I45.81

Long QT syndrome (I45.81): congenital and acquired forms, genetic types, diagnosis and treatment.

Long QT syndrome (LQTS, ICD-10 I45.81) is a disorder of the heart's electrical recovery (repolarisation): the QT interval on the ECG is prolonged. It increases the risk of a dangerous ventricular arrhythmia, torsade de pointes, which can cause palpitations, fainting, seizures or sudden death. The congenital form is caused by variants in genes for cardiac ion channels and affects about 1 in 2000 people. The acquired form, much more common, results from medicines, low potassium, magnesium or calcium, slow heart rate, heart disease or other conditions; often both genetic susceptibility and an acquired trigger act together.

ICD-10 I45.81ChannelopathySudden cardiac death

Congenital LQTS≈ 1 in 2000

Diagnosis (ESC 2022)QTc ≥ 480 ms or LQTS score > 3

High torsade riskQTc > 500 ms

First-line treatmentbeta-blocker

Figure 1. Left: normal QT interval. Right: long QT — the T wave ends much later, prolonging the vulnerable period of repolarisation.

Main genetic types

LQT1 (KCNQ1): events triggered by exercise, especially swimming
LQT2 (KCNH2): events triggered by sudden noise (alarm clock) or emotion, and after childbirth
LQT3 (SCN5A): events during sleep or rest

Diagnosis

LQTS is diagnosed with a QTc of 480 ms or more on repeated ECGs, or with a diagnostic score above 3 that combines ECG, symptoms and family history; genetic testing identifies the type and allows testing of relatives. Holter monitoring, exercise testing and the response of QT to standing help in borderline cases. Every unexplained fainting during exercise or emotion, near-drowning or sudden death in a young relative should prompt an ECG.

Treatment

Beta-blockers (preferably non-selective, such as nadolol or propranolol) for all patients with a diagnosis
Avoid QT-prolonging medicines (lists are available, for example crediblemeds.org), correct potassium and magnesium, and treat vomiting and diarrhoea promptly
For high-risk patients: implantable cardioverter-defibrillator (ICD), left cardiac sympathetic denervation; mexiletine in LQT3
Acquired LQTS: stop the offending drug, correct electrolytes; in torsade de pointes give intravenous magnesium

Call emergency services

for fainting, seizures or palpitations in a person with long QT, especially after starting a new medicine or with vomiting or diarrhoea.

References

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;43(40):3997–4126. doi:10.1093/eurheartj/ehac262
Schwartz PJ, Stramba-Badiale M, Crotti L, et al. Prevalence of the congenital long-QT syndrome. Circulation. 2009;120(18):1761–1767. doi:10.1161/CIRCULATIONAHA.109.863209
Drew BJ, Ackerman MJ, Funk M, et al. Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation. Circulation. 2010;121(8):1047–1060. doi:10.1161/CIRCULATIONAHA.109.192704

This article is for general information and does not replace a consultation with a doctor. Diagnosis and treatment must be decided by a physician on the basis of symptoms, examination and tests.

Published on 23 March 2019

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