Antiarrhythmic agent

Antiarrhythmic agents, also known as cardiac dysrhythmia medications, are a group of pharmaceuticals that are used to suppress abnormally fast rhythms (tachycardias), such as atrial fibrillation, supraventricular tachycardia and ventricular tachycardia. Many attempts have been made to classify antiarrhythmic agents. Many of the antiarrhythmic agents have multiple modes of action, which makes any classification imprecise. Cardiac action potential The cardiac myocyte has two general types of action potentials: conduction system and working myocardium. The action potential is divided into 5 phases and shown in the diagram. The sharp rise in voltage ("0") corresponds to the influx of sodium ions, whereas the two decays ("1" and "3", respectively) correspond to the sodium-channel inactivation and the repolarizing efflux of potassium ions. The characteristic plateau ("2") results from the opening of voltage-sensitive calcium channels. Each phase utilizes different channels and it is useful to compare these phases to the most common classification system — Vaughan Williams — described below. The Vaughan Williams classification was introduced in 1970 by Miles Vaughan Williams. Vaughan Williams was a pharmacology tutor at Hertford College, Oxford. One of his students, Bramah N. Singh, contributed to the development of the classification system. The system is therefore sometimes known as the Singh-Vaughan Williams classification. The five main classes in the Vaughan Williams classification of antiarrhythmic agents are: Class I agents interfere with the sodium (Na+) channel. Class II agents are anti-sympathetic nervous system agents. Most agents in this class are beta blockers. Class III agents affect potassium (K+) efflux. Class IV agents affect calcium channels and the AV node. Class V agents work by other or unknown mechanisms. With regard to management of atrial fibrillation, classes I and III are used in rhythm control as medical cardioversion agents, while classes II and IV are used as rate-control agents.