Early afterdepolarizations and arrhythmogenesis. Experimental and clinical aspects

There is growing evidence that early afterdepolarizations (EADs) and EAD-induced triggered activity play a significant role in the clinical syndrome of long QTU and polymorphic ventricular tachyarrhythmias better known as Torsade de Pointes (TdP). This evidence is briefly examined in this report. The three steps required for the manifestation of EAD-induced triggered activity are: 1) critical prolongation of the repolarization phase, 2) a net depolarizing current carrying the charge for EAD, and 3) propagation of EADs which are locally generated to capture the entire heart resulting in one or more extrasystoles. The majority of pharmaceutical interventions associated with EADs could be grouped as acting predominantly through one of three different mechanisms 1) a delay of one or both potassium currents IK and Ikl, 2) an increase of transsarcolemmal calcium current (ICa), and 3) a delay of sodium current (INa) inactivation. Two experimental models in the dog utilized cesium and anthopleurin-A to produce bradycardia-dependent long QTU and polymorphic ventricular tachyarrhythmias that may resemble the clinical syndrome of long QTU and TdP. In both in vivo models, monophasic action potential (MAP) recordings demonstrated EADs-like deflections more prominent in endocardial than in epicardial recordings. The clinical syndrome of long QTU and TdP can be either congenital, idiopathic or acquired. Several observations suggest a common underlying mechanism with a greater predominance of adrenergic influence in the congenital or idiopathic long QTU syndrome. Adrenergic influence can act by enhancing the depolarizing current of EAD as well as EAD transmission in the intact heart.(ABSTRACT TRUNCATED AT 250 WORDS)