Antiarrhythmics Vaughn Williams Classification

Antiarrhythmics Vaughn Williams Classification Class I Sodium Channel Blockade 

Class la Lengthens duration of action potential (t the refractory period in atrial and ventricular muscle, in SA and AV conduction systems, and Purkinje fibers) 

Class Ic Greater sodium current depression (blocks the fast inward Na current in heart muscle and Purkinje fibers, and slows the rate of t of phase 0 of the action potential) 

Class III Prolong refractory period via action potential 

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Although officially classified as a class III antiarrhythmic, amiodarone possesses electrophysiologic characteristics of all four Vaughn Williams classifications. Acutely, intravenous amiodarone displays mainly antiadrenergic (class II) and calcium channel blocking (class TV) properties. Consequently, hypotension, which occurs in roughly 20% of clinical trials, is a concern. This hypotension is more dependent on the rate of administration than on the amount of drug... 

How should the clinician approach the patient with documented asymptomatic PVCs Clearly, attempts to suppress asymptomatic PVCs should not be made with any antiarrhythmic drug. Indeed, those at risk for arrhythmic death (recent MI, LV dysfunction, complex PVCs) should not be given any type I or III antiarrhythmic agent routinely. Of the antiarrhythmic drugs in the Vaughn Williams classification, only /3-blockers have been proven conclusively to prevent overall mortality in these patients, and therefore, chronic drug therapy should be restricted to these agents. 

Vaughn Williams, E. M., A classification of antiarrhythmic actions reassessed after a decade of new drugs, Clin. J. Pharmacol., 24 129-147, 1984. 

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