5-Minute Emergency Consult

Qt Syndrome, Prolonged

Qt Syndrome, Prolonged was found in 5-Minute Emergency Consult within Emergency Central. Look up diagnosis tables, treatment guidelines, and drug and disease information.

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Basics

Description

A disorder of myocardial repolarization characterized by a prolonged QT interval on the electrocardiogram
  • 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

Genetics
  • 10 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.
  • 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.

Etiology

  • Drugs:
    • Complete list at http://www.QTDrugs.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
  • Congenital (idiopathic)
  • Other
    • Protein-sparing fasting
    • Anorexia nervosa
    • Hypothyroidism
    • Hypothermia

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