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EXPEDITED PUBLICATION

The Response of the QT Interval to the Brief Tachycardia Provoked by Standing

A Bedside Test for Diagnosing Long QT Syndrome

Sami Viskin, MD^_*,_*, Pieter G. Postema, MD, Zahurul A. Bhuiyan, MD, PhD, Raphael Rosso, MD^||, Jonathan M. Kalman, MBBS, PhD^||, Jitendra K. Vohra, MD^||, Milton E. Guevara-Valdivia, MD^¶, Manlio F. Marquez, MD^#, Evgeni Kogan, MD^_*, Bernard Belhassen, MD^_*, Michael Glikson, MD, Boris Strasberg, MD, Charles Antzelevitch, PhD^{_{* *}} and Arthur A.M. Wilde, MD

^_* Tel-Aviv
Sheva
Rabin Medical Centers, Tel Aviv University, Tel Aviv, Israel
Academic Medical Center, Amsterdam, the Netherlands
^|| Royal Melbourne Hospital, University of Melbourne, Melbourne, Australia
^¶ UMAE Hospital Dr. Antonio Fraga-Mouret CMN La-Raza IMSS
^# Instituto Nacional de Cardiologia, Mexico City, Mexico
^_** Masonic Medical Research Laboratory, Utica, New York. Financial support is provided by the Netherlands Heart Foundation Grant 2005T024 (Dr. Postema)

Manuscript received October 25, 2009; revised manuscript received December 7, 2009, accepted December 21, 2009.

^_* Reprint requests and correspondence: Dr. Sami Viskin, Department of Cardiology, Tel-Aviv Medical Center, Weizman 6, Tel-Aviv 64239, Israel (Email: saviskin{at}tasmc.health.gov.il).

Objectives: This study was undertaken to determine whether the short-lived sinus tachycardia that occurs during standing will expose changes in the QT interval that are of diagnostic value.

Background: The QT interval shortens during heart rate acceleration, but this response is not instantaneous. We tested whether the transient, sudden sinus tachycardia that occurs during standing would expose abnormal QT interval prolongation in patients with long QT syndrome (LQTS).

Methods: Patients (68 with LQTS [LQT1 46%, LQT2 41%, LQT3 4%, not genotyped 9%] and 82 control subjects) underwent a baseline electrocardiogram (ECG) while resting in the supine position and were then asked to get up quickly and stand still during continuous ECG recording. The QT interval was studied at baseline and during maximal sinus tachycardia, maximal QT interval prolongation, and maximal QT interval stretching.

Results: In response to brisk standing, patients and control subjects responded with similar heart rate acceleration of 28 ± 10 beats/min (p = 0.261). However, the response of the QT interval to this tachycardia differed: on average, the QT interval of controls shortened by 21 ± 19 ms whereas the QT interval of LQTS patients increased by 4 ± 34 ms (p < 0.001). Since the RR interval shortened more than the QT interval, during maximal tachycardia the corrected QT interval increased by 50 ± 30 ms in the control group and by 89 ± 47 ms in the LQTS group (p < 0.001). Receiver-operating characteristic curves showed that the test adds diagnostic value. The response of the QT interval to brisk standing was particularly impaired in patients with LQT2.

Conclusions: Evaluation of the response of the QT interval to the brisk tachycardia induced by standing provides important information that aids in the diagnosis of LQTS.

Key Words: long QT syndrome • electrocardiogram • QT interval

Abbreviations and Acronyms   AUC = area under the curve   ECG = electrocardiogram   IQR = interquartile range   LQTS = long QT syndrome   ROC = receiver-operating characteristic

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