Qt Syndrome, Prolonged
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DescriptionA 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.
- 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.
- 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.
- 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
- Electrolyte abnormalities
- Arteriovenous block
- Mitral valve prolapse
- Myocardial ischemia
- Subarachnoid hemorrhage
- Congenital (idiopathic)
- Protein-sparing fasting
- Anorexia nervosa