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EXPEDITED REVIEW

Corrected QT Variability in Serial Electrocardiograms in Long QT Syndrome

The Importance of the Maximum Corrected QT for Risk Stratification

Ilan Goldenberg, MD^_*,_*, Jehu Mathew, BS^_*, Arthur J. Moss, MD^_*, Scott McNitt, MS^_*, Derick R. Peterson, PhD, Wojciech Zareba, MD, PhD^_*, Jesaia Benhorin, MD, Li Zhang, MD, G. Michael Vincent, MD, FACC^,||, Mark L. Andrews, BBS^_*, Jennifer L. Robinson, MS^_* and Brian Morray, BS^_*

^_* Cardiology Division, Department of Medicine, University of Rochester Medical Center, Rochester, New York
Department of Biostatistics and Computational Biology, University of Rochester Medical Center, Rochester, New York
Bikur Cholim Hospital, University of Jerusalem, Jerusalem, Israel
Latter Day Saints Hospital, Salt Lake City, Utah
^|| University of Utah School of Medicine, Salt Lake City, Utah.

Manuscript received January 6, 2006; revised manuscript received February 13, 2006, accepted March 6, 2006.

^_* Reprint requests and correspondence: Dr. Ilan Goldenberg, Heart Research Follow-Up Program, Box 653, University of Rochester Medical Center, Rochester, New York 14642. (Email: ilan.goldenberg{at}heart.rochester.edu).

OBJECTIVES: We evaluated the incremental prognostic information provided by multiple corrected QT (QTc) measurements on serial electrocardiograms (ECGs) in patients with the inherited long QT syndrome (LQTS).

BACKGROUND: A baseline QTc of 500 ms has been shown to be associated with increased risk of cardiac events among LQTS patients. However, the value of QTc measurements on follow-up ECGs in risk assessment has not been determined.

METHODS: The risk of a first LQTS-related cardiac event during adolescence was assessed in 375 patients enrolled in the International LQTS Registry for whom serial follow-up ECGs were recorded before age 10.

RESULTS: The mean ± SD difference between the minimum and maximum QTc values on serial ECGs recorded in study patients was 47 ± 40 ms. The maximum QTc interval recorded before age 10 was the strongest predictor of cardiac events during adolescence (adjusted hazard ratio [HR] = 2.74; p < 0.001). Other follow-up QTc measures, including the baseline, the mean, and the most recent QTc interval recorded before age 10, were less significant risk factors. After adjusting for the maximum QTc value during follow-up, no significant association remained between the baseline QTc value and the risk of subsequent cardiac events (HR = 1.04; p = 0.91).

CONCLUSIONS: In LQTS patients, there is a considerable variability in QTc measures in serial follow-up ECGs. The maximum QTc interval provides incremental prognostic information beyond the baseline measurement. We suggest that risk stratification in LQTS patients should include follow-up ECG data.

Abbreviations and Acronyms   ACA = aborted cardiac arrest   ECG = electrocardiogram   HR = hazard ratio   LQTS = long QT syndrome   QTc = corrected QT

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