Railway Pharmacist, SSC, ESIC, and State Pharmacist examinations, important areas include drug classification, mechanism of action, effects on cardiac action potential and ECG, therapeutic uses, adverse effects, and characteristic drug-toxicity associations.

Understanding these concepts provides a strong foundation for solving both direct and challenging conceptual MCQs on anti-arrhythmic drugs.

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