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Long QT Syndrome (LQTS)
Long QT syndrome (LQTS) is a cardiac disorder due to abnormal ion channel function characterized by prolongation of the QT interval on ECG. 75% of cases of LQTS are due to known genetic causes. It is associated with increased risk for syncope (unexplained fainting), ventricular arrhythmia and sudden cardiac death in young adults with normal heart structure. Sudden death is the first and final symptom in 10-15% of individuals with this diagnosis. LQTS has an estimated prevalence greater than 1 in 3000 individuals, occurs in all ethnicities, and results in approximately 4000 deaths annually in the US.
The diagnosis of LQTS is based on clinical history, ECG findings and family history. Typically, the disorder manifests in patients younger than 40 years of age, and sometimes as early as infancy. Patients often have a history of syncope or palpitations in the absence of any other causes, such as medications, structural heart abnormalities, myocardial ischemia, or electrolyte imbalances. The circumstances under which syncope occurs (with exercise, with auditory stimulation, at rest) may further suggest a particular subtype of LQTS. In some patients, syncope may be mistakenly diagnosed as seizures. LQTS may be present even in the absence of any clinical symptoms, and in some patients sudden cardiac death occurs without any preceding symptoms and without an identifiable cause at autopsy. Inherited LQTS may underlie up to 10-15% of sudden infant death syndrome (SIDS) cases.