Which clinical history is characteristic of long QT syndrome (LQTS)?

Updated: Nov 29, 2017
  • Author: Ali A Sovari, MD, FACP, FACC; Chief Editor: Mikhael F El-Chami, MD  more...
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A history of cardiac events is the most typical clinical presentation in patients with long QT syndrome (LQTS). LQTS is usually diagnosed after a person has a cardiac event (eg, syncope, cardiac arrest). In some situations, LQTS is diagnosed after a family member suddenly dies. In some individuals, LQTS is diagnosed because an electrocardiogram (ECG) shows QT prolongation.

Exercise, swimming, or emotion may trigger events, but they may also occur during night sleep.

Triggering events are somewhat different by genotype. Patients with LQT1 usually have cardiac events preceded by exercise or swimming. Sudden exposure of the patient's face to cold water is thought to elicit a vagotonic reflex. Patients with LQT2 may have arrhythmic events after an emotional event, exercise, or exposure to auditory stimuli (eg, door bells, telephone ring). Patients with LQT3 usually have events during night sleep.

Obtain information about hearing loss (deficit) in patients and their family members to determine a possibility of Jervell and Lang-Nielsen (JLN) syndrome.

Information about what medication the patient has taken is critical for the differential diagnosis of congenital LQTS and of drug-induced QT prolongation (which also may have genetic background). The Arizona Center for Education and Research on Therapeutics (AZCERT) provides lists of drugs that prolong the QT interval and/or induce torsade de pointes ventricular arrhythmia.

A family history of cardiac arrest and sudden death, especially at a young age, may suggest a congenital (familial) form of LQTS.

Analysis of repolarization duration (QTc) and morphology on the patient's ECG and on ECGs of the patient's relatives frequently leads to the proper diagnosis.

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