Syndrome of prolonged QT interval in adults and children

Most of us have had an electrocardiogram at least once in our life. For an ignorant person, her result is a tape of millimeter paper with several straight lines that periodically jump. Simplified, the distance between adjacent teeth in seconds is the length of the interval qt. Its duration is affected by the heart rate, sex, age, intake of certain medications, even the time of day. Normal values of qt lie in the range 320-430 ms for men and 320-450 ms for women. An interval is considered to be longer, when these figures are exceeded by 50 ms. The long interval syndrome qt (yQT) refers to ventricular arrhythmias.

Epidemiology

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

[1], [2], [3], [4], [5],

Causes of the syndrome of prolonged QT interval

Causes of the syndrome of the lengthened interval can consist in the following:

• poisoning with drugs, a list of drugs that extend the interval qt:
  • antiarrhythmic (aymalin, disopyramide, sotalol, quinidine);
  • psychotropic (aminazine, amitriptyline);
  • β-adrenomimetics (fenoterol, salbutamol);
  • arterial vasodilators (phentolamine, dihydropyridine);
  • antihistamine (terfenadine, astemizole);
  • antibiotics (biseptol, erythromycin);
  • diuretics (furosemide);
  • prokinetics (cisapride, metoclopramide)
• violation of electrolyte balance (lack of potassium, calcium, magnesium in the body);
• pathology and trauma from the central nervous system (swelling, hemorrhage, embolism);
• myocardial infarction, allergic or infectious disease;
• diseases of the cardiovascular system (hypertension, congenital heart disease, IHD);
• poisoning with phosphorus, mercury, arsenic;
• heredity.

[6], [7], [8], [9]

Risk factors

The risk factors for the long interval qt syndrome include pathological conditions such as diabetes mellitus, anorexia nervosa, obstructive pulmonary diseases, vegetovascular dystonia, hypothyroidism of the thyroid gland. In turn, lung diseases often occur against a background of long-term smoking, finding in polluted with harmful gases and vapors premises. Promotes the syndrome of the lengthened interval qt hypothermia, alcohol, low-calorie diet, protein deficiency.

[10], [11], [12], [13], [14], [15],

Pathogenesis

The main factor in the pathogenesis of the prolonged interval syndrome is qt, scientists call the imbalance of sympathetic effects on the heart, when the parasympathetic department of the ANS over the sympathetic prevails. More in detail, the pathogenesis of the syndrome is associated with impaired electrical activity of the ventricles - the time from electrical excitation (depolarization) to the restoration of the electric charge of the myocardium (repolarization). In the first case, activation of the heart occurs due to the opening of sodium channels and the penetration of sodium ions into the cells carrying a positive charge. Thus, the so-called membrane potential, reaches its peak. During repolarization, he returns to the original level. At this time, the path to the cell for sodium is closed, but the potassium ions can freely exit through the cell membrane outward, bringing its charge closer to the original one. An increase in the duration of this phase leads to the onset of the syndrome.

[16], [17], [18], [19]

Symptoms of the syndrome of prolonged QT interval

Symptoms of the syndrome of the prolonged interval qt are as follows:

• syncope from short-term (1-2min.) to deep (up to 20min.);
• convulsions similar to epileptic seizures;
• darkness in eyes, weakness;
• chest pain;
• tachycardia.

First signs

Channels through which the currents flow, due to the movement of sodium, potassium, magnesium, are in the cardiomyocyte - the cell of the heart muscle. Studies show that the functions of these channels are programmed at the genetic level. To date, there are 12 variants of the gene variants of the long interval syndrome qt. They have different symptoms, the course of the disease, treatment and prognosis. Most often there are three of them. The first signs of one of the options are fainting under stressful situations, physical activity, entering the water. In the second case, a loud sound can lead to a loss of consciousness. Another evidence of the disease is fainting in a calm state, during sleep, heart failure.

[20]

Extended interval qt in a child

The extended interval qt in a child is characteristic of the Timothy syndrome. Evidence of this pathology is autism, fused fingers and toes, a broad nose. If such a child still happens and fainting, then this is a signal to turn to the cardiologist. Another type of syndrome of the lengthened interval is Anderson syndrome. Its clinical sign is a chamfered chin, low-lying ears, hyperkinesia of the muscles, after which a syncope follows. The size of the interval for young children should not exceed 400 ms, the average interval - 460 ms, the older one - 480 ms. Exceeding these indicators indicates a disease.

[21], [22], [23], [24], [25], [26]

Forms

The syndrome of the elongated interval qt is divided into two types:

• congenital;
• acquired.

The congenital syndrome of etiology is divided into hereditary and occurred as a result of spontaneous gene mutations. The acquired extended interval qt can have an acute stage, provoked by such factors as poisoning with the above medicines, diseases of the cardiovascular system, traumas and brain tumors, thromboses, etc. The chronic stage arises from chronic pathologies not only of the cardiac system but also of other bodies. Also distinguish the syndrome of the extended interval qt in terms of the risk of fatal arrhythmias: low, medium and high.

[27], [28], [29], [30]

Complications and consequences

Consequences and complications of the syndrome of the elongated interval qt consist in the development of tachycardias, various arrhythmias of the heart, in which the 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 the onset of death.

[31], [32], [33], [34], [35]

Diagnostics of the syndrome of prolonged QT interval

The first steps in diagnosing the syndrome of the elongated interval qt are to find out the patient's anamnesis, conduct instrumental studies and calculate the corrected value of the interval qt using the special formula of Bazetta.

Diagnosis of congenital syndrome is carried out according to the following main diagnostic criteria: interval duration exceeding 0.44 s, syncope, presence of a syndrome in relatives. May also help additional: slow pulse (in children), congenital deafness, other physical disorders.

Laboratory blood test reveals a deficiency of magnesium and potassium. Blood is taken from the vein in the morning on an empty stomach. In the case of congenital syndrome of the elongated interval qt, genetic research is carried out to determine its genotype, which is very important for determining the treatment and the formation of a safe lifestyle.

The main method of instrumental pathology diagnostics is electrocardiography. In addition to the usual procedure, in the absence of eloquent symptoms of the syndrome, QQT resort to exercise ECG tests in order to provoke their appearance. Apply and diurnal or Holter ECG monitoring. The device is fixed on the body and within 24 hours records the performance of the heart.

[36], [37], [38], [39]

Differential diagnosis

Differentiated diagnosis of the syndrome of the prolonged interval qt is carried out with transient uQT on the background of drug treatment, with syncope of neurogenic nature, epilepsy, Brugada syndrome, ventricular arrhythmias, idiopathic forms of rhythm disturbance.

[40], [41], [42], [43], [44], [45]

Treatment of the syndrome of prolonged QT interval

Treatment of the syndrome of the elongated interval qt does not have a single tactic or protocol and is based on drug therapy with antiarrhythmic drugs, surgical interventions, implant implants - pacemakers. 

More details about treatment read in this article.

Prevention

When identifying the congenital syndrome of the prolonged interval qt, preventive measures consist in avoiding the impact of factors capable of causing an attack (emotional stress, physical stress, loud sounds, depending on the type of syndrome). At an average and high risk of fatal arrhythmias, preventive therapy is carried out - a constant intake of beta-blockers. Patients with low risk are continuously monitored. The most reliable preventive measure is the installation of a cardioverter-defibrillator in combination with beta-blockers.

[46], [47], [48], [49],

Forecast

The acquired syndrome of the extended interval qt is reversible after eliminating the factors that caused the disturbances. The prognosis for children with Timothy syndrome, not detected at an early stage of life, is unfavorable - such children do not live up to 30 years. Quite often lethal outcome - sudden death occurs with people having a pathology at the gene level. Unfortunately, this problem remains unresolved at this stage.

[50], [51], [52], [53], [54]