page_title: Long QT syndrome
section_title: Diagnosis
hierarchical_section_title: Long QT syndrome / Diagnosis
caption_attribution_description: English: Adapted from Taggart et. al. (2007) Circulation
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: Diagnosing long QT syndrome is challenging.  Whilst the hallmark of LQTS is prolongation of the QT interval, the QT interval is highly variable among both those who are healthy and those who have LQTS. This leads to overlap between the QT intervals of those with and without LQTS. 2.5% of those with genetically proven LQTS have a QT interval within the normal range.  Conversely, given the normal distribution of QT intervals, a proportion of healthy people will have a longer QT interval than any arbitrary cutoff. Other factors beyond the QT interval should therefore be taken into account when making a diagnosis, some of which have been incorporated into scoring systems.
caption: Range of QT intervals expected in healthy males, healthy females, and those with long QT syndrome.
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