Antiarrhythmic classification into class1a,1b,1c,2,3,4,5 were given by:

The Vaughan Williams classification was introduced in 1970 by Miles Vaughan Williams. 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. Vaughan Williams, EM (1970) Classification of antiarrhythmic drugs. In Symposium on Cardiac Arrhythmias (Eds. Sandoe E, Flensted- Jensen E, Olsen KH). Astra, Elsinore. Denmark (1970) Ref: Tripati 8th ed.