Time- and rate-dependent alterations of the QT interval precede the onset of torsade de pointes in patients with acquired QT prolongation

Instituto di Clinica Medica Generale e Terapia Medica, Universita di Milano, Italy. rfg2@cornell.edu

OBJECTIVES: 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.

This article has been cited by other articles:

				K. Ahmad and P. Dorian Drug-induced QT prolongation and proarrhythmia: an inevitable link? Europace, September 1, 2007; 9(suppl_4): iv16 - iv22. [Abstract] [Full Text] [PDF]

				E. T. Locati QT Interval Duration Remains a Major Risk Factor in Long QT Syndrome Patients J. Am. Coll. Cardiol., September 5, 2006; 48(5): 1053 - 1055. [Full Text] [PDF]

				A. A. Fossa, T. Wisialowski, and K. Crimin QT Prolongation Modifies Dynamic Restitution and Hysteresis of the Beat-to-Beat QT-TQ Interval Relationship during Normal Sinus Rhythm under Varying States of Repolarization J. Pharmacol. Exp. Ther., February 1, 2006; 316(2): 498 - 506. [Abstract] [Full Text] [PDF]

				T. V Pham, R. B Robinson, P. Danilo Jr, and M. R Rosen Effects of gonadal steroids on gender-related differences in transmural dispersion of L-type calcium current Cardiovasc Res, February 15, 2002; 53(3): 752 - 762. [Abstract] [Full Text] [PDF]

				T. D. Gbadebo, R. W. Trimble, M. S.C. Khoo, J. Temple, D. M. Roden, and M. E. Anderson Calmodulin Inhibitor W-7 Unmasks a Novel Electrocardiographic Parameter That Predicts Initiation of Torsade de Pointes Circulation, February 12, 2002; 105(6): 770 - 774. [Abstract] [Full Text] [PDF]

				S. G. Priori, R. Bloise, and L. Crotti The long QT syndrome Europace, January 1, 2001; 3(1): 16 - 27. [PDF]

				M. A. Vos, B. Gorenek, S.C. Verduyn, F. F. van der Hulst, J. D. Leunissen, L. Dohmen, and H. J. Wellens Observations on the onset of Torsade de Pointes arrhythmias in the acquired long QT syndrome Cardiovasc Res, December 1, 2000; 48(3): 421 - 429. [Abstract] [Full Text] [PDF]

				M. Zabel, B. Acar, T. Klingenheben, M. R. Franz, S. H. Hohnloser, and M. Malik Analysis of 12-Lead T-Wave Morphology for Risk Stratification After Myocardial Infarction Circulation, September 12, 2000; 102(11): 1252 - 1257. [Abstract] [Full Text] [PDF]