Antiarrhythmic Agent - Singh Vaughan Williams Classification

Singh Vaughan Williams Classification

The Singh Vaughan Williams classification, introduced in 1970 based on the seminal work of Bramah N. Singh in his doctoral thesis at Oxford where Vaughan Williams was his advisor and on subsequent work by Singh and his colleagues in the United States, is one of the most widely used classification schemes for antiarrhythmic agents. This scheme classifies a drug based on the primary mechanism of its antiarrhythmic effect. However, its dependence on primary mechanism is one of the limitations of the Singh-VW classification, since many antiarrhythmic agents have multiple action mechanisms. Amiodarone, for example, has effects consistent with all of the first four classes. Another limitation is the lack of consideration within the Singh-VW classification system for the effects of drug metabolites. Procainamide—a class Ia agent whose metabolite N-acetyl procainamide (NAPA) has a class III action—is one such example. A historical limitation was that drugs such as digoxin and adenosine – important antiarrhythmic agents – had no place at all in the VW classification system. This has since been rectified by the inclusion of class V.

With regards to management of atrial fibrillation, Class I and III are used in rhythm control as medical cardioversion agents whilst Class II and IV are used as rate control agents.

There are five main classes in the Singh Vaughan Williams classification of antiarrhythmic agents:

• 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.