Editing Antiarrhythmic agent (section)

===History===
The initial classification system had 4 classes, although their definitions different from the modern classification. Those proposed in 1970 were:<ref name=VW70/>
# Drugs with a direct membrane action: the prototype was [[quinidine]], and [[lidocaine|lignocaine]] was a key example. Differing from other authors, Vaughan-Williams describe the main action as a slowing of the rising phase of the action potential.
# Sympatholytic drugs (drugs blocking the effects of the [[sympathetic nervous system]]): examples included [[bretylium]] and [[Beta blocker|adrenergic beta-receptors blocking drugs]]. This is similar to the modern classification, which focuses on the latter category.
# Compounds that prolong the action potential: matching the modern classification, with the key drug example being [[amiodarone]], and a surgical example being [[thyroidectomy]]. This was not a defining characteristic in an earlier review by Charlier et al. (1968),<ref>{{cite journal|last1=Charlier|first1=R|last2=Deltour|first2=G|last3=Baudine|first3=A|last4=Chaillet|first4=F|title=Pharmacology of amiodarone, and anti-anginal drug with a new biological profile.|journal=Arzneimittel-Forschung|date=November 1968|volume=18|issue=11|pages=1408–1417|pmid=5755904}}</ref> but was supported by experimental data presented by Vaughan Williams (1970).{{r|VW70|p=461}} The figure illustrating these findings was also published in the same year by Singh and Vaughan Williams.<ref>{{cite journal|last1=Singh|first1=BN|last2=Vaughan Williams|first2=EM|title=The effect of amiodarone, a new anti-anginal drug, on cardiac muscle.|journal=British Journal of Pharmacology|date=August 1970|volume=39|issue=4|pages=657–667|pmid=5485142|doi=10.1111/j.1476-5381.1970.tb09891.x|pmc=1702721}}</ref>
# Drugs acting like [[diphenylhydantoin]] (DPH): mechanism of action unknown, but others had attributed its cardiac action to an indirect action on the brain;<ref>{{cite journal|last1=Damato|first1=Anthony N.|title=Diphenylhydantoin: Pharmacological and clinical use|journal=Progress in Cardiovascular Diseases|date=1 July 1969|volume=12|issue=1|pages=1–15|doi=10.1016/0033-0620(69)90032-2|pmid=5807584}}</ref> this drug is better known as antiepileptic drug [[phenytoin]].