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CLINICAL RESEARCH: HEART RHYTHM DISORDER

Giant T–U Waves Precede Torsades de Pointes in Long QT Syndrome

A Systematic Electrocardiographic Analysis in Patients With Acquired and Congenital QT Prolongation

Paulus Kirchhof, MD^_*, Michael R. Franz, MD, PhD^,_*, Abdennasser Bardai, MD and Arthur M. Wilde, MD

^_* VA Medical Center/Georgetown University, Washington, DC
Department of Cardiology and Angiology, University Hospital Münster, and IZKF Münster, Münster, Germany
Heart Failure Research Centre, Department of Cardiology, Academic Medical Centre, Amsterdam, the Netherlands

Manuscript received November 25, 2008; revised manuscript received March 5, 2009, accepted March 10, 2009.

^_* Reprint requests and correspondence: Dr. Michael R. Franz, VA Hospital, Cardiology, 50 Irving Street, NW, Washington, DC 40007 (Email: Michael.r.franz{at}verizon.net).

Objectives: This study sought to identify electrocardiographic (ECG) criteria that are associated with initiation of torsades de pointes (TdP) in patients with acquired (a-) and congenital (c-) long QT syndrome (LQTS).

Background: Electrocardiographic criteria used as risk predictors for TdP commonly rely on a prolonged QT interval but rarely consider abnormal T–U waves.

Methods: We analyzed ECG recordings with TdP from 35 LQTS patients (15 c-LQTS and 20 a-LQTS) and compared them with premature ventricular complexes (PVCs) from 40 patients with normal QT intervals and with PVCs in 24 of the 35 LQTS patients not related to TdP.

Results: Abnormal T–U waves (6.2 ± 0.9 mm) directly preceded TdP in 34 of 35 LQTS patients and were larger than T-wave amplitude (2.8 ± 0.2 mm) in control patients and larger than the largest T–U-wave in LQTS without TdP (4.7 ± 0.8 mm). The TdP-initiating beat emerged from a T–U-wave in 27 of 35 LQTS patients and in none of 40 control patients. The QRS duration of the first TdP beat (175 ± 12 ms) was longer than in control PVCs (145 ± 4 ms) and in PVCs in LQTS patients not related to TdP (138 ± 22 ms). The QRS angle was less steep before TdP than in other PVCs (all p < 0.05).

Conclusions: Abnormal, giant T–U waves separate TdP initiation in LQTS patients from PVCs in other heart disease and from other PVCs in LQTS patients. These ECG analyses suggest that early afterdepolarizations initiate TdP and, if present, may help to identify an imminent risk for TdP.

Key Words: ECG • U-wave • proarrhythmia • torsades de pointes

Abbreviations and Acronyms   a-LQTS = acquired long QT syndrome   c-LQTS = congenital long QT syndrome   EAD = early afterdepolarization   ECG = electrocardiogram   LQTS = long QT syndrome   PVC = premature ventricular complex   TdP = torsades de pointes

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