Antiarrhythmic drugs have historically been segregated by the Vaughn Williams classification system into four main groups, based on their predominant mechanism of action. This is a good starting point for organizing one's thinking about the various antiarrhythmic drugs, but it is a great oversimplification and does not address several drugs that have electrophysiological effects characteristic of more than one group. Thus, although the grouping of antiarrhythmic agents into four classes is convenient, such a classification falls short of explaining the underlying mechanisms by which many drugs ultimately exert their therapeutic antiarrhythmic effect. Also, certain agents do not fall neatly into the four classes; these are discussed at the end of the chapter.
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