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Test Findings

QT Prolongation

June 26th, 2019


  • QT Prolongation
A prolonged QT interval represents delayed ventricular repolarisation, and increases the risk of a re-entry circuit from forming (i.e. Torsade de Pointes).
The QT interval is prolonged if it is >450ms in men, >460ms in women, or if there is an increase of >30ms in sequential ECG recordings.
  • Causes of Prolonged QT Interval

  • Congenital

  • Congenital Long QT Syndrome (LQTS)
  • Jervel and Lange-Nielsen syndrome
  • Drugs

  • Antiarrhythmics - amiodarone, sotalol, procainamide, quinidine
  • Antidepressants - amitryptiline, dothiapine, citalopram, escitalopram
  • Antipsychotics - risperidone, haloperidol, clozapine, droperidol, chlorpromazine
  • Antiemetics - ondansetron, domperidone
  • Macrolides - azithromycin, clarithromycin, erythromycin
  • Quinolones - ciprofloxacin, moxifloxacin
  • Antifungals - fluconazole, ketoconazole
  • Antimalarials - chloroquine, mefloquine
  • Anaesthetic gases - halothane, sevoflurane
  • Methadone
  • Other

  • Hypokalaemia
  • Hypomagnesaemia
  • Hypocalcaemia
  • Severe hypothermia
  • Severe bradycardia - sick sinus syndrome, complete heart block
  • Cardiovascular disease - tako-tsubo cardiomyopathy, MI, CCF
  • Cerebrovascular disease - intracranial / subarachnoid haemorrhage, stroke
  • Hypothyroidism
The congenital long QT syndromes are a diverse group of diseases that predispose to ventricular tachyarrhythmias. The three most common are LQTS1, in which events are triggered by exercise; LQTS2, in which events are triggered by stress and loud noises; and LQTS3, in which events often occur during sleep. Other congenital causes are much rarer.
Many drugs can cause a prolonged QT interval; particularly certain antiarrhythmics, many antimicrobials, and many psychoactive drugs.
Electrolyte disturbances can cause prolonged QT intervals, as can severe hypothermia, sevre bradycardia, cardiovascular stress and cerebrovascular pathology.
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