The phenomenon of "qT stunning": The abnormal QT prolongation provoked by standing persists even as the heart rate returns to normal in patients with long QT syndrome

Arnon Adler, Christian Van Der Werf, Pieter G. Postema, Raphael Rosso, Zahir A. Bhuiyan, Jonathan M. Kalman, Jitendra K. Vohra, Milton E. Guevara-Valdivia, Manlio F. Marquez, Amir Halkin, Jesaia Benhorin, Charles Antzelevitch, Arthur A.M. Wilde, Sami Viskin

Research output: Contribution to journalArticlepeer-review

Abstract

Background: Patients with long QT syndrome (LQTS) have inadequate shortening of the QT interval in response to the sudden heart rate accelerations provoked by standing - a phenomenon of diagnostic value. We now validate our original observations in a cohort twice as large. We also describe that this abnormal QT-interval response persists as the heart rate acceleration returns to baseline. Objectives: To describe a novel observation, termed "QT stunning" and to validate previous observations regarding the "QT-stretching" phenomenon in patients with LQTS by using our recently described "standing test." Methods: The electrocardiograms of 108 patients with LQTS and 112 healthy subjects were recorded in the supine position. Subjects were then instructed to stand up quickly and remain standing for 5 minutes during continuous electrocardiographic recording. The corrected QT interval was measured at baseline (QTcbase), when heart rate acceleration without appropriate QT-interval shortening leads to maximal QT stretching (QTcstretch) and upon return of heart rate to baseline (QTcreturn). Results: QTcstretch lengthened significantly more in patients with LQTS (103 ± 80 ms vs 66 ± 40 ms in controls; P <.001) and so did QTcreturn (28 ± 48 ms for patients with LQTS vs -3 ± 32 ms for controls; P <.001). Using a sensitivity cutoff of 90%, the specificity for diagnosing LQTS was 74% for QTc base, 84% for QTcreturn, and 87% for QTc stretch. Conclusions: The present study extends our previous findings on the abnormal response of the QT interval in response to standing in patients with LQTS. Our study also shows that this abnormal response persists even after the heart rate slows back to baseline.

Original languageEnglish
Pages (from-to)901-908
Number of pages8
JournalHeart Rhythm
Volume9
Issue number6
DOIs
StatePublished - Jun 2012

Keywords

  • Electrocardiogram
  • Long QT syndrome
  • QT interval

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