Long QT syndrome (LQTS) is characterized by a prolonged QT interval on ECG, which may be congenital or acquired.
In congenital LQTS, genetic mutations affect ion channels important in myocardial repolarization.
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 characterized 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 17 identified genes result in a variety of channelopathies affecting myocardial repolarization, thus prolonging the QT interval.
Published definitions of the normal QT interval vary. A prolonged QT interval is defined as a heart rate-corrected QT interval (QTc) of >450 ms in males and >460 ms in females. The European Society of Cardiology suggests using a QTc of ≥480 ms for diagnosing LQTS and using a QTc of 460-479 as a borderline range where a diagnosis may be considered along with other criteria.
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 tones
- syncope during arousal or surprise
- arrhythmic symptoms postpartum
- 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 hypokalemia and hypomagnesemia
- ECG for hypocalcemia
- ECG for complete atrioventricular (AV) block
- serum potassium
- serum magnesium
- serum calcium
Investigations to consider
- Holter monitor
- exercise tolerance test
- genetic testing
- epinephrine test
congenital LQTS without previous cardiac event
congenital LQTS with previous cardiac event
- Acquired structural heart disease
- Neurocardiogenic (vasovagal) syncope
- Neurologic syncope
- European Heart Rhythm Association (EHRA)/Heart Rhythm Society (HRS)/Asia Pacific Heart Rhythm Society (APHRS)/Latin American Heart Rhythm Society (LAHRS) Expert Consensus Statement on the state of genetic testing for cardiac diseases
- 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death
Heart attack: what is it?
What you can do to prevent another heart attackMore Patient leaflets
QT Interval CorrectionMore Calculators
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