Drugs » Anti-arrhythmia

Anti-arrhythmia

Drugs used in cardiac arrhythmia

These drugs are used to prevent or treat irregularities of cardiac rhythm.

Abnormal automaticity or impaired conduction or both are the main causes of cardiac arrhythmias.

Myocardial ischaemia, electrolyte and pH imbalance, mechanical injury, mechanical stretching, neurogenic and influence &antiarrhythmics themselves can cause arrhythmias by altering electrophysiological properties of cardiac fibres.

Classification

Antiarrhythmic drugs act by blocking myocardial Na+, K+ or Ca++ channels.

Note: Class IA agents also have class III properties. Propranolol has class I action as well. Sotalol and Bretylium have both class II and class III actions.

Note: Class IA agents also have class III properties. Propranolol has class I action as well. Sotalol and Bretylium have both class II and class III actions.

Additionally

1. For Paroxysmal supraventricular tachycardia: Adrenaline, Digitalis.
2. For A-V block:
   Sympathamimetics - Isoprenaline
   Anticholinergics - Atropine
3. Digitalis is used in AF (atrial fibrillation), atrial flutter and paroxysmal supraventricular tachycardia to control ventricular rate.

Choice of Antiarrhythmics
Simple arrhythmias, e.g. most atrial extra-systoles (AES) and occasional ventricular extra systoles (VES) in an otherwise normal heart do not require anti-arrthymic treatment. Chronic prophylactic therapy with class I and class IV anti-arrhythmics does not appear to afford survival benefits, except in few selected cases.

Vigorous therapy is indicated when:

• Arrhythmia is life threatening e.g. sustained ventricular tachycardia (VT).
• Arrhythmia is causing hypotension, breathlessness or cardiac failure.
• Palpitation is marked, e.g. in PSVT, sustained VT, AF, torsades de point.
• When simple arrhythmia may lead to more serious ones,e.g. after MI (warning arrhythmia)

• In the above situations antiarrhythmics are mostly needed for short periods.
• The aim is to improve cardiovascular function either by restoring sinus rhythm or by controlling ventricular rate, or by conversion to a more desirable pattern of electrical and mechanical activity.
• Despite extensive investigations, choice of an antiarrhythmic is still largely empirical.

Choice of drugs for Cardiac Arrhythmias