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Antiarrhythmic Drugs

Cardiac Arrhythmias

The abnormalities of cardiac rhythm which may arise from:

a. Abnormality in automaticity
–           Increased firing from pre-existing dormant pacemaker
–           Emergence of an autonomous pacemaker

Due to

    1. Diseases, ischemia, myocarditis, stress
    2. Drugs (digitalis, atropine, sympathomimetics, catecholamines)
    3. Electrolyte imbalance leading to hypokalemia and hypocalcaemia, acidosis

b. Abnormality in conduction
–           complete or partial AV block
–           Re-entrant phenomenon

 Abnormalities Of Impulse Propagation

Circus movement (Re-enterant Arrhythmias)

Damage to certain part of heart results in fibrosis. The refractory period of this part is prolonged. Once the normal impulse reaches, the refractory period is over and it re-enters, exciting fibers, as a result vicious cycle occurs, known as re-entrant phenomenon.

Treatment
  1. Decrease refractory period of damaged part
  2. Further prolong refractory period.

Classification (Vaughan Williams classification)

 Class 1: sodium channel blockers (membrane stabilizing agents)
Class 1A (Cause Moderate Phase “0” Depression. Prolong Action Potential Duration)

Quinidine

Procainamide

Disopyramide

Class 1B (Cause Minimal Phase “0” Depression, Shorten Action Potential Duration)

Lignocaine

Phenytoin

Mexiletene

Tocainide

Class 1c (Cause Marked Phase “0” Depression, Little Effect on Action Potential Duration)

Encainide

Flecainide

Lorcainide

Propaphenone

Class. II Beta Adrenergic Blockers

Esmolol, Propanolol, etc.

Class III (Drugs That Prolong Repolarization)

Amiodarone

Bretylium

Sotalol

Class IV Calcium Channel Blockers

Verapamil

Diltiazem

Miscellaneous

Adenosine

Digoxin (supraventricular arrhythmias)

Magnesium

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Sodium channel blockers (Class 1 antiarrhythmics)

Beta Adrenergic Blockers (Class II antiarrhythmics)

Potassium channel blockers (Class III antiarrhythmics)

Calcium channel blockers (Class IV antiarrhythmics)

Miscellaneous antiarrhythmic drugs

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