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CLINICAL RESEARCH: HEART RHYTHM DISORDER

Ratio of Late to Early T-Wave Peak Amplitude in 24-h Electrocardiographic Recordings as Indicator of Symptom History in Patients With Long-QT Syndrome Types 1 and 2

Matti Viitasalo, MD^_*,_*, Lasse Oikarinen, MD^_*, Heikki Swan, MD^_*, Kathryn A. Glatter, MD, Heikki Väänänen, MSc, Heidi Fodstad, MSc, Nipavan Chiamvimonvat, MD, Kimmo Kontula, MD, Lauri Toivonen, MD, FACC^_* and Melvin M. Scheinman, MD, FACC^||

^_* Department of Cardiology, Helsinki University Central Hospital, Helsinki, Finland
Department of Medicine, Helsinki University Central Hospital, Helsinki, Finland
Department of Cardiology, University of California, Davis, California
Laboratory of Biomedical Engineering, Helsinki University of Technology, Espoo, Finland
^|| Department of Medicine, Cardiac Electrophysiology, University of California, San Francisco, California

Manuscript received April 16, 2005; revised manuscript received July 14, 2005, accepted July 25, 2005.

^_* Reprint requests and correspondence: Dr. Matti Viitasalo, Department of Cardiology, University Central Hospital, Haartmaninkatu 4, 00290 Helsinki, Finland. (Email: matti.viitasalo{at}hus.fi).

OBJECTIVES: We tested the hypothesis that in long-QT syndrome types 1 (LQT1) and 2 (LQT2), the diurnal maximal ratio between late and early T-wave peak amplitudes correlates with a history of symptoms better than QT interval durations.

BACKGROUND: Genotype and phenotype studies have delineated clinical profiles of the most prevalent LQT1 and LQT2 subtypes of inherited LQT, but prediction of arrhythmia risk remains uncertain, the baseline QTc interval being the best predictor. In experimental long-QT syndrome models, the ratio between late and early T-wave peak amplitude predicts onset of torsade de pointes.

METHODS: We reviewed 24-h electrocardiographic recordings from 214 genotyped subjects—97 with LQT1, 62 with LQT2, and 55 unaffected—to record maximal amplitude ratios between late and early T-wave peaks by use of a computer-assisted program.

RESULTS: Maximal amplitude ratios between late and early T-wave peaks were higher in symptomatic than in asymptomatic patients both in LQT1 (3.2 ± 1.0 vs. 2.3 ± 0.8; p < 0.001) and LQT2 patients (2.6 ± 1.0 vs. 1.7 ± 0.5; p < 0.001). Although the QTc interval also was longer in symptomatic patients, only the maximal amplitude ratio between late and early T-wave peaks was independently associated with symptoms in both LQT1 and LQT2 patients.

CONCLUSIONS: Maximal diurnal ratio between late and early T-wave peak amplitude improves noninvasive risk assessment both in LQT1 and LQT2 syndromes. We propose this new indicator in clinical evaluation of arrhythmia risk in LQT1 and LQT2.

Abbreviations and Acronyms   ECG = electrocardiogram/electrocardiographic   LQT = long-QT syndrome   LQT1 = long-QT syndrome type 1   LQT2 = long-QT syndrome type 2   TdP = torsades de pointes

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