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Test Findings
Test Findings

QT Prolongation



    • 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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