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How to measure a QT interval

Kathryn Waddell-Smith, Robert M Gow and Jonathan R Skinner
Med J Aust 2017; 207 (3): 107-110. || doi: 10.5694/mja16.00442

A standard approach in QT measurement improves communication between clinicians

An abnormally prolonged QT interval is associated with an increased risk of sudden cardiac death.1 Some professional bodies recommend national population-based screening programs to detect QT prolongation.2 Familial long QT syndrome (LQTS) may remain undetected because of misdiagnosis (eg, as a seizure disorder)3 or through failure to measure the QT interval correctly.4 Psychiatrists fear the QT prolongation caused by many psychotropic medications,5 and it may also be seen during periods of hypothermia; electrolyte imbalance (such as hypokalaemia, hypomagnesaemia and hypocalcaemia); in the setting of raised intracranial pressure or post-cardiac arrest; with other medications, such as type 1A, 1C and III antiarrhythmic agents; and with antihistamines and macrolide antibiotics.

  • Kathryn Waddell-Smith1
  • Robert M Gow2
  • Jonathan R Skinner1

  • 1 Starship Children's Health, Auckland, New Zealand
  • 2 Children's Hospital of Eastern Ontario, Ottawa, Canada

Correspondence: jskinner@adhb.govt.nz

Competing interests:

Jon Skinner has no relevant disclosures. Kathryn Waddell-Smith is supported by grants from the Green Lane Research and Educational Fund and the National Heart Foundation, New Zealand.

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