Long QT Syndrome (see QT (corrected))
also see Hypokalemia

Acquired Causes: Drugs

• Antifungals
• Antiarrhythmics
  • class IA: disopyramide, procainamide, quinidine
  • class III: amiodarone (rare), bretylium, dofetilide, N-acetylprocainamide, sotalol
• Abx: erythromycin, pentamidine, trimethoprim-sulfamethoxazole
• Antidepressants: TCA's
• Antifungals: fluconazole, itraconazole, ketoconazole
• antihistamines: astemizole, terfenadine (removed from market due to this reason)
• antipsychotics: haloperidol, respiridone, phenothiazines such as thioridazine
• Lipid lowering agents (probucol)
• oral hypoglycemics: glibenclamide, glyburide
• organophosphate insecticides
• promotility agents: cisapride

Acquired Causes: Electrolyte Disturbances

• acute hypokalemia (ie diuretics, hyperventilation)
• chronic hypocalcemia, hypokalemia, or hypomagnesemia

Acquired Causes: Underlying medical conditions

• arrythmias: complete AV block, severe bradycardia, sick sinus syndrome
• cardiac: anthracycline toxicity, CHF, myocarditis, tumors
• endocrine: hyperparathyroid, hypothyroid, pheochromocytoma
• neurologic: encephalitis, head trauma, stroke, SAH
• nutritional: alcoholism, anorexia nervosa, liquid protein diet, starvation

Congenital Causes of Long QT syndrome

• Romano-Ward Syndrome (“Romans were dominant”)
  • Autosomal dominant
  • Syncope, seizures, sudden death
  • LQT1 (30% to 50%)--chromosome 11p15.5, K channel
  • LQT2 (20% to 30%)--chromosome 7q35-36, K channel
  • LQT3 (5% to 10%)--chromosome 3p21-24, Na channel
  • LQT4 (?%)--chromosome 4q25-27
  • LQT5 (?%)--chromosome 21q22, K channel
  • LQT6 (?%)--chromosome?
• Jervell and Lange-Nielsen Syndrome
  • Autosomal recessive
  • Sensorineural hearing loss, syncope, seizures, sudden death

EKG: may progress to Torsades de Pointes.

• Torsades de pointes is the pulseless polymorphic tachycardia typically associated with congenital long QT syndromes, but it also can be the fatal arrhythmia associated with profound hypokalemia.
• In many cases of torsades de pointes, hypokalemia is an additive factor that precipitates the arrhythmia in the presence of another predisposing factor.
• Drugs that lead to prolongation of QT include class IA and class IIIantiarrhythmic drugs (e.g., quinidine, amiodarone), high-dose macrolide antibiotics, and cisapride. Ketoconazole and even grapefruit juice inhibit the metabolism of drugs that prolong the QT interval, and thus have also been associated with dangerous prolongation of the QT and arrhythmia when used simultaneously with QT-prolonging drugs.

Treatment

• B-blockers
• Pacemakers, implantable defibrillators
• Avoid medications that may prolong your QT

CHLA Board Review 2005