page_title: Long QT syndrome
section_title: Electrocardiogram
hierarchical_section_title: Long QT syndrome / Diagnosis / Electrocardiogram
caption_attribution_description: English: Cartoons of ECGs showing typical ECG patterns from three commonest forms of inherited Long QT syndrome. LQTS type 1 (LQT1) commonly shows a broad-based T wave pattern, LQTS type 2 (LQT2) shows notched or bifurcated T waves, and LQTS type 3 (LQT3) shows a late-appearing T wave with a prolonged ST segmenAdapted from Farwell and Gollob 2007 Can J Cardiol.
context_page_description: Long QT syndrome is a condition in which repolarization of the heart after a heartbeat is affected. It results in an increased risk of an irregular heartbeat which can result in fainting, drowning, seizures, or sudden death. These episodes can be triggered by exercise or stress. Some rare forms of LQTS are associated with other symptoms and signs including deafness and periods of muscle weakness.
  Long QT syndrome may be present at birth or develop later in life. The inherited form may occur by itself or as part of larger genetic disorder. Onset later in life may result from certain medications, low blood potassium, low blood calcium, or heart failure. Medications that are implicated include certain antiarrhythmics, antibiotics, and antipsychotics. LQTS can be diagnosed using an electrocardiogram if a corrected QT interval of greater than 480–500 milliseconds is found, but clinical findings, other EKG features, and genetic testing may confirm the diagnosis with shorter QT intervals.
  Management may include avoiding strenuous exercise, getting sufficient potassium in the diet, the use of beta blockers, or an implantable cardiac defibrillator.
context_section_description: Long QT syndrome is principally diagnosed by measuring the QT interval corrected for heart rate (QTc) on a 12-lead electrocardiogram (ECG). Long QT syndrome is associated with a prolonged QTc, although in some genetically proven cases of LQTS this prolongation can be hidden, known as concealed LQTS. The QTc is less than 450 ms in 95% of normal males, and less than 460 ms in 95% of normal females. LQTS is suggested if the QTc is longer than these cutoffs.  However, as 5% of normal people also fall into this category, some suggest cutoffs of 470 and 480 ms for males and females respectively, corresponding with the 99th centiles of normal values.
  The major subtypes of inherited LQTS are associated with specific ECG features. LQT1 is typically associated with broad-based T-waves, whereas the T-waves in LQT2 are notched and of lower amplitude, whilst in LQT3 the T-waves are often late onset, being preceded by a long isoelectric segment.
caption: Characteristic ECG patterns associated with the three major subtypes of inherited Long QT syndrome
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