Long QT syndrome

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Last reviewed: 5 Jun 2025

Last updated: 29 Aug 2023

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.

Definition

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 17 identified genes result in a variety of channelopathies affecting myocardial repolarisation, 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.[1]Rautaharju PM, Surawicz B, Gettes LS, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: endorsed by the International Society for Computerized Electrocardiology. Circulation. 2009 Mar 17;119(10):e241-50. 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.[2]

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 postnatal
syncope at rest and during bradycardia
cardiac syncope
palpitations
periodic paralysis
dysmorphic features
sensorineural deafness

Full details

Other diagnostic factors

dizziness
angina
fatigue
oliguria
muscle weakness
tetany
numbness
Chvostek's sign
Trousseau's sign
cold and pale extremities
hypotension
confusion

Full details

Risk factors

KCNQ1 gene mutations
KCNH2 gene mutations
SCN5A gene mutations
QT interval-prolonging drugs
hypokalaemia
hypomagnesaemia
hypocalcaemia
bradyarrhythmias
central nervous system lesions
female sex
malnutrition

Full details

Diagnostic investigations

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

Full details

Investigations to consider

Holter monitor
exercise tolerance test
echocardiography
genetic testing
adrenaline (epinephrine) test

Full details

Treatment algorithm

ACUTE

acquired LQTS

congenital LQTS without previous cardiac event

congenital LQTS with previous cardiac event

Contributors

Authors

Mehmet K. Aktas, MD, MBA

Associate Professor of Medicine

University of Rochester Medical Center

Rochester

Disclosures

MKA declares that he has received research grants from Astra Zeneca, Medtronic, and Boston Scientific. MKA has served as consultant for Abbott and Huxley Medical. MKA holds a patent for ‘ECG Clock Electrocardiogram Based Diagnostic Device and Method’ (US patent #10,085,667). 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

Durham

Disclosures

JPD declares that he has received honoraria for advisory boards, steering committees, data safety monitoring boards, events committees, and lecture fees from Abbott, Acutus Medical, Affera Inc., Biosense Webster, Biotronik, Boston Scientific, Farapulse, Gilead Sciences Inc., Medtronic, Microport, Phillips, and Vytronus; and research grants from Abbott, Biosense Webster, Boston Scientific, Farapulse, and Medtronic. He receives royalty payments from Wiley, Springboard and McGraw Hill for textbook authorship and educational materials. 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.

Peer reviewers

Sami Viskin, MD

Director of Cardiac Hospitalization

Department of Cardiology

Tel Aviv Medical Center

Tel Aviv

Israel

Disclosures

SV declares that he has no competing interests.

Elizabeth S. Kaufman, MD

Associate Professor

Heart and Vascular Center

MetroHealth Campus

Case Western Reserve University

Cleveland

Disclosures

ESK declares that she has no competing interests.

References

Our in-house evidence and editorial teams collaborate with international expert contributors and peer reviewers to ensure that we provide access to the most clinically relevant information possible.

Key articles

Zeppenfeld K, Tfelt-Hansen J, de Riva M, et al. 2022 ESC guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J. 2022 Oct 21;43(40):3997-4126.Full text Abstract

Priori SG, Wilde AA, Horie M, et al. HRS/EHRA/APHRS expert consensus statement on the diagnosis and management of patients with inherited primary arrhythmia syndromes. Heart Rhythm. 2013 Dec;10(12):1932-63.Full text Abstract

Wilde AAM, Semsarian C, Márquez MF, et al. 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. Europace. 2022 Sep 1;24(8):1307-67.Full text Abstract

Roden DM. Clinical practice. Long-QT syndrome. N Engl J Med. 2008 Jan 10;358(2):169-76. Abstract

Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: a report of the American College of Cardiology/American Heart Association Task Force on clinical practice guidelines and the Heart Rhythm Society. Circulation. 2018 Sep 25;138(13):e272-391.Full text Abstract

Sauer AJ, Moss AJ, McNitt S, et al. Long QT syndrome in adults. J Am Coll Cardiol. 2007 Jan 23;49(3):329-37. Abstract

Schwartz PJ, Moss AJ, Vincent GM, et al. Diagnostic criteria for the long QT syndrome. An update. Circulation. 1993 Aug;88(2):782-4. Abstract

Schwartz PJ, Crotti L. QTc behavior during exercise and genetic testing for the long-QT syndrome. Circulation. 2011 Nov 15;124(20):2181-4.Full text Abstract

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials
- Acquired structural heart disease
- Neurocardiogenic (vasovagal) syncope
- Neurological syncope
More Differentials
Guidelines
- 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
More Guidelines
Patient information
Heart attack: what is it?
What you can do to prevent another heart attack
More Patient information
Calculators
QT Interval Correction
More Calculators
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Long QT syndrome

Summary

Definition

History and exam

Key diagnostic factors

Other diagnostic factors

Risk factors

Diagnostic investigations

1st investigations to order

Investigations to consider

Treatment algorithm

acquired LQTS

congenital LQTS without previous cardiac event

congenital LQTS with previous cardiac event

Contributors

Authors

Mehmet K. Aktas, MD, MBA

Disclosures

James P. Daubert, MD

Disclosures

Peer reviewers

Sami Viskin, MD

Disclosures

Elizabeth S. Kaufman, MD

Disclosures

References

Key articles

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials

Guidelines

Patient information

Calculators

Log in or subscribe to access all of BMJ Best Practice

Log in or subscribe to access all of BMJ Best Practice

Log in to access all of BMJ Best Practice