Long QT syndrome is a hereditary or acquired disorder characterized by abnormal prolongation of the corrected QT (QTc) interval on the electrocardiogram and a predisposition to life-threatening arrhythmias such as torsades de pointes. This condition is caused by impaired ventricular myocardial repolarization, which creates conditions for the occurrence of early postdepolarizations and trigger activity. The pathophysiological basis of the syndrome is dysfunction of ion channels, primarily potassium, sodium and calcium, which regulate the transmembrane ion current in cardiomyocytes.
History of the disease and interesting historical facts
The first descriptions of sudden cardiac death in young people without visible structural changes in the heart appeared in the early 20th century. However, the official discovery of the syndrome is associated with the work of French researchers Francois Romano and Lucien Coumel in the 1950s. Of particular interest is the case of the Jervell and Lange-Nielsen family, described in 1957, where a link was found between congenital deafness and prolongation of the QT interval. According to the Framingham Heart Study, the first systematic observations of patients with prolonged QT showed a significant increase in the risk of sudden cardiac death.
Epidemiology
According to modern epidemiological studies, the prevalence of congenital long QT syndrome is approximately 1 case per 2000-2500 newborns. At the same time, the ratio of men to women among patients is approximately 1:1.3, which indicates a higher predisposition of the female sex to this condition. According to a 2020 meta-analysis conducted by the European Heart Rhythm Association, the mortality rate among untreated patients reaches 50% within 10 years after diagnosis. It is important to note that about 10-15% cases of sudden cardiac death in young people may be associated with this syndrome.
Genetic predisposition to this disease
The genetic form of the syndrome is based on mutations in genes encoding proteins of cardiac ion channels:
- KCNQ1 (LQT1) - mutations in this gene account for up to 30-35% of all cases
- KCNH2 (LQT2) - responsible for 25-30% cases
- SCN5A (LQT3) - detected in 5-10% cases
- Other genes (KCNJ2, CACNA1C, etc.) - less than 5%
"The most common mutations affect potassium channels," note the Mayo Clinic researchers. The genetic defect can be inherited in an autosomal dominant manner (Romano-Ward syndrome) or an autosomal recessive manner (Jervell and Lange-Nielsen syndromes).
Risk factors for the development of this disease
The main risk factors include:
- Gender of the patient (women are more at risk)
- Hormonal changes (especially during puberty and pregnancy)
- Taking certain medications (class IA and III antiarrhythmic drugs, antibiotics, antipsychotics)
- Electrolyte disturbances (hypokalemia, hypomagnesemia)
- Bradycardia and pause arrhythmias
Of particular danger are combinations of various risk factors that can significantly increase the severity of QT prolongation.
Diagnosis of this disease
The main symptoms include:
- Fainting states (syncope)
- Cramps
- Palpitations
- Sudden cardiac death
The following methods are used for diagnostics:
- ECG (the main diagnostic method)
- Holter monitoring
- Genetic testing
- Treadmill test
- Electrophysiological study
"Differential diagnosis must include other causes of syncope and seizures," emphasize the American Heart Association.
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