Antiarrhythmic drugs Vaughan Williams classification

Table 2. Examples of antiarrhythmic drugs (Vaughan-William s classification)...

Table 9.1 Antiarrhythmics (modified Vaughan Williams classification) Class I Membrane stabilising drugs...

Antiarrhythmic Drugs. Table 1 Classification of antiarrhythmic drugs according to Vaughan-Williams... 

Describe the modified Vaughan-Williams classification of antiarrhythmic drugs, and compare and contrast the effects of available antiarrhythmic drugs on ventricular conduction velocity, refractory period, automaticity, and inhibition of specific myocardial ion channels. 

The Vaughan-Williams classification of antiarrhythmic drugs has been criticized for a number of reasons. The classification is based on the effects of drugs on normal, rather than diseased, myocardium. In addition, many of the drugs may be placed into more than one class. For example, the class IA drugs prolong repolarization/refractoriness, either via the parent drug8,9 or an active metabolite,10 and therefore also maybe placed in class III. Sotalol is also a 3-blocker, and therefore fits into class II. Amiodarone inhibits sodium and potassium channels, is a non-competitive inhibitor of 3-receptors, and inhibits calcium... 

Blockers are antiarrhythmics of class II according to the Vaughan-Williams classification, effective in the treatment of both supraventricular and ventricular tachyarrhythmias. These drugs can also reduce ectopic beats, especially if they are a result of sympathetic activity. Sotalol is a racemic mixture of the -blocking L-isomer and the class III antiarrhythmic D-isomer. This racemic mixture as well as D-sotalol are used as class Ill-antiarrhythmic. 

Class 1, II, III, and IV drugs A method for classifying antiarrhythmic drugs, sometimes called the Vaughan-Williams classification based loosely on the channel or receptor affected... 

This section is mainly concerned with the class I antiarrhythmics, which also possess some local anaesthetic properties, and with class IH antiarrhythmics. Antiarrhythmics that fall into other classes are dealt with under beta blockers , (p.833), digitalis glycosides , (p.903), and calcium-channel blockers , (p.860). Some antiarrhythmics that do not fit into the Vaughan Williams classification (see Table 9.1 , (below)) are also included in this section (e.g. adenosine). Interactions in which the an-tiarrhythmic drug is the affecting substance, rather than the drug whose activity is altered, are dealt with elsewhere. 

The most frequently used classification system is that proposed by Vaughan Williams (Table 6-1). Type la drugs slow conduction velocity, prolong refractoriness, and decrease the automatic properties of sodium-dependent (normal and diseased) conduction tissue. Type la drugs are broad-spectrum antiarrhythmics, being effective for both supraventricular and ventricular arrhythmias. 

Vaughan Williams EM. A classification of antiarrhythmic actions reassessed after a decade of new drugs. J Clin Pharmacol 1984 24(4) 129-47. 

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