Anti-arrhythmic drugs

Anti-arrhythmic drugs

Antiarrhythmic drugs are a group of pharmaceuticals that are used to suppress abnormal rhythms of the heart (cardiac arrhythmias), such as atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation.

Class I antiarrhythmics interfere with sodium channel function, and are subdivided by the effect they have on the action potential (AP)- see figure below

Class 1a antiarrhythmics

e.g. disopyramide (used for the prevention and treatment of ventricular and supraventricular arrhythmias and maintenance of sinus rhythm after cardioversion)

Class 1b antiarrhythmics

e.g. lidocaine (as well as being a local anaesthetic, lidocaine can be used to treat ventricular arrhythmias, and as an alternative for cardiopulmonary resuscitation if amiodarone is not available)

Class Ic antiarrhythmics

e.g. flecainide (used to treat various arrhythmias: AV nodal reciprocating tachycardia, arrhythmias associated with Wolff-Parkinson-White syndrome and supraventricular arrhythmias) and propafenone (mainly used under specialist supervision in hospital to treat supraventricular arrhythmias and paroxysmal supraventricular tachyarrhythmias which include paroxysmal atrial flutter or fibrillation and paroxysmal re-entrant tachycardias involving the AV node or accessory pathway, where standard therapy ineffective or contra-indicated).

Class II antiarrhythmics are conventional beta blockers- See the beta-adrenoceptor blocking drugs topic above this one

Class III antiarrhythmics (primarily affect potassium (K+) efflux, prolonging repolarization)

e.g. dronedarone (used to treat life-threatening atrial flutter and fibrilation, and to maintain sinus rhythm after cardioversion) and amiodarone (used to treat angina and arrhythmias). Note that amiodarone should not be given alongside sofosbuvir with daclatasvir, sofosbuvir and ledipasvir, and simeprevir with sofosbuvir due to a risk of severe bradycardia and heart block.

Class IV antiarrhythmics (are slow calcium channel blockers, decrease AV node conduction and shorten AP plateau)

e.g. verapamil and diltiazem

Class V (other) antiarrhythmics

e.g. digoxin (decreases speed of conduction through AV node, used to treat congestive heart failure and atrial fibrillation), adenosine (used intravenously for terminating supraventricular tachycardias), magnesium sulfate (used to treat torsades de pointes)

In relation to the classification above, and management of atrial fibrillation, class I and III antiarrhythmics are used in rhythm control as medical cardioversion agents while class II and IV antiarrhythmics are used as rate control agents.