Long QT syndrome (LQTS) is characterised by a prolonged QT interval on ECG, which may be congenital or acquired.
In congenital LQTS, genetic mutations affect ion channels important in myocardial repolarisation.
Acquired LQTS may occur secondary to ingestion of QT interval-prolonging drugs, electrolyte imbalances, or bradyarrhythmias.
Patients with LQTS are at increased risk of syncope, ventricular arrhythmias (including torsades de pointes), and sudden cardiac death.
Unless there is an identifiable reversible cause, treatment primarily involves lifestyle modification and beta-blocker therapy with the implantation of a cardioverter-defibrillator in selected cases.
Long QT syndrome (LQTS) is a congenital or acquired condition that is characterised by a prolonged QT interval on the surface ECG and is associated with a high risk of sudden cardiac death due to ventricular tachyarrhythmias. In congenital LQTS, mutations within 15 identified genes result in a variety of channelopathies affecting myocardial repolarisation, thus prolonging the QT interval.
History and exam
Key diagnostic factors
- history of known gene mutation
- use of drugs or circumstances known to increase the QT interval
- syncope during heightened adrenergic tone
- syncope during arousal or surprise
- arrhythmic symptoms post partum
- syncope at rest and during bradycardia
- cardiac syncope
- periodic paralysis
- dysmorphic features
- sensorineural deafness
Other diagnostic factors
- muscle weakness
- Chvostek's sign
- Trousseau's sign
- cold and pale extremities
- KCNQ1 gene mutations
- KCNH2 gene mutations
- SCN5A gene mutations
- QT interval-prolonging drugs
- central nervous system lesions
- female sex
1st investigations to order
- ECG for LQT1
- ECG for LQT2
- ECG for LQT3
- ECG for hypokalaemia and hypomagnesaemia
- ECG for hypocalcaemia
- ECG for complete atrioventricular (AV) block
- serum potassium
- serum magnesium
- serum calcium
Investigations to consider
- Holter monitor
- exercise tolerance test
- genetic testing
- adrenaline (epinephrine) test
acquired LQTS without previous cardiac event
congenital LQTS without previous cardiac event
acquired LQTS with previous cardiac event
congenital LQTS with previous cardiac event
Mehmet K. Aktas, MD, MBA
Associate Professor of Medicine
University of Rochester Medical Center
MKA declares that he has received research support from Medtronic and Biosense Webster. He is the author of a reference cited in this topic.
James P. Daubert, MD
Professor of Medicine
Duke University Medical Center
Duke Clinical Research Institute
JPD declares that he has received honoraria for advisory boards, data safety monitoring boards, events committees, or lecture fees from Abbott, Biosense Webster, Biotronik, Boston Scientific, Farapulse, Gilead Sciences Inc., Medtronic, Microport, Phillips, Vytronus, and ZOLL; and research grants from Abbott and Medtronic. JPD declares that he has no stock, stock options, or other forms of ownership. He is the author of a reference cited in this topic.
Sami Viskin, MD
Director of Cardiac Hospitalization
Department of Cardiology
Tel Aviv Medical Center
SV declares that he has no competing interests.
Elizabeth S. Kaufman, MD
Heart and Vascular Center
Case Western Reserve University
ESK declares that she has no competing interests.
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- Guidelines for the diagnosis and management of syncope
- 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death
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