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Long QT Syndrome

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Overview

Long QT syndrome (LQTS) is a congenital or acquired condition characterised by a prolonged QT interval on an ECG. It is associated with a high risk of cardiac arrest, syncope, and seizures.

Figure 1: An ECG showing long QT syndrome

Epidemiology

  • Affects around 1/2000 people
  • Romano-Ward syndrome is the most common form of inherited LQTS and is autosomal dominant
    • Jervell and Lange-Nielsen syndrome is less common and is an autosomal recessive LQTS

Causes

Genetic

Due to mutations within many genes (around 15):

  • Roman-Ward syndrome
    • Not associated with deafness
  • Jervell and Lange-Nielsen syndrome
    • Associated with sensorineural deafness

Acquired

Drugs:

  • Sotalol
  • Amiodarone
  • Procainamide
  • Tricyclic antidepressants
  • SSRIs, particularly citalopram
  • Macrolide antibiotics, particularly erythromycin and clarithromycin
  • Antihistamines, particularly terfenadine
  • Antipsychotics, such as haloperidol and chlorpromazine
  • Methadone
  • Chloroquine and hydroxychloroquine

Electrolyte imbalances:

  • Hypokalaemia
    • Hyperpolarises myocardial cell membranes leading to prolonged repolarisation and lengthening of the QT interval on an ECG
  • Hypocalcaemia
    • Prolongs the plateau phase of the cardiac action potential and hence prolongs repolarisation of the myocardial cells and lengthens the QT interval on an ECG
  • Hypomagnesaemia
    • Often co-exists with hypokalaemia and leads to early after-depolarisations, prolonging repolarisation of the myocardial cells and lengthening the QT interval on an ECG

Bradyarrhythmia:

Central nervous system (CNS) lesions:

Other:

Risk Factors

  • Family history
  • QT-prolonging drugs
  • Electrolyte imbalances:
    • Hypokalaemia
    • Hypomagnesaemia
    • Hypocalcaemia
  • Bradyarrhythmias
  • CNS lesions

Presentation

  • Syncope:
  • Palpitations
  • Cardiac arrest
  • Syncope during exercise e.g. swimming – associated with LQT1 mutation
  • Syncope during arousal or surprise e.g. surprised by an alarm clock – associated with LQT2 mutation
  • Palpitations post-partum – associated with LQT2 mutation
  • Syncope at rest and during bradycardia – associated with LQT3 mutations

Investigations

All patients

  • ECG:
    • Shows prolonged QT intervals
  • Urea and electrolytes (U&Es), including potassium, magnesium, and calcium
  • Consider Holter monitoring if ECG shows no signs

Management

Overview

  • 1st line: remove/treat causative factors:
    • E.g. removing drugs that cause QT prolongation or correcting electrolyte imbalances
  • Beta-blockers if the causative drug cannot be removed due to medical necessity
    • Avoid sotalol as this can cause QT prolongation
    • Options are: propranolol, metoprolol, nadolol
  • Implantable cardioverter-defibrillator (ICD) in high-risk patients

Complications

Prognosis

  • Patients who are asymptomatic tend to have a better prognosis

Patients who are symptomatic with cardiac arrest have a worse prognosis if there is no early intervention and management

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