Etiology

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The most common form of congenital LQTS (LQTS type 1) is caused by a defect in the slow delayed rectifier voltage-gated potassium channel.

Acquired LQTS

A prolonged QT interval indicates delayed ventricular de- or repolarization, most commonly caused by drugs (mainly via inhibition of potassium efflux) or electrolyte imbalances.

• Drug-induced LQTS: Usually substances that block potassium outflow during the rapid repolarization phase
  • Macrolides & fluoroquinolones
  • Antiemetics (eg, ondansetron)
  • Azoles (eg, fluconazole)
  • Antipsychotics, TCAs & SSRIs
  • Some opioids (eg, methadone, oxycodone)
  • Class Ia antiarrhythmics (eg, quinidine)
  • Class III antiarrhythmics (eg, dofetilide, sotalol)
• Electrolyte imbalances: hypokalemia, hypomagnesemia, hypocalcemia
• Endocrine disorders: hypothyroidism

Complications

• Ventricular tachycardia (torsades de pointes)
• Ventricular fibrillation
• Asystole
• Sudden cardiac death