Long QT syndrome is a hereditary or acquired cardiovascular disease characterized by impaired ventricular repolarization. The pathology manifests itself as an extension of the QT interval on the electrocardiogram (ECG), which creates the preconditions for the development of potentially life-threatening arrhythmias, such as polymorphic ventricular tachycardia of the "pirouette" type and sudden cardiac death. According to the study by Schwartz et al. (2009), cases where the QT interval exceeds 500 ms are especially dangerous, increasing the risk of developing malignant arrhythmias by 10 times compared to normal values.
History of the disease and interesting historical facts
The first description of long QT syndrome was made in 1957 by Danish cardiologists Antoon Jervell and Fred Lange-Nielsen, who discovered a link between deafness and a tendency to sudden death in children. It is interesting to note that in 1963, American physician Bernard Lown introduced the term "tachyarrhythmic shock", describing the mechanisms of development of fatal arrhythmias in this syndrome. An important step in the study of the pathology was the discovery in 1995 of the first genes responsible for the development of the syndrome - KCNQ1 and HERG. According to the historical analysis conducted by Gussak et al. (2000), more than 40% of the first clinical observations were associated with cases of sudden death of young athletes.
Epidemiology (statistics of disease occurrence)
According to modern epidemiological studies, the prevalence of congenital long QT syndrome is approximately 1:2000 newborns. However, it is worth noting a significant proportion of undiagnosed cases, especially among patients with a latent form of the disease. Statistics indicate that about 0.4% of the population have borderline QT interval values, which requires constant monitoring. In the age group of 15-40 years, the incidence of sudden cardiac death associated with this pathology is about 1.3 cases per 100,000 people/year.
Genetic predisposition to the disease (involved genes and mutations)
To date, more than 17 genes have been identified, mutations in which can lead to the development of long QT syndrome. The main genes and their characteristics are presented in the table:
- KCNQ1 — encodes the α-subunit of the potassium channel IKs, mutations are detected in 30-35% cases
- KCNH2(HERG) — is responsible for the formation of the fast component of the slow rectifying potassium conductivity IKr, occurs in 25-30% cases
- SCN5A - encodes the α-subunit of the INa sodium channel, found in 5-10% cases
- CACNA1C - participates in the regulation of calcium channels, associated with a severe variant of the disease (Timothy syndrome)
It is important to note that most mutations are transmitted in an autosomal dominant manner, although recessive forms of the disease also exist.
Risk factors for the development of this disease (physical and chemical risk factors, other possible ones associated with this disease)
The development of the syndrome can be triggered by various environmental factors. The main triggers include:
- Electrolyte disturbances, especially hypokalemia and hypomagnesemia
- Taking certain medications, including class IA and III antiarrhythmic drugs
- Extreme physical activity, especially in individuals with a genetic predisposition
- Stressful situations and emotional tension
- Certain infectious diseases and febrile conditions
Diagnosis of this disease (Main symptoms, Laboratory tests, Radiological examinations, Other types of diagnosis of the disease, Differential diagnosis)
The key diagnostic method is a standard ECG with calculation of the corrected QTc interval. The following approaches are used to verify the diagnosis:
- Holter ECG monitoring for 24-48 hours
- Genetic testing to detect mutations
- Echocardiography to rule out structural heart disease
- Treadmill test for assessing QT dynamics during exercise
- Laboratory tests for blood electrolytes
In the differential diagnosis, it is necessary to exclude other causes of QT prolongation, such as hypertrophic cardiomyopathy and metabolic disorders.
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