Peer Reviewed
ECG education

Is this a prolonged QT interval?

Vivienne Miller
Abstract
Juana, aged 52 years, has been advised to find herself a GP. She presents to you with a discharge referral from a psychiatric unit stating she has longstanding schizophrenia and depression and is taking clozapine 400 mg/day and fluoxetine 20 mg/day. She has been otherwise medically well, except for a recurrent tooth abscess. An ECG has not been documented as being conducted in hospital, so you arrange one.
Key Points
  • The QT interval varies with heart rate.
  • It lengthens with slower heart rates and shortens with faster heart rates.
  • Prolonged QT intervals occur much more commonly in women than men.
  • A QT interval of 500 ms is always long and 430 to 450 ms is often long.
  • An ECG is the usual diagnostic investigation.
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