Drug-induced early and late proarrhythmia.

Proarrhythmia is the provocation of a new arrhythmia or the exacerbation of a spontaneously occurring arrhythmia due to drug therapy. A drug's toxic effect may occur early after its initiation, and specific definitions have been offered to detect its presence. Primary and secondary forms of proarrhythmia as well as the type of early proarrhythmic events (fatal, serious, and nonserious) have been recognized. More recently, the concept of a late proarrhythmic event (enhanced arrhythmic death) has been defined using placebo-controlled trials. This late proarrhythmic response is extremely important in defining the benefit versus risk ratio that is the key to proper use of drug therapy.