Use Dependence and Reverse Use Dependence of Antiarrhythmic Agents: Pro- and Antiarrhythmic Actions

The normal heart beat starts at regular intervals (600–1000 ms) in the SA node, then propagates through the atria to enter the AV node, where conduction is slow. With some delay it enters the His-Purkinje system which quickly activates the ventricular myocardium. When activation of the heart deviates from this normal activation sequence an arrhythmia results. The most serious arrhythmias are those where the normal pumping function of the heart is jeopardized like in fibrillation and tachycardia. In fibrillation, there exists no synchronization between the heart cells so that the pumping of blood stops, while in tachycardia the heart contracts so frequently that it contracts before it has properly filled. As a result cardiac output is very low. Because of the seriousness of these two arrhythmias, I concentrate on the electropharmacology of agents that interfere with tachycardias and fibrillation.