An overview of class III electrophysiological agents: a new generation of antiarrhythmic therapy.

Publisher Summary This chapter gives an overview of class III electrophysiological agents, which are considered a new generation of antiarrhythmic therapy. Arrhythmias can range from isolated PVC's, coupled beats, non-sustained ventricular tachyarrhythmias (NSVT), sustained ventricular tachyarrhythmias (SVT) and, ultimately, ventricular fibrillation (VF). It is generally agreed that the most serious arrhythmias, SVT and VF, arise by re-entrant mechanisms. That is, a propagated impulse follows a pathway, which returns to its origin and re-excites the original tissue, thus forming a continuous loop for the aberrant impulse. The re-entrant pathway is dependent on conduction velocity, path length and the refractory period of the tissue. If these parameters remain constant, then an ordered re-entrant mechanism results (for example, NSVT, SVT); if multiple pathways exist and continuously change with time, then random re-entry results (VF). Sufficient change in any one of the parameters breaks the loop and terminates the arrhythmia. Similarly, these parameters (for example, conduction velocity or refractoriness) can be altered in a beneficial manner to prevent a specific re-entrant route from forming.