Causes of long QT interval and torsades de pointes
THE CONTEXT
The listed causes include bradycardia, electrolyte disturbances, several drug groups and congenital long QT syndromes.
Bradycardia and electrolyte disturbances
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Bradycardia potentiates other factors that cause torsades de pointes.
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Associated electrolyte disturbances include hypokalaemia, hypomagnesaemia and hypocalcaemia.
Drug causes
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Listed anti-arrhythmic drugs include disopyramide, flecainide and other class Ia or Ic agents, as well as sotalol, amiodarone and other class III agents.
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Other listed groups include amitriptyline and other tricyclic antidepressants, chlorpromazine and other phenothiazines, and erythromycin and other macrolides.
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Hydroxychloroquine and chloroquine are also listed.
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The drug list is not exhaustive; other drugs can also prolong the QT interval.
Congenital syndromes
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Long QT1 involves KCNQ1 and a potassium channel, with a listed proportion of 30%–35%.
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Long QT2 involves HERG and a potassium channel, with a listed proportion of 25%–30%.
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Long QT3 involves SCN5A and a sodium channel, with a listed proportion of 5%–10%.
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Long QT4–12 are rare, with various genes implicated.