Prolonged QT syndrome in adults and children

Most of us have had to do an electrocardiogram at least once in our lives. For the uninitiated, its result is a strip of millimeter paper with several straight lines that periodically jump. Simply put, the distance between adjacent teeth in seconds is the length of the qt interval. Its duration is affected by heart rate, gender, age, intake of certain medications, even the time of day. Normal qt values are in the range of 320-430 ms for men and 320-450 ms for women. An interval is considered extended when these figures are exceeded by 50 ms. Long qt syndrome (yQT) refers to ventricular heart rhythm disturbances.

Epidemiology

According to statistics, one person per 3-5 thousand people suffers from the genetic syndrome of the long QT interval. This is approximately 85% of all patients, and more than half of the cases (60-70%) are female. Scientists do not exclude that cases of acquired disease are also associated with carriers of genotypes that are predisposed to the development of the syndrome under the influence of certain circumstances.

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Causes prolonged QT syndrome

Causes of long interval syndrome may include the following:

• drug poisoning, list of drugs that prolong the qt interval:
  • antiarrhythmics (ajmaline, disopyramide, sotalol, quinidine);
  • psychotropic (chlorpromazine, amitriptyline);
  • β-adrenergic agonists (fenoterol, salbutamol);
  • arterial vasodilators (phentolamine, dihydropyridine);
  • antihistamines (terfenadine, astemizole);
  • antibiotics (biseptol, erythromycin);
  • diuretics (furosemide);
  • prokinetics (cisapride, metoclopramide)
• electrolyte imbalance (lack of potassium, calcium, magnesium in the body);
• pathologies and injuries of the central nervous system (tumor, hemorrhage, embolism);
• myocardial infarction, allergic or infectious damage;
• cardiovascular diseases (hypertension, congenital heart defects, coronary heart disease);
• poisoning with phosphorus, mercury, arsenic;
• heredity.

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Risk factors

Risk factors for the development of long QT syndrome include such pathological conditions as diabetes mellitus, nervous anorexia, obstructive pulmonary diseases, vegetative-vascular dystonia, and hypothyroidism. In turn, lung diseases often occur due to long-term smoking, being in rooms polluted with harmful gases and vapors. Long QT syndrome is promoted by hypothermia, alcohol, low-calorie diet, and protein deficiency.

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Pathogenesis

Scientists believe that the main factor in the pathogenesis of the long QT syndrome is an imbalance of sympathetic influences on the heart, when the parasympathetic division of the ANS prevails over the sympathetic one. In more detail, the pathogenesis of the syndrome is associated with disturbances in the electrical activity of the ventricles - the time from electrical excitation (depolarization) to the restoration of the electrical charge of the myocardium (repolarization). In the first case, the heart is activated by opening sodium channels and the penetration of sodium ions into the cell, which carry a positive charge. In this case, the so-called membrane potential reaches its peak. During repolarization, it returns to its original level. At this time, the path into the cell for sodium is closed, but potassium ions can freely exit through the cell membrane, bringing its charge closer to the original one. An increase in the duration of this phase leads to the development of the syndrome.

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Symptoms prolonged QT syndrome

Symptoms of long QT syndrome include:

• fainting from short-term (1-2 min.) to deep (up to 20 min.);
• convulsions similar to epileptic seizures;
• darkening of the vision, weakness;
• chest pain;
• tachycardia.

First signs

The channels through which currents caused by the movement of sodium, potassium, and magnesium pass are located in the cardiomyocyte, a cell of the heart muscle. Research shows that the functions of these channels are programmed at the genetic level. To date, 12 variants of gene varieties of long QT syndrome are known. They have different symptoms, course of the disease, treatment, and prognosis. Three of them are most common. The first signs of one of the variants are fainting in stressful situations, physical exertion, or entering water. In the second case, a loud sound can cause loss of consciousness. Another sign of the disease is fainting in a calm state, during sleep, and cardiac arrest.

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Prolonged QT interval in a child

An extended QT interval in a child is typical for Timothy syndrome. Evidence of this pathology is autism, fused fingers and toes, a wide nose. If such a child also faints, then this is a signal to contact a cardiologist. Another type of extended interval syndrome is Anderson syndrome. Its clinical sign is a sloping chin, low-set ears, muscle hyperkinesis, followed by fainting. The interval in younger children should not exceed 400 ms, middle-aged - 460 ms, older - 480 ms. Exceeding these indicators indicates a disease.

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Forms

Long QT syndrome is divided into two types:

• congenital;
• acquired.

Congenital syndrome by etiology is divided into hereditary and resulting from spontaneous gene mutations. Acquired prolonged Qt interval can have an acute stage, provoked by such factors as poisoning with the above-mentioned drugs, cardiovascular diseases, brain injuries and tumors, thrombosis, etc. The chronic stage occurs due to chronic pathologies of not only the cardiac system, but also other organs. Also, the syndrome of prolonged Qt interval is distinguished by the degree of risk of fatal arrhythmia: low, medium and high.

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Complications and consequences

The consequences and complications of long QT syndrome include the development of tachycardia, various cardiac arrhythmias, in which individual muscles of the organ contract chaotically and uncoordinated. This leads to the inability of the heart to perform its functions and is often fraught with death.

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Diagnostics prolonged QT syndrome

The first steps in diagnosing long QT syndrome are to obtain the patient's medical history, conduct instrumental studies, and calculate the corrected QT interval value using the special Bazett formula.

Diagnosis of congenital syndrome is carried out according to the following main diagnostic criteria: interval duration exceeding 0.44 sec, fainting, presence of the syndrome in relatives. Additional criteria may also help: slow pulse (in children), congenital deafness, other physical disorders.

Laboratory tests of blood analysis reveal magnesium and potassium deficiency. Blood is taken from a vein in the morning on an empty stomach. In case of congenital long qt syndrome, genetic testing is carried out to determine its genotype, which is very important for determining treatment and forming a safe lifestyle.

The main method of instrumental diagnostics of pathology is electrocardiography. In addition to the usual procedure, in the absence of eloquent symptoms of the QT syndrome, they resort to stress ECG tests in order to provoke their appearance. Daily or Holter ECG monitoring is also used. The device is fixed on the body and records heart performance indicators for 24 hours.

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Differential diagnosis

Differential diagnostics of long QT syndrome is carried out with transient QT syndrome against the background of drug treatment, with fainting states of a neurogenic nature, epilepsy, Brugada syndrome, ventricular arrhythmias, and idiopathic forms of rhythm disturbance.

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Treatment prolonged QT syndrome

Treatment of long QT syndrome does not have a single tactic or protocol and is based on drug therapy using antiarrhythmic drugs, surgical interventions, and the introduction of implants - pacemakers.

For more information about treatment, read this article.

Prevention

When congenital long QT syndrome is detected, preventive measures include avoiding exposure to factors that can trigger an attack (emotional stress, physical exertion, loud sounds, depending on the type of syndrome). In cases of moderate to high risk of fatal arrhythmia, preventive therapy is administered - constant intake of beta-blockers. Patients with low risk are constantly monitored. The most reliable preventive measure is the installation of a cardioverter-defibrillator in combination with beta-blockers.

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Forecast

Acquired long QT syndrome is reversible after eliminating the factors that caused the disorders. The prognosis for children with Timothy syndrome, not detected at an early stage of life, is unfavorable - such children do not live to be 30 years old. A fairly common fatal outcome - sudden death occurs with people with pathology at the gene level. Unfortunately, this problem remains unsolved at this stage.

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