Qt Syndrome, Prolonged
- Alteration in cardiac sodium, potassium, or calcium channel mechanics
- 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.
- 6 genetic loci identified with sporadic cases owing to spontaneous mutations:
- 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
Signs and Symptoms
- Near syncope
- Family history of syncope or sudden death
- Congenital deafness
- Medication use
- QTc (QT corrected for heart rate) >0.44 sec in men and >0.46 sec in women
- QT measured from beginning of quasi-random signal to end of T wave:
- Measured best in the limb leads and should be averaged over 3–5 beats
- There is no expert consensus on best heart rate correction (QTc) formula.
- Bazett formula (QT divided by square root of RR interval) is most commonly used
- Increase in QT variability
- T-wave abnormalities (T-wave alternans, biphasic)
- Appearance of U waves
- Ventricular tachycardia
- Ventricular fibrillation
- Torsades de pointes
Diagnostic Tests and Interpretation
- Full electrolytes including calcium and magnesium
- Toxicology screen
Echocardiography to exclude other cardiac causesDiagnostic Procedures/Other
- ECG stress testing to induce a prolonged QT interval in suspected cases
- Holter monitoring of QTc
- Genetic counseling/testing in suspected congenital forms
- Familial ECG testing
- Myocardial infarction
- Hypertrophic cardiomyopathy
- Valvular defect
- Supplemental oxygen
- IV access
- Stable patients with prolonged QT transported without intervention
- Cardioversion for unstable patients with confirmed torsades de pointes
- Magnesium sulfate for stable patients with evidence of torsades de pointes
- IV access
- Determine hemodynamic stability
- Unstable patients require immediate cardioversion
- IV magnesium sulfate for torsades de pointes
- IV potassium to serum levels of 4.5–5 mEq/L
- Temporary transvenous cardiac pacing (rates from 100–120 beats per min) for recurrences of torsades de pointes refractory to magnesium sulfate therapy (shortens QTc)
- IV isoproterenol for refractory cases or hemodynamically unstable patients with acquired long QT (ineffective in congenital cases) who do not respond to transvenous pacing
- Remove any offending medications and correct metabolic derangements.
- Consult with cardiology in those with symptomatic long QT regarding use of beta blockers at maximum doses.
- No ED treatment needed (in consultation with cardiology) for those with suspected idiopathic long QT and no history of syncope, family history of sudden cardiac death, or ventricular arrhythmias.
- Pacemaker or defibrillator placement with or without cervicothoracic stellectomy (to reduce adrenergic stimulation) may be required in high-risk patients.
- Beta blockers prevent 70% of cardiac events in congenital cases.
- Magnesium sulfate: 2 g (peds: 25–50 mg/kg) IV bolus over 2–3 min followed by IV infusion at 2–4 mg/min
- Isoproterenol: 1μg/min (peds: 0.05–0.1 μg/kg/min) IV continuous infusion, titrate for effect, up to 10 μg/min
Propanolol: 2–3 mg/kg/day (peds: 2–3 mg/kg/day) PO (in consultation with cardiology)
- Symptomatic prolonged QT
- Cardiac dysrhythmia
- Possible cardiac or ischemic event
- Metabolic abnormality
Asymptomatic prolonged QT in consultation with cardiology
Follow-up recommended in all patients with a new diagnosis of prolonged QT
Pearls and Pitfalls
- Suspect prolonged QT in patients with syncope
- Prolonged QT is an independent risk factor for sudden cardiac death.
- Correct electrolyte abnormalities and discontinue offending drugs in those with prolonged QT.
- Magnesium sulfate followed by pacing for torsades de pointes.
- Al-Khatib SM, LaPointe NM, Kramer JM, et al. What clinicians should know about the QT interval. JAMA. 2003;289:2120–127.
- Chugh SS, Reinier K, Singh T, et al. Determinants of prolonged QT interval and their contribution to sudden death risk in coronary artery disease: The Oregon sudden unexpected death study. Circulation. 2009;119:663–670.
- Meyer JS, Mehdirad A, Salem BI, et al. Sudden arrhythmia death syndrome: Importance of the long QT syndrome. Am Fam Physician. 2003;68:483–488.
- Libby P, Bonow RO, Mann DL, Zipes DP, eds. Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine, 8th ed. Philadelphia: Saunders, 2007.
- Zipes DP, Camm AJ, Borggrefe M, et al. ACC/AHA/ESC 2006 Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death-Executive Summary A Report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death). J Am Coll Cardiol. 2006;48:1064.
426.82 Long qt syndrome
- 9651007 long QT syndrome (disorder)
- 442917000 congenital long QT syndrome (disorder)
Jason A. Tracy
© Wolters Kluwer Health Lippincott Williams & Wilkins
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