Long QT Syndrome

Describes an ECG where the ventricular repolarization (QT interval) is greatly prolonged

Aetiology

  • Congenital - Jervell–Lange-Nielsen syndrome (autosomal recessive), Romano–Ward syndrome (autosomal dominant)
    • Mutation in ion channel results in reduced/dysfunctional ionic current, prolonging cardiac repolarisation and therefore resulting in QT prolongation
    • Triggers for QT prolongation and torsades de pointes include: potassium-rich foods, diarrhoea, vomiting, underwater breath holding, exercise, sudden auditory stimuli, sleep, QT prolonging states
  • Aquired - includes electrolyte abnormalities, drugs, diabetes and acute MI
    • Drug triggers include β-blockers, psychotropics, analgesics and anesthetics

Clinical presentation

  • Patients with a long QT develop syncope and palpitations as a result of polymorphic ventricular tachycardia (torsades de pointes)
  • They usually terminate spontaneously but may degenerate to ventricular fibrillation, resulting in sudden death

Investigations

ECG

  • Torsades de pointes
  • QT > 0.50 sec
notion image

Management

Acute management of torsades de pointes

  • Treat underlying cause
  • Magnesium infusion
  • Defibrillation if VT occurs

Long term management of congenital QT

  • β-blockers - very effective at reducing sudden cardiac death
  • Avoid QT prolonging drugs and other triggers
  • Pacemarker therapy