Qt Syndrome, Prolonged



A disorder of myocardial repolarization characterized by a prolonged QT interval on the ECG
  • The pathophysiology is complex and incompletely understood:
    • Alteration in cardiac sodium, potassium, or calcium ion flow
    • Imbalance in the sympathetic innervation of the heart
  • Prolonged ventricular repolarization results in lengthening of QT interval on surface ECG:
    • “Pause-dependent” lengthening due to short–long–short sequence in which a sinus beat is followed by an extrasystole (short), then a postextrasystolic pause (long), concluding with a ventricular extrasystole (short)
    • “Adrenergic-dependent” pauses found in congenital cases
  • Symptoms often preceded by vigorous exercise, emotional stress, or loud noise
  • Nocturnal bradycardia can lengthen QT interval, causing sleep-related symptoms
  • Re-entrant rhythm can lead to torsades de pointes, ventricular tachycardia, and ventricular fibrillation
  • Hemodynamic compromise following dysrhythmia leads to syncope or death
  • Independent risk factor for sudden cardiac death

Risk Factors

  • 20 genes linked to long QT syndrome:
    • Autosomal recessive form associated with deafness (Jervell and Lange–Nielsen syndromes)
    • Autosomal dominant form not associated with deafness (Romano–Ward syndrome)
    • Adrenergic stimulation (fright, exertion, delirium tremens, and loud auditory stimulus) becomes prodysrhythmic in certain genotypes, while sleep-related symptoms are found in others
  • 10–15% of carriers have baseline normal QTc
  • Specific genetic mutations increase risk of cardiac events
  • Death occurs in 1–2% of untreated patients per year
    • Drug-induced QT prolongation may also have a genetic background
    • Congenital form occurs in 1 in 3,000–5,000, with mortality of 6% by age 40 yr

Pediatric Considerations
  • Diagnosis suspected in the young with syncope, cardiac arrest, or sudden death
  • Syncope following emotional stress or exercise suggestive
  • Death occurs without preceding symptoms in 10% of pediatric patients


  • Drugs:
    • Complete list at http://www.crediblemeds.org
    • Class Ia antidysrhythmics – quinidine, procainamide, disopyramide
    • Class III antidysrhythmics – sotalol, ibutilide, amiodarone
    • Antibiotics – erythromycin, pentamidine, chloroquine, trimethoprim–sulfamethoxazole
    • Antifungal agents – ketoconazole, itraconazole
    • Psychotropic drugs – phenothiazines, haloperidol, risperidone, STCAs
    • Cisapride
    • Antihistamines
    • Organophosphates
    • Narcotics – methadone
  • Electrolyte abnormalities:
    • Hypokalemia
    • Hypomagnesemia
    • Hypocalcemia
  • Cardiac:
    • Bradyarrhythmias
    • Arteriovenous block
    • Mitral valve prolapse
    • Myocarditis
    • Myocardial ischemia
  • CNS:
    • Subarachnoid hemorrhage
    • Stroke
    • Raised intracranial pressure
  • Congenital (idiopathic)
  • Other
    • Protein-sparing fasting
    • Anorexia nervosa
    • Hypothyroidism
    • Hypothermia

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