THE QT INTERVAL AND DRUG-ASSOCIATED TORSADES-DE-POINTES

Torsades de pointes is an uncommon form of ventricular tachyarrhythmia, which may occur in the presence or absence of drug therapy. There are several difficulties in establishing a relationship between drug therapy and the induction of this arrhythmia. Drugs for which a definitive association with torsades de pointes are established, i.e. class IA and III antiarrhythmics, are known to prolong the QT or QT(c) interval. However, the definition of significant QT or QT(c) prolongation is sometimes difficult because there is a significant inter- and intrapatient variability in the observed QT or QT(c) interval even in the absence of drug therapy. Furthermore, some drugs that induce prolongation of the QT or QT(c) interval in a given patient do not precipitate torsades de pointes. Recent reports of unexpected drug-induced torsades de pointes by drugs other than class IA or III antiarrhythmics led to the examination of the association between QT interval prolongation and torsades de pointes, and evaluation of the mechanisms for drug-induced torsades de pointes by drugs other than class IA or III antiarrhythmic drugs.