Antiarrhythmic agents and proarrhythmia

The Vaughn Williams classification divides antiarrhythmic agents into four groups according to their effects on various ion channels. Class I agents b lock sodium channels and are subdivided into three groups. The use of class la agents is gradually on the decline, secondary to lack of a favorable ri sk/benefit ratio. Class Ib agents include lidocaine, which is extensively u sed for the acute treatment of ventricular tachyarrhythmias. Class Ic drugs are not advisable for patients with structural cardiac abnormalities secon dary to a high risk of proarrhythmia, They are mainly used for supraventric ular tachyarrhythmias. beta blockers form class II. Class III agents, such as amiodarone and sotalol, prolong action potential duration and repolariza tion and are among the most widely used antiarrhythmics. They are the subje ct of active research, and newer agents are being developed. Calcium-channe l blockers are grouped under class IV. Digoxin and adenosine have unique an tiarrhythmic properties, which can be useful in the management of selected patients, All antiarrhythmic drugs have the potential to provoke arrhythmia s and, therefore, should be used with caution. The risk of proarrhythmia is increased in patients with abnormal cardiac substrate, with electrolyte ab normalities, and during drug initiation. Correction of electrolyte imbalanc e and prevention of bradycardia while the drug is metabolized and/or excret ed are the cornerstones of proarrhythmia management.