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
  • Antiarrhythmics
    • Class Ia (e.g., quinidine, disopyramide, procainamide)
    • Class III (e.g., sotalol; uncommonly, amiodarone)
  • Antibiotics (e.g., macrolides, fluoroquinolones)
  • Antihistamines (e.g., diphenhydramine)
  • Antidepressants (most tricyclic antidepressants and tetracyclic antidepressants, some SSRIs, lithium)
  • Antipsychotics (e.g., haloperidol, ziprasidone)
  • Antiemetics (ondansetron)
  • Antifungals (e.g., azoles)
  • Opioids
  • Protease inhibitors
• Electrolyte imbalances: hypokalemia, hypomagnesemia, hypocalcemia
• Endocrine disorders: hypothyroidism

Complications

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