• Jean-Philippe Couderc, Xiajuan Xia, Derick R Peterson, Scott McNitt, Hongwei Zhao, Slava Polonsky, Arthur J Moss, and Wojciech Zareba.
• Heart Research Follow-Up Program, Cardiology Department, University of Rochester Medical Center, Rochester, New York, USA. jean-philippe.couderc@thew-project.org
• Heart Rhythm. 2011 Jul 1; 8 (7): 1036-43.

BackgroundThere is a consensus on the limited value of the QTc interval prolongation as a surrogate marker of drug cardiotoxicity and as a risk stratifier in inherited long QT syndrome (LQTS) patients.ObjectiveWe investigated the interest of repolarization morphology in the acquired and the inherited LQTS.MethodsWe analyzed 2 retrospective electrocardiographic (ECG) datasets from healthy on/off moxifloxacin and from genotyped KCNH2 patients. We measured QT, RR, and T-peak to T-end intervals, early repolarization duration (ERD) and late repolarization duration, T-roundness, T-amplitude, left (αL) and right slopes of T-waves. We designed multivariate logistic models to predict the presence of the KCNH2 mutation or moxifloxacin while adjusting for the level of QTc prolongation and the level of heart rate in LQT2 patients. Independent learning and validation sets were used. A list of 4,874 ECGs from 411 healthy individuals, 293 from 143 LQT2 carriers and 150 noncarrier family members were analyzed.ResultsIn the moxifloxacin model, ERD was associated with the presence of the drug (odds ratio = 1.15 per ms increase, confidence interval 1.04 to 1.26, P = .0001) after adjustment for QTc. The model for the LQT2 revealed that left slope was associated with the presence of the KCNH2 mutation (odds ratio = 0.38 per 1.5 μV/ms decrease, confidence interval 0.23 to 0.64, P = .0002). Only T-roundness complemented QTc in the model investigating cardiac events in LQT2.ConclusionsThese observations demonstrate that the phenotypic expression of KCNH2 mutations and the effect of IKr-inhibitory drug on the surface electrocardiogram are specific. Future research should investigate whether this phenomenon is linked to different level/form of loss functions of Ikr channels, and whether they could result in different arrhythmogenic mechanisms.Copyright © 2011 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

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