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(Circulation. 2002;106:2473.)
© 2002 American Heart Association, Inc.

Clinical Investigation and Reports

Ambulatory Electrocardiographic Evidence of Transmural Dispersion of Repolarization in Patients With Long-QT Syndrome Type 1 and 2

Matti Viitasalo, MD; Lasse Oikarinen, MD; Heikki Swan, MD; Heikki Väänänen, MSc; Kathy Glatter, MD; Päivi J. Laitinen, MSc; Kimmo Kontula, MD; Hal V. Barron, MD, PhD; Lauri Toivonen, MD; Melvin M. Scheinman, MD

From the Department of Medicine, Cardiac Electrophysiology, University of California, San Francisco (M.V., K.G., H.V.B., M.M.S.); the Department of Medicine, Helsinki University Hospital, Helsinki, Finland (M.V., L.O., H.S., P.J.L., K.K., L.T.); and the Laboratory of Biomedical Engineering, Helsinki University of Technology, Espoo, Finland (H.V.).

Correspondence to Matti Viitasalo, MD, Department of Medicine, Cardiovascular Laboratory, Helsinki University Hospital, Box 340, 00029 HUS, Finland. E-mail matti.viitasalo{at}hus.fi

Background— Transmural dispersion of repolarization (TDR) may be related to the genesis of torsade de pointes (TdP) in patients with the long-QT (LQT) syndrome. Experimentally, LQT2 models show increased TDR compared with LQT1, and ß-adrenergic stimulation increases TDR in both models. Clinically, LQT1 patients experience symptoms at elevated heart rates, but LQT2 patients do so at lower rates. The interval from T-wave peak to T-wave end (TPE interval) is the clinical counterpart of TDR. We explored the relationship of TPE interval to heart rate and to the presence of symptoms in patients with LQT1 and LQT2.

Methods and Results— We reviewed Holter recordings from 90 genotyped subjects, 31 with LQT1, 28 with LQT2, and 31 from unaffected family members, to record TPE intervals by use of an automated computerized program. The median TPE interval was greater in LQT2 (112±5 ms) than LQT1 (91±2 ms) or unaffected (86±3 ms) patients (P<0.001 for all group comparisons), and the maximal TPE values differed as well. LQT1 patients showed abrupt increases in TPE values at RR intervals from 600 to 900 ms, but LQT2 patients did so at RR intervals from 600 to 1400 ms (longest RR studied). Asymptomatic and symptomatic patients showed similar TDRs.

Conclusions— TDR is greater in LQT2 than in LQT1 patients. LQT1 patients showed a capacity to increase TDR at elevated heart rates, but LQT2 patients did so at a much wider rate range. The magnitude of TDR is not related to a history of TdP.

Key Words: arrhythmia • electrocardiography • long-QT syndrome • torsade de pointes

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