"QT clock" to improve detection of QT prolongation in long QT syndrome patients

Heart Rhythm. 2016 Jan;13(1):190-8. doi: 10.1016/j.hrthm.2015.08.037. Epub 2015 Aug 31.


Background: The QT interval is a risk marker for cardiac events such as torsades de pointes. However, QT measurements obtained from a 12-lead ECG during clinic hours may not capture the full extent of a patient's daily QT range.

Objective: The purpose of this study was to evaluate the utility of 24-hour Holter ECG recording in patients with long QT syndrome (LQTS) to identify dynamic changes in the heart rate-corrected QT interval and to investigate methods of visualizing the resulting datasets.

Methods: Beat-to-beat QTc (Bazett) intervals were automatically measured across 24-hour Holter recordings from 202 LQTS type 1, 89 type 2, and 14 type 3 genotyped patients and a reference group of 200 healthy individuals. We measured the percentage of beats with QTc greater than the gender-specific threshold (QTc ≥470 ms in women and QTc ≥450 ms in men). The percentage of beats with QTc prolongation was determined across the 24-hour recordings.

Results: Based on the median percentage of heartbeats per patient with QTc prolongation, LQTS type 1 patients showed more frequent QTc prolongation during the day (~3 PM) than they did at night (~3 AM): 97% vs 48%, P ~10(-4) for men, and 68% vs 30%, P ~10(-5) for women. LQTS type 2 patients showed less frequent QTc prolongation during the day compared to nighttime: 87% vs 100%, P ~10(-4) for men, and 62% vs 100%, P ~10(-3) for women.

Conclusion: In patients with genotype-positive LQTS, significant differences exist in the degree of daytime and nocturnal QTc prolongation. Holter monitoring using the "QT clock" concept may provide an easy, fast, and accurate method for assessing the true personalized burden of QTc prolongation.

Keywords: Cardiac monitoring; Diagnostic; Electrocardiography; Long QT syndrome.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adolescent
  • Adrenergic beta-Antagonists / therapeutic use*
  • Adult
  • Child
  • Child, Preschool
  • ERG1 Potassium Channel
  • Electrocardiography, Ambulatory / methods*
  • Ether-A-Go-Go Potassium Channels / genetics
  • Female
  • Heart Rate / drug effects
  • Humans
  • KCNQ1 Potassium Channel / genetics
  • Long QT Syndrome* / diagnosis
  • Long QT Syndrome* / drug therapy
  • Long QT Syndrome* / genetics
  • Long QT Syndrome* / physiopathology
  • Male
  • Reproducibility of Results
  • Risk Assessment / methods
  • Risk Factors
  • Romano-Ward Syndrome* / diagnosis
  • Romano-Ward Syndrome* / drug therapy
  • Romano-Ward Syndrome* / genetics
  • Romano-Ward Syndrome* / physiopathology
  • Sex Factors
  • Time Factors


  • Adrenergic beta-Antagonists
  • ERG1 Potassium Channel
  • Ether-A-Go-Go Potassium Channels
  • KCNQ1 Potassium Channel
  • KCNQ1 protein, human

Supplementary concepts

  • Long Qt Syndrome 2
  • Long Qt Syndrome 3