title: Time- and rate-dependent alterations of the QT interval precede the onset of torsade de pointes in patients with acquired QT prolongation.
abstract: OBJECTIVE
  The purpose of this study was to determine whether the QT interval dynamics that precede torsade de pointes are consistent with the initiation of this arrhythmia by early afterdepolarization-induced triggered activity.
  
  
  BACKGROUND
  Early afterdepolarization-induced triggered activity has been suggested as an electrophysiologic mechanism for torsade de pointes. Consequently, the initiation of torsade de pointes should involve time- and rate-dependent alterations of ventricular repolarization similar to those known to modulate the development of early afterdepolarizations.
  
  
  METHODS
  RR and QT intervals were measured in digitized 24-h ambulatory electrocardiographic recordings obtained from seven patients with acquired prolongation of ventricular repolarization. Each patient had one or more episodes of torsade de pointes. The relation between RR and QT intervals was determined before, during and after multiple episodes of torsade de pointes.
  
  
  RESULTS
  In patients with multiple episodes of ventricular arrhythmias, the onset of the arrhythmias was associated with a critical prolongation of the QT interval. In some episodes, prolongation of the QT interval was associated with sudden prolongation of the sinus cycle length, whereas in other episodes, the QT interval prolonged progressively at a constant cycle length.
  
  
  CONCLUSIONS
  The association between a critically prolonged QT interval and the onset of ventricular arrhythmias suggests that the initial complex of torsade de pointes is an early afterdepolarization-induced triggered response. However, prolongation of the QT interval itself was not sufficient to account for the initiation of torsade de pointes, suggesting that other, as yet unidentified factors are required.
authors.affiliation: Instituto di Clinica Medica Generale e Terapia Medica, Universitá di Milano, Italy. rfg2@cornell.edu
authors.forename: R F
authors.initials: RF
authors.lastname: Gilmour
authors.forename: M L
authors.initials: ML
authors.lastname: Riccio
authors.forename: E H
authors.initials: EH
authors.lastname: Locati
authors.forename: P
authors.initials: P
authors.lastname: Maison-Blanche
authors.forename: P
authors.initials: P
authors.lastname: Coumel
authors.forename: P J
authors.initials: PJ
authors.lastname: Schwartz
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006339:Heart Rate; D006801:Humans; D008133:Long QT Syndrome / Q000150:complications / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D016171:Torsades de Pointes / Q000209:etiology / Q000503:physiopathology*