Long QT syndrome

Long QT syndrome (LQTS) is a condition affecting repolarization (relaxing) of the heart after a heartbeat, giving rise to an abnormally lengthy QT interval.^[7] It results in an increased risk of an irregular heartbeat which can result in fainting, drowning, seizures, or sudden death.^[1] These episodes can be triggered by exercise or stress.^[6] Some rare forms of LQTS are associated with other symptoms and signs including deafness and periods of muscle weakness.^[1]

Long QT syndrome may be present at birth or develop later in life.^[1] The inherited form may occur by itself or as part of larger genetic disorder.^[1] Onset later in life may result from certain medications, low blood potassium, low blood calcium, or heart failure.^[2] Medications that are implicated include certain antiarrhythmics, antibiotics, and antipsychotics.^[2] LQTS can be diagnosed using an electrocardiogram (EKG) if a corrected QT interval of greater than 450–500 milliseconds is found, but clinical findings, other EKG features, and genetic testing may confirm the diagnosis with shorter QT intervals.^[4][5][8]

Management may include avoiding strenuous exercise, getting sufficient potassium in the diet, the use of beta blockers, or an implantable cardiac defibrillator.^[6] For people with LQTS who survive cardiac arrest and remain untreated, the risk of death within 15 years is greater than 50%.^[9][6] With proper treatment this decreases to less than 1% over 20 years.^[3]

Long QT syndrome is estimated to affect 1 in 7,000 people.^[6] Females are affected more often than males.^[6] Most people with the condition develop symptoms before they are 40 years old.^[6] It is a relatively common cause of sudden death along with Brugada syndrome and arrhythmogenic right ventricular dysplasia.^[3] In the United States it results in about 3,500 deaths a year.^[6] The condition was first clearly described in 1957.^[10]