What does the lengthening of the qt interval indicate? Prolonged qt interval in a child

NEUROLOGIST'S HANDBOOK

Relevance. Lack of awareness among pediatricians, therapists and neurologists about this disease often leads to tragic outcomes - sudden death of patients with Long-QT syndrome (LQTS). Also, in such patients, epilepsy is often overdiagnosed due to the clinical similarity of syncope (complicated by “convulsive syndrome”), which is incorrectly interpreted as classic epileptic seizures.

Definition. LQTS is a prolongation of the QT interval on the ECG (more than 440 ms), against the background of which paroxysms of ventricular tachycardia of the “pirouette” type occur. The main danger lies in the frequent transformation of this tachycardia into ventricular fibrillation, which often leads to loss of consciousness (fainting), asystole and death of the patient (sudden cardiac death [SCD]). Currently, LQTS is classified as frequent violations rhythm.

reference Information. The QT interval is the time period of the electrocardiogram (ECG) from the beginning of the Q wave to the return of the descending knee of the T wave to the isoline, reflecting the processes of depolarization and repolarization of the ventricular myocardium. The QT interval is a generally accepted and, at the same time, widely discussed indicator that reflects the electrical systole of the ventricles of the heart. It includes the QRS complex (fast depolarization and initial repolarization of the myocardium of the interventricular septum, the walls of the left and right ventricles), the ST segment (repolarization plateau), and the T wave (final repolarization).

Most important factor, which determines the duration of the QT interval, is the heart rate (heart rate). The dependence is nonlinear and inversely proportional. The duration of the QT interval is variable both within individuals and across populations. Normally, the QT interval is no less than 0.36 seconds and no more than 0.44 seconds. Factors that change its duration are: [ 1 ] Heart rate; [ 2 ] autonomous state nervous system; [3 ] the effect of so-called sympathomimetics (adrenaline); [ 4 ] electrolyte balance (especially Ca2+); [ 5 ] some medications; [ 6 ] age; [ 7 ] floor; [ 8 ] Times of Day.

Remember! The basis for determining QT interval prolongation is the correct measurement and interpretation of the QT interval relative to heart rate values. The duration of the QT interval normally varies depending on heart rate. To calculate (correct) the QT interval taking into account heart rate (= QTс) use various formulas (Bazett, Fridericia, Hodges, Framingham formula), tables and nomograms.

The lengthening of the QT interval reflects an increase in the time of excitation through the ventricles, but such a delay in the impulse leads to the emergence of prerequisites for the formation of a re-entry mechanism (the mechanism of re-entry of the excitation wave), that is, for repeated circulation of the impulse in the same pathological focus. Such a focus of impulse circulation (hyper-impulse) can provoke a paroxysm of ventricular tachycardia (VT).

Pathogenesis. There are several main hypotheses for the pathogenesis of LQTS. One of them is the hypothesis of a sympathetic imbalance of innervation (decreased right-sided sympathetic innervation due to weakness or underdevelopment of the right stellate ganglion and the predominance of left-sided sympathetic influences). The hypothesis of ion channel pathology is of interest. It is known that the processes of depolarization and repolarization in cardiomyocytes arise as a result of the movement of electrolytes into the cell from the extracellular space and back, controlled by the K+, Na+ and Ca2+ channels of the sarcolemma, the energy supply of which is provided by Mg2+-dependent ATPase. It is assumed that all LQTS variants are based on dysfunction various proteins ion channels. Moreover, the causes of disruption of these processes leading to prolongation of the QT interval may be congenital or acquired (see below).

Etiology. It is customary to distinguish between congenital and acquired variants of LQTS syndrome. The congenital variant is a genetically determined disease, occurring in one case per 3 - 5 thousand of the population, and from 60 to 70% of all patients are women. According to the International Registry, in approximately 85% of cases the disease is hereditary, while about 15% of cases are a consequence of new spontaneous mutations. To date, more than ten genotypes have been identified that determine the presence different options LQTS syndrome (all of them are associated with mutations in genes encoding structural units of cardiomyocyte membrane channels) and designated as LQT, but the most common and clinically significant are three of them: LQT1, LQT2 and LQT3.

Secondary etiological factors LQTS may include medications (see below), electrolyte disturbances (hypokalemia, hypomagnesemia, hypocalcemia); disorders of the central nervous system(subarachnoid hemorrhages, trauma, tumor, thrombosis, embolism, infections); heart disease (slow heart rate [ sinus bradycardia], myocarditis, ischemia [especially Prinzmetal's angina], myocardial infarction, cardiopathy, prolapse mitral valve- MVP [the most common form of LQTS in young people is the combination of this syndrome with MVP; the frequency of detection of QT interval prolongation in persons with MVP and/or tricuspid valves reaches 33%]); and etc. various reasons(low-protein diet, consumption of fatty animal foods, chronic alcoholism, osteogenic sarcoma, lung carcinoma, Conn's syndrome, pheochromocytoma, diabetes mellitus, hypothermia, neck surgery, vagotomy, familial periodic paralysis, scorpion venom, psycho-emotional stress). Acquired lengthening QT interval It is 3 times more common in men and is typical for older people with diseases in which coronarogenic myocardial damage predominates.

Clinic. The most striking clinical manifestations of LQTS, which in most cases are the primary reason for seeking medical attention, include attacks of loss of consciousness, or syncope, which are caused by life-threatening polymorphic VT specific to LQTS, known as “torsades de pointes” (pirouette-type ventricular tachycardia), or ventricular fibrillation (VF). Using ECG research methods, most often during an attack a special form of VT is recorded with a chaotic change in the electrical axis of the ectopic complexes. This spindle-shaped ventricular tachycardia, progressing to VF and cardiac arrest, was first described in 1966 by F. Dessertene in a patient with LQTS during syncope, which gave it the name “torsades de pointes”. Often, paroxysms (VT) are short-term in nature, usually end spontaneously and may not even be felt (LQTS may not be accompanied by loss of consciousness). However, there is a tendency for arrhythmic episodes to recur in the near future, which can cause syncope and death.

read also the article “Diagnostics of ventricular arrhythmias” by A.V. Strutynsky, A.P. Baranov, A.G. Elderberry; Department of Propaedeutics of Internal Diseases, Faculty of Medicine, Russian State Medical University (magazine “General Medicine” No. 4, 2005) [read]

The literature shows a stable relationship between precipitating factors and syncopal episodes. When analyzing the factors that contribute to syncope, it was found that in almost 40% of patients, syncope is recorded against the background of strong emotional arousal (anger, fear). In approximately 50% of cases, attacks are provoked by physical activity (excluding swimming), in 20% - by swimming, in 15% of cases they occur during awakening from a night's sleep, in 5% of cases - as a reaction to sharp sound stimuli ( phone call, doorbell, etc.). If syncope is accompanied by tonic-clonic convulsions with involuntary urination, sometimes - defecation, differential diagnosis between syncope with a convulsive component and grand mal seizure is difficult due to the similarity of clinical manifestations. However, a careful study will reveal significant differences in the post-attack period in patients with LQTS - fast recovery consciousness and good degree orientation without amnestic disturbances and drowsiness after the end of the attack. LQTS is not characterized by personality changes typical of patients with epilepsy. The main distinguishing feature of LQTS should be considered the connection with established provoking factors, as well as presyncope in cases of this pathology.

Diagnostics. ECG is often of decisive importance in the diagnosis of major clinical options syndrome (the duration of the QT interval is determined based on an assessment of 3 - 5 cycles). An increase in the duration of the QT interval by more than 50 ms relative to normal values for a given heart rate (HR) should alert the investigator to exclude LQTS. In addition to the actual prolongation of the QT interval, the ECG allows us to identify other signs of electrical instability of the myocardium, such as T wave alternans (changes in the shape, amplitude, duration or polarity of the T wave, occurring with a certain regularity, usually in every second QRST complex), an increase in the dispersion of the interval QT (reflects the heterogeneity of the duration of the repolarization process in the ventricular myocardium), as well as accompanying rhythm and conduction disturbances. Holter monitoring (HM) allows you to set values for the maximum duration of the QT interval.

Remember! Measurement of the QT interval is of great clinical importance, mainly because its prolongation may be associated with an increased risk of death, including SCD due to the development of fatal ventricular arrhythmias, in particular polymorphic ventricular tachycardia [torsade de pointes]. , (TdP)]. Many factors contribute to prolongation of the QT interval, including special attention deserves the irrational use of medications that can increase it.

Drugs that can cause LQTS: [1 ] antiarrhythmic drugs: class IA: quinidine, procainamide, disopyramide, gilurythmal; IC class: encainide, flecainide, propafenone; Class III: amiodarone, sotalol, bretylium, dofetilide, sematilide; IV class: bepridil; others antiarrhythmic drugs: adenosine; [ 2 ] cardiovascular drugs: adrenaline, ephedrine, Cavinton; [ 3 ] antihistamines: astemizole, terfenadine, diphenhydramine, ebastine, hydroxyzine; [ 4 ] antibiotics and sulfonamides: erythromycin, clarithromycin, azithromycin, spiramycin, clindamycin, anthramycin, troleandomycin, pentamidine, sulfomethaxazole-trimethoprim; [ 5 ] antimalarial drugs: nalofantrine; [ 6 ] antifungal drugs: ketoconazole, fluconazole, itraconazole; [ 7 ] tricyclic and tetracyclic antidepressants: amitriptyline, nortriptyline, imipramine, desipramine, doxepin, maprotiline, phenothiazine, chlorpromazine, fluvoxamine; [ 8 ] neuroleptics: haloperidol, chloral hydrate, droperidol; [ 9 ] serotonin antagonists: ketanserin, zimeldine; [ 10 ] gastroenterological drugs: cisapride; [ 11 ] diuretics: indapamide and other drugs that cause hypokalemia; [ 12 ] other drugs: cocaine, probucol, papaverine, prenylamine, lidoflazin, terodiline, vasopressin, lithium preparations.

Read more about LQTS in the following sources:

lecture “Long QT syndrome” N.Yu. Kirkina, A.S. Volnyagina; Tula State University, medical school, Tula (magazine “Clinical Medicine and Pharmacology” No. 1, 2018 ; pp. 2 - 10) [read ];

article “Clinical significance of prolongation of QT and QTC intervals while taking medications” by N.V. Furman, S.S. Shmatova; Saratov Research Institute of Cardiology, Saratov (journal “Rational pharmacotherapy in cardiology” No. 3, 2013) [read];

article “Long QT syndrome - main clinical and pathophysiological aspects” N.A. Tsibulkin, Kazan State Medical Academy (magazine “Practical Medicine” No. 5, 2012) [read]

article “Long QT interval syndrome” Roza Khadyevna Arsentyeva, functional diagnostics doctor at the center for psychophysiological diagnostics of the Medical and Sanitary Unit of the Ministry of Internal Affairs of the Russian Federation for the Republic of Tatarstan (journal Bulletin of Modern Clinical Medicine No. 3, 2012) [read];

article "Syndrome extended interval QT" section - "Safety medicines"(magazine "Zemsky Doctor" No. 1, 2011) [read]

article “Acquired long QT interval syndrome” by E.V. Mironchik, V.M. Pyrochkin; Department of Hospital Therapy of the Educational Institution "Grodno State Medical University" (Journal of GrSMU No. 4, 2006) [read];

article “Long QT syndrome - clinical picture, diagnosis and treatment” by L.A. Bockeria, A.Sh. Revishvili, I.V. Pronicheva Science Center cardiovascular surgery them. A.N. Bakulev RAMS, Moscow (journal “Annals of Arrhythmology” No. 4, 2005) [read]

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The QT interval doesn't tell you much to an ordinary person, but it can tell the doctor a lot about the condition of the patient’s heart. Compliance with the norm of the specified interval is determined based on the analysis of the electrocardiogram (ECG).

An electrocardiogram is a recording of the electrical activity of the heart. This method of assessing the condition of the heart muscle has been known for a long time and is widespread due to its safety, accessibility, and information content.

The electrocardiograph records the cardiogram on special paper, divided into cells 1 mm wide and 1 mm high. At a paper speed of 25 mm/s, the side of each square corresponds to 0.04 seconds. A paper speed of 50 mm/s is also often found.

An electrical cardiogram consists of three basic elements:

teeth;
segments;
intervals.

QT interval on ECG: the norm is in the range of 0.35-0.44 seconds

A spike is a kind of peak that goes either up or down on a line graph. The ECG records six waves (P, Q, R, S, T, U). The first wave refers to the contraction of the atria, the last wave is not always present on the ECG, so it is called intermittent. The Q, R, S waves show how the heart ventricles contract. The T wave characterizes their relaxation.

A segment is a straight line segment between adjacent teeth. The intervals are a tooth with a segment.

To characterize the electrical activity of the heart highest value have PQ and QT intervals.

The first interval is the time it takes for excitation to travel through the atria and the atrioventricular node (the conduction system of the heart located in the interatrial septum) to the ventricular myocardium.

The QT interval reflects the combination of processes of electrical excitation of cells (depolarization) and return to a resting state (repolarization). Therefore, the QT interval is called electrical ventricular systole.

Why is the length of the QT interval so significant in ECG analysis? Deviation from the norm of this interval indicates a disruption in the processes of repolarization of the ventricles of the heart, which in turn can result in serious disturbances of the heart rhythm, for example, polymorphic ventricular tachycardia. This is the name for malignant ventricular arrhythmia, which can lead to sudden death of the patient.

Normal interval durationQTis within 0.35-0.44 seconds.

The length of the QT interval can vary depending on many factors. The main ones:

age;
heart rate;
state of the nervous system;
electrolyte balance in the body;
Times of Day;
the presence of certain medications in the blood.

If the duration of the electrical systole of the ventricles goes beyond 0.35-0.44 seconds, the doctor has reason to talk about the occurrence of pathological processes in the heart.

Long QT syndrome

There are two forms of the disease: congenital and acquired.

ECG for paroxysmal ventricular tachycardia

Congenital form of pathology

It is inherited in an autosomal dominant manner (one of the parents passes the defective gene to the child) and an autosomal recessive type (both parents have the defective gene). Defective genes disrupt the functioning of ion channels. Experts classify four types of this congenital pathology.

Romano-Ward syndrome. The most common occurrence is approximately one child in 2000 births. It is characterized by frequent attacks of torsades de pointes with an unpredictable rate of ventricular contraction.

The paroxysm may go away on its own, or it may develop into ventricular fibrillation with sudden death.

The attack is characterized by following symptoms:

pale skin;
rapid breathing;
convulsions;
loss of consciousness.

Physical activity is contraindicated for the patient. For example, children are exempt from physical education lessons.

Romano-Ward syndrome is treated with medication and surgery. At medicinal method the doctor prescribes the maximum acceptable dose of beta-blockers. Surgical intervention performed to correct the conduction system of the heart or install a cardioverter-defibrillator.

Jervell-Lange-Nielsen syndrome. Not as common as the previous syndrome. In this case we observe:

more noticeable prolongation of the QT interval;
increased frequency of attacks of ventricular tachycardia, which can lead to death;
congenital deafness.

Mainly used surgical methods treatment.

Andersen-Tawil syndrome. This is a rare form of a genetic, inherited disease. The patient is susceptible to attacks of polymorphic ventricular tachycardia and bidirectional ventricular tachycardia. Pathology clearly makes itself known appearance patients:

short stature;
rachiocampsis;
low position of the ears;
abnormally large distance between the eyes;
underdevelopment of the upper jaw;
deviations in the development of fingers.

The disease can occur with varying degrees of severity. The most effective method of therapy is the installation of a cardioverter-defibrillator.

Timothy syndrome. It is extremely rare. With this disease, maximum prolongation of the QT interval is observed. Every six out of ten patients with Timothy syndrome have various congenital heart defects (tetralogy of Fallot, patent ductus arteriosus, ventricular septal defects). A variety of physical and mental abnormalities are present. The average life expectancy is two and a half years.

The clinical picture is similar in manifestations to that observed with the congenital form. In particular, attacks of ventricular tachycardia and fainting are characteristic.

Acquired long QT interval on an ECG can be recorded for various reasons.

Taking antiarrhythmic drugs: quinidine, sotalol, ajmaline and others.
Violation electrolyte balance in organism.
Alcohol abuse often causes paroxysm of ventricular tachycardia.
Row cardiovascular diseases causes prolongation of the electrical systole of the ventricles.

Treatment of the acquired form primarily comes down to eliminating the causes that caused it.

Short QT syndrome

It can also be either congenital or acquired.

Congenital form of pathology

It is caused by a rather rare genetic disease that is transmitted in an autosomal dominant manner. Shortening of the QT interval is caused by mutations in the genes of potassium channels, which ensure the flow of potassium ions through cell membranes.

Symptoms of the disease:

attacks of atrial fibrillation;
attacks of ventricular tachycardia.

Study of families of patients with short interval syndromeQTshows what happened in them sudden deaths relatives when young and even infancy due to atrial and ventricular fibrillation.

The most effective treatment for congenital short QT syndrome is the installation of a cardioverter-defibrillator.

Acquired form of pathology

The cardiograph may reflect on the ECG a shortening of the QT interval during treatment with cardiac glycosides in case of overdose.
Short QT syndrome can be caused by hypercalcemia ( increased content calcium in the blood), hyperkalemia (increased potassium content in the blood), acidosis (a shift in the acid-base balance towards acidity) and some other diseases.

Therapy in both cases comes down to eliminating the causes of the short QT interval.

How to decipher an ECG analysis, norms and deviations, pathologies and diagnostic principles

), characterized by prolongation of the QT interval on the electrocardiogram (ECG), attacks of loss of consciousness against the background of episodes of life-threatening ventricular arrhythmias (most often ventricular tachycardia of the “pirouette” type) and high mortality, which in the absence of treatment reaches 40 - 70% during the first year after clinical manifestation. In some cases, SCD may serve as the first manifestation of SUIQT. The frequency of the syndrome, according to various sources, ranges from 1:2000 to 1:3000.

The QT interval reflects the electrical systole of the ventricles (time in seconds from the beginning of the QRS complex to the end of the T wave). Its duration depends on gender (in women the QT is longer), age (with age the QT lengthens) and heart rate (HR) (inversely proportional). For objective assessment QT interval currently uses the corrected (heart rate-adjusted) QT interval (QTc), determined using the Bazett formulas (see below).

Clinically, two main variants of SUIQT are identified: the most common in the population, Romano-Ward syndrome with an autosomal dominant type of inheritance and Jervell-Lange-Nielsen syndrome with an autosomal recessive type of inheritance. Since the first study proved genetic nature syndrome in 1997, more than 400 mutations were identified in 12 genes, responsible for the development of the syndrome, manifested by dysfunction of cardiac ion channels. Moreover, to date, in most countries, mutations in known genes are detected only in 50 - 75% of probands, which dictates the need for further study of the genetic mechanisms of the disease.

It should be remembered that SUIQT can be not only congenital, but also acquired syndrome, being a typical side effect of antiarrhythmic drugs (drugs) of classes I and III. Also, this pathology can be observed when using other, non-cardiological drugs, incl. antibiotics (clarithromycin, erythromycin, ciprofloxacin, spiromycin, bactrim, etc.), opioid analgesics (methadone), antihistamines (loratadine, diphenhydramine, etc.), antifungal drugs (ketoconazole, miconazole, fluconazole, etc.), antipsychotics (haloperidol, chlorpromazine), etc. Acquired prolongation of the QT interval can occur with atherosclerotic or post-infarction cardiosclerosis, with cardiomyopathy, against the background and after myo- or pericarditis; an increase in the dispersion (see below) of the QT interval (more than 47 ms) may also be a predictor of the development of arrhythmogenic syncope in patients with aortic heart defects.

Clinical manifestations of SUIQT are prolongation of the QT interval on the ECG, episodes of ventricular arrhythmia - most often ventricular fibrillation, less often ventricular polymorphic tachycardia, registered various methods, and syncope (which, as a rule, are associated with the development of ventricular fibrillation or flutter, less often - ventricular asystole). The disease is usually detected either against the background of pronounced QT prolongation with preventive examinations, or during a targeted examination in connection with attacks of loss of consciousness.

To date, the diagnosis of SUIQT remains a difficult task, especially in relation to controversial subclinical and silent forms of the disease, as well as in the syncopal form due to overdiagnosis in these cases of epilepsy.

A standard 12-lead ECG allows you to identify prolongation of the QT interval of varying severity, assess the dispersion of the QT interval and changes in the morphology of the T wave. Bazett's formula (QTс = QT / (RR)0.5 at RR< 1000 мс) остается наиболее популярным инструментом коррекции интервала QT по отношению к частоте сердечных сокращений (ЧСС). Согласно рекомендациям 2008 г., приняты следующие значения для определения удлинения интервала QT: для лиц женского пола QTc460 мс, для лиц мужского пола - 450 мс.

ECG signs of SUIQT:

the following interpretation

ECG leads

The diagnosis of ATS is rarely in doubt when QT prolongation is evident. However, about 30% of patients have threshold or subthreshold values of this interval (5 - 2 percentiles of the age distribution of the indicator), which, in the absence of syncope in patients, can be interpreted as doubtful.

Polymorphic ventricular tachycardia type " pirouette"(or ventricular flutter - TdP - torsade de pointes) is characterized by an unstable, constantly changing shape of the QRS complex and develops against the background of an extended QT interval. It is assumed that the mechanism of TdP may be triggered activity due to early afterdepolarizations, or a “reentry” mechanism due to pronounced transmural dispersion of repolarization. Ventricular tachycardia of the “pirouette” type in 45 - 65% of cases is preceded by a “short-long-short” sequence (“short-long-short” interval, including extrasystole).

The presence of SUIQT with a risk of transition to torsades de pointes should be suspected in all patients with sudden loss of consciousness, palpitations, convulsions, or cardiac arrest.

Optimizing the treatment of patients with SUIQT remains a difficult and not fully resolved problem. Recommendations for the treatment of SUIQT are based primarily on data from International Registers and specialized clinics; No prospective randomized studies have been conducted in this area. The main methods of treatment are beta-blocker therapy and left-sided sympathectomy (LSS), as well as implantation of a cardioverter-defibrillator. Development of gene-specific therapy is also underway.

Among the beta-blockers in the treatment of SUIQT, propranolol, nadolol and atenolol are most widely used; in addition, metoprolol and bisoprolol are prescribed in some clinics. Propranolol and nadolol are the most effective in the treatment of SUIQT. However, propranolol has a number of disadvantages associated with the need to take it four times, as well as the development of tolerance with long-term use. Nadolol does not have these disadvantages and is used twice a day at a dose of 1.0 mg/kg. Metoprolol is the least effective beta-blocker, the use of which is accompanied by a high risk of recurrence of syncope. For those patients who, despite taking the maximum allowable dose of beta-blockers, continue to have recurrent ventricular tachycardia, LSE is currently recommended.

Implantation of cardioverter defibrillators (ICDs) is one of the relatively new treatment methods for children with SUIQT. According to the recommendations of the American and European Societies of Cardiology from 2006, ICD therapy in combination with beta blockers, regardless of age, is indicated for: patients who have survived cardiac arrest (class I); those who have persistent syncope and/or ventricular tachycardia while taking beta blockers (class IIa); for the prevention of SCD in patients at high risk (SCD), for example, with a diagnosed second and third molecular genetic variant of the syndrome or with a QTc exceeding 500 ms (class IIb).

Studying molecular basis SUIQT has opened up opportunities for the use of gene-specific therapy. In all cases of the syndrome, there is an increase in the duration of the action potential, but the cellular mechanism underlying this is different. This is reflected not only in differences in clinical picture disease, but also affects the effectiveness of therapy. In 1995, P. Schwartz et al. convincingly demonstrated the effectiveness of the class I drug mexiletine in patients with LQT3. Another Class IC drug that has been used in the treatment of LQT3 is flecainide. In the group of patients with the SCN5AD1790G mutation, there was an increase in heart rate, a decrease in the duration of the QT interval, and suppression of T wave alternans during flecainide therapy.

All patients diagnosed with SUIQT, regardless of the volume of therapy, should be under continuous monitoring with assessment of the dynamics of all individual SCD risk markers at least once a year. Increased concentrations of risk factors and markers, which, for example, are typical for adolescent males with LQT1, serve as a basis for intensifying therapy. Monitoring can significantly reduce the risk of SCD even in patients with severe course syndrome.

The connection between an altered QT interval and SCD has been known for more than 50 years, but only recently has it become clear that not only prolongation of the QT interval, but also its shortening may be a predictor of SCD...

One of the common causes of severe ventricular arrhythmias is long QT syndrome. Both congenital and acquired forms are associated with disruption of the molecular mechanisms of electrical activity in the membrane of myocardial cells. The article discusses the main aspects of the pathogenesis, diagnosis, treatment and prevention of long QT interval syndrome, which are relevant in practical work therapist and cardiologist.

Long QT syndrome - the main clinical and pathophysiological aspects

One of the most frequent causes of serious ventricular arrhythmia syndrome is an elongated interval QT. Both congenital and acquired forms are related to its violation of the molecular mechanisms of electrical activity in the membrane of myocardial cells. The article discusses the main aspects of the pathogenesis, diagnosis, treatment and prevention of the elongated interval QT syndrome, current practice in the practitioner and cardiologist.

History of discovery and study. The first mention of the phenomenon of prolongation of the QT interval of the electrocardiogram and associated clinical manifestations dates back to 1957 and belongs to two Norwegian doctors A. Jervell and F. Lange-Nielsen, who published a description of a clinical case of the combination congenital deafness with recurrent attacks of loss of consciousness and prolongation of the QT interval on the ECG. This clinical and electrocardiographic picture was called by the authors surdo-cardiac syndrome, but later became known as Jervell-Lange-Nielsen syndrome (DLN). Similar cases have already been described in next year C. Woodworth and S. Levine. A few years after the first publication, in the early 60s, C. Romano and O. Ward independently described two families whose members exhibited recurrent episodes of loss of consciousness and prolongation of the QT interval, but had normal hearing. This pathology was much more common than DLN syndrome and was called Romano-Ward syndrome (RU). With the discovery of new genotypic and clinical variants, the combination of syncope of arrhythmic origin with an increased duration of the QT interval was named long QT syndrome (LQT). The results were subsequently published (Yanowitz F., 1966) experimental research on dogs that underwent unilateral stimulation of the stellate sympathetic node, which also led to a prolongation of the QT interval. The data obtained suggested that QT syndrome is associated with an imbalance of sympathetic influences on the heart. This point of view became the basis for clinical application left-sided sympathetic denervation of the heart in patients with various options QT syndrome. Although more subtle molecular mechanisms of this pathology were later identified, nevertheless, an imbalance of the sympathetic innervation of the heart can be considered as one of the factors in the pathogenesis of QT syndrome. This is evidenced by the positive clinical effect of left-sided sympathetic denervation of the heart in the majority of patients with this disease. A logical continuation of this concept was the widespread introduction into practice of preventive therapy with beta blockers, which currently remains one of the main directions of non-invasive treatment of such patients.

A significant help in the study of QT syndrome was the creation in 1979 of an international registry of patients with congenital prolongation of the QT interval. Today there are almost one and a half thousand families whose members have certain signs of QT syndrome. The total number of patients under observation in this way exceeds three and a half thousand. Studies based on information from this registry have served as the main source of data on the pathogenesis, genetic mechanisms, as well as risk factors and prognosis of the disease in question.

The clinical significance of conditions associated with prolongation of the QT interval has expanded significantly due to the discovery of the so-called acquired QT syndrome, which usually occurs as a result of taking certain medications. The acquired and transient nature of QT interval prolongation due to drug therapy does not make this variant of the syndrome less dangerous in terms of consequences and prognosis. Patients with this form of uQT syndrome are encountered in practice much more often than with its congenital forms, which determines its practical relevance.

Epidemiology and molecular mechanisms. Today, QT syndrome is considered as a group of conditions similar in pathogenesis, clinical picture, course and prognosis, united by the commonality of electrocardiographic manifestations in the form of varying degrees of prolongation of the QT interval in combination with a tendency to develop life-threatening cardiac arrhythmias. It is based on the asynchrony of repolarization of various parts of the ventricular myocardium and, as a consequence, an increase in its total duration. An electrocardiographic sign of asynchronous myocardial repolarization is prolongation of the QT interval, as well as the degree of its dispersion. A specific clinical manifestation of this condition is considered to be a tendency to syncope of arrhythmic origin and increased risk development of fatal cardiac arrhythmias, mainly ventricular tachycardia of the torsades de pointes type. It is customary to distinguish between congenital and acquired variants of the QT syndrome.

The congenital variant is a genetically determined disease, occurring in one case per 3-5 thousand of the population, with 60 to 70% of all patients being women. According to the International Registry, in approximately 85% of cases the disease is hereditary, while about 15% of cases are the result of new spontaneous mutations. In approximately 10% of patients with uQT syndrome, genotyping revealed at least two mutations associated with the genesis this state, which determines the variability of its clinical manifestations and the nature of inheritance. This suggests that the actual prevalence of genotypes predisposing to manifestations of QT syndrome is actually much wider than estimated based on the number clinical cases of this pathology. It is likely that patients with the acquired form of this syndrome are often latent carriers of such genotypes, which clinically manifest themselves under the influence of external provoking factors. This assumption makes the use of genotyping justified even in individuals with transient prolongation of the QT interval.

Clinical and genetic correlations have been most fully studied for Jervell-Lange-Nielsen and Romano-Ward syndromes. Autosomal recessive DLN syndrome, including congenital hearing impairment, occurs when the patient is homozygous for this characteristic, which determines the high degree of severity of clinical manifestations, and the QT duration often exceeds 0.60 s. RU syndrome is autosomal dominant and is associated with a heterozygous variant of carriage of these characteristics. At the same time, the arrhythmic component of the syndrome is expressed more moderately, and average duration QT is 0.50-0.55 s.

The pathogenesis of QT syndrome is associated with a disturbance in the electrical activity of the myocardium. Depolarization of the myocardium is determined by the opening of fast sodium channels and inversion of the charge of the cardiomyocyte membrane, and its repolarization and restoration of the original membrane charge occur due to the opening of potassium channels. On the ECG this process is represented by the QT interval. Impaired potassium or sodium channel function due to genetic mutations leads to slower myocardial repolarization and, consequently, to prolongation of the QT interval on the ECG. The amino acid sequences of most ion channels in myocardial cells have been studied quite well, as have the genome regions encoding their structure. Genetic typing of patients can not only shed light on the mechanism of arrhythmogenesis, but also significantly influence the choice of treatment tactics and its effectiveness. To date, thirteen genotypes have been identified that determine the presence of different variants of the QT syndrome and are designated as LQT, but the most common and clinically significant are three of them: LQT1, LQT2 and LQT3.

Main genotypesL.Q.T. Potassium transport during repolarization is mediated by several types of potassium channels. One of them is the most common mutation found in congenital syndrome yQT, defined as the LQT1 genotype. Due to the structural changes associated with this genotype, the function of the channels is suppressed, the release of potassium from the cell is slowed down, which leads to slower repolarization and prolongation of the QT interval on the ECG. Similar changes due to another mutation, they can occur with the second type of potassium channels, slightly different from the previous ones in kinetics and structure. A mutation in the gene encoding this type of channel is defined as the LQT2 genotype and leads to consequences largely similar to those of the LQT1 genotype. The third type of molecular defect identified in QT syndrome concerns sodium channels and leads to increased activity. Excessive sodium entry into myocardial cells also slows repolarization, leading to prolongation of the QT interval. This option disorders is designated as the LQT3 genotype.

Thus, despite certain differences in the molecular mechanisms, all three variants of the pathogenesis of this condition have a similar electrocardiographic picture in the form of prolongation of the QT interval. These genotypes of congenital yQT syndrome are the most common and occur in 95% of cases in which genotyping was performed. The degree of prolongation of the QT interval, the nature of changes in other elements of the cardiogram, as well as associated clinical and prognostic aspects can vary significantly among different genotypes. This will be determined by the homozygosity or heterozygosity of the individual for these characteristics, a combination of various mutations and polymorphisms, as well as external conditions, which may influence clinical manifestations available genotypes.

In approximately a quarter of all cases of congenital long QT interval, no evidence of changes in the amino acid structure of ion channels was detected. This indicates that, in addition to dysfunction of ion channels, there are other mechanisms that can influence the electrical activity of myocardial cells. In particular, there is an assumption about the inhomogeneity of the electrophysiological properties of different parts of the myocardium and the associated unequal sensitivity to factors that prolong repolarization, which leads to asynchrony of its course and the development of arrhythmias.

The variety of potential pathophysiological mechanisms complicates the ability to differentially diagnose individual variants of QT syndrome in everyday practice, especially when clinical symptoms could be provoked by medications. Uncertainty in understanding the genesis and predisposing factors of acquired QT syndrome requires the same careful attention to such patients as to individuals with proven congenital forms.

Diagnostic methods. In the field of vision of doctors, a patient with QT syndrome usually falls into following cases: either as a result of accidental detection of a prolonged QT interval on an ECG; or due to the development of an attack of loss of consciousness; or according to the results of Holter ECG monitoring, which revealed the presence of ventricular tachycardia of the torsade de pointes type or prolonged QT. Regardless of the nature of the symptoms at the onset of the disease, a maximum clinical and functional examination of the patient should be performed. The first stage of the diagnostic search is the calculation of the QT interval (QTc), corrected according to the Bazett formula (H. Bazett, 1920, modified by I. Taran, N. Szilaggi, 1947), equal to the ratio of the measured QT interval to the square root of the measured RR interval in seconds:

QTc = QT / √RR

The calculated QTc interval eliminates the differences in the actual duration of the QT interval at different heart rates, bringing it to a duration corresponding to a rhythm frequency of 60 per minute, and is a universal indicator of the duration of electrical ventricular systole. The following are most often used as threshold values for pathological prolongation of QTc in cardiological practice: QTc >0.43-0.45 s for men and QTc >0.45-0.47 s for women (European Agency for the Evaluation of Medical Products). The more the threshold is exceeded, the more reason we can talk about QT syndrome. A QTc duration >0.55 s indicates that this patient most likely has one of the forms of congenital QT syndrome, and there is a high probability of developing clinical symptoms of cardiac arrhythmia.

The next step is to evaluate the T wave morphology on the ECG. In accordance with the three mentioned genotypes of the QT syndrome, three types of changes in the configuration of the T wave are distinguished. The LQT1 genotype is characterized by the presence of a pronounced positive T wave with a wide base; for the LQT2 genotype, the presence of a small, often deformed or jagged T wave is considered typical; the LQT3 genotype is characterized by a prolongation of the ST segment and a pointed T wave (Fig. 1). The presence of changes in the T wave, typical for one or another variant of the QT syndrome, allows us to assume with greater confidence the congenital nature of this pathology. Practical significance determining the type of QT syndrome is that they have clinical features that should be taken into account when prescribing treatment and determining prognosis.

Figure 1. Diagram of T wave variants for different LQT genotypes

A necessary, although not always effective, study is Holter ECG monitoring. In addition to detecting episodes of torsade de pointes (TdP), this method may reveal characteristic changes in T wave morphology, prolongation of the QT and QTc interval, a tendency toward bradycardia, or a high degree of ventricular arrhythmic activity. The presence of episodes of tachycardia in combination with the above clinical and cardiographic signs confirms the diagnosis, but their absence in this recording does not exclude the possibility of their occurrence in other situations and, therefore, cannot serve as a basis for removing this diagnosis.

An additional diagnostic method for identifying asymptomatic cases of QT syndrome, according to some experts, may be stress ECG tests, which provoke the appearance diagnostic signs diseases. This test rarely gives positive results and is able to predominantly identify patients with the LQT1 genotype. At the same time, it is the carriers of this genotype who are exposed to most at risk during the test, because the main factor provoking ventricular arrhythmias in this group of patients is physical activity, and even the first arrhythmic episode can be fatal.

An alternative method to identify the tendency to prolong the QT interval in uncertain cases is the epinephrine or isopropylnorepinephrine test, which can also only be performed in an emergency preparedness setting for the occurrence of ventricular arrhythmias. Invasive electrophysiological testing to induce ventricular tachycardia rarely leads to a more accurate diagnosis and is unlikely to be recommended for use. Others diagnostic methods examinations of cardiac patients, as a rule, provide few additional opportunities for verification of QT syndrome. Laboratory research allow you to identify potassium or magnesium deficiency and determine function thyroid gland, however of decisive importance for diagnostics also do not have .

Genetic research in order to identify carriage of LQT genotypes, it seems desirable even in cases of undoubted and persistent QTc prolongation, suggesting the congenital nature of the diagnosed pathology, because genotypes differ significantly in the nature of the course, provoking factors, the effectiveness of drug therapy and prognosis. Thus, knowledge of the specific genotype of γQT syndrome allows us to create the safest lifestyle for the patient, as well as to individualize treatment tactics as much as possible. In addition, this will optimize the follow-up examination of the patient's family members, which should preferably be carried out before any of them develop clinical symptoms.

In the diagnosis of congenital QT syndrome, a key role is played by the patient's history regarding episodes of loss of consciousness and presyncope, interruptions in cardiac function, the arrhythmogenic effect of physical activity and medications recently taken. In addition, it is necessary to find out the presence of all of the above signs, as well as hearing impairment in the patient’s relatives. It is mandatory to analyze all available electrocardiograms in order to identify changes characteristic of this syndrome, and their dynamics.

At the end of the last century, a system of summary assessment of various diagnostic criteria syndrome yQT in points (P. Schwartz, 1993). This technique has not received widespread in domestic cardiology, but the previously proposed division of diagnostic signs into basic and additional ones seems relevant (Table 1). To make a diagnosis, two signs from each group are sufficient. Differential diagnosis carried out mainly with the following conditions: transient prolongation of the QT interval against the background drug therapy; ventricular arrhythmias occurring in other diseases; idiopathic forms of rhythm disturbances; syncope of neurogenic origin; Brugada syndrome; epilepsy.

Table 1.

Diagnostic criteria for congenital uQT syndrome (Schwartz, 1985)

* To make a diagnosis, two signs from each group are sufficient

Prognosis and clinical course. Based on the examination of the patient, it is possible to roughly estimate the risk of developing unfavorable clinical symptoms. High-risk factors in this regard are the following (Table 2): an episode of cardiac arrest with successful resuscitation; attacks of tachycardia such as pirouette recorded during Holter monitoring; congenital hearing impairment; family history of uQT syndrome; episodes of loss of consciousness and presyncope; recurrent episodes of ventricular tachycardia or syncope during therapy; QTc duration from 0.46 to 0.50 s and more than 0.50 s; 2nd degree atrioventricular block; hypokalemia and hypomagnesemia.

Table 2.

Risk factors for the development of ventricular arrhythmias in congenital QT syndrome

The risk of developing syncope and cardiac arrest depends on a number of factors, in particular, LQT genotype, gender, QTc duration (Table 3).

Table 3.

Risk stratification for congenital uQT syndrome (according to Ellinor P., 2003)

QTc
QTc
LQT1
LQT2
LQT3

B - high risk (>50%); C - average risk (30-50%); N - low risk (<30%)

In the absence of preventive treatment, the high-risk group (>50%) includes all carriers of the LQT1 and LQT2 genotypes with a QTc >0.50 c, as well as men with the LQT3 genotype with a QTc >0.50 c; The average risk group (30-50%) includes women with the LQT3 genotype with a QTc >0.50 s and the LQT2 genotype with a QTc<0.50 с, а также все лица с LQT3 и QTc <0.50 с; к группе низкого риска (<30%) относятся все лица с генотипом LQT1 и QTc <0.50 с, а также все мужчины с генотипом LQT2 и QTc <0.50 с. (Ellinor P., 2003). При отсутствии данных о генотипе пациента можно считать, что средний риск развития жизнеугрожающих аритмических событий в течение пяти лет колеблется от 14% для пациентов, перенесших остановку сердца, до 0.5% для лиц без специфической симптоматики в анамнезе и с удлинением QTс <0.50 с. Однако в связи с тем, что клинические проявления заболевания и его прогноз в течение жизни могут меняться, существует необходимость регулярного контроля за состоянием пациентов и периодического пересмотра ранее установленных уровней риска.

The patient's age plays a certain role in the prognosis of the disease. Men have a significantly greater risk of arrhythmic complications at a young age. Between the ages of twenty and forty years, the risk for both sexes is approximately equal, and later the risk of arrhythmic complications progressively increases for women. It is assumed that increased levels of androgens have a protective effect, and estrogens, on the contrary, can enhance the pathogenic effect of genetic disorders, and changes in hormonal levels can become a provoking factor in the development of arrhythmic episodes. This factor must be taken into account when prescribing treatment and monitoring the condition of patients.

The clinical course of congenital QT syndrome is very variable and depends on both the genotype and external factors of the patient’s life. Different LQT genotypes may determine different course and prognosis in congenital LQT syndrome. In particular, the main provoking factor for the LQT1 genotype is physical activity, and more than two-thirds of cases of arrhythmic manifestations occur precisely under such circumstances. The most typical provoking type of exercise for this genotype is swimming. Within the DLN syndrome, the LQT1 genotype is one of the most serious in terms of clinical symptoms and prognosis. The LQT2 genotype is characterized by the fact that clinical signs associated with ventricular arrhythmias most often occur at rest or during sleep, can be provoked by sudden auditory stimuli such as alarm clock ringing, and are practically unrelated to physical activity. It is noted that in some carriers of this genotype, an arrhythmic episode can be triggered by emotional factors. The LQT3 genotype is also characterized by a low dependence of arrhythmic symptoms on exercise, and about two thirds of such episodes occur at rest. Thus, in the daily life of an ordinary person, the LQT2 and LQT3 genotypes may more often become causes of cardiac arrhythmias.

A typical clinical course is persistent prolongation of QTc in combination with more or less frequent syncope or presyncope due to episodes of ventricular tachycardia. It is also possible to have asymptomatic carriers of LQT genotypes with normal QT interval duration, but the risk of its prolongation and the occurrence of cardiac arrhythmias under the influence of external factors. The most unfavorable course is complicated by cardiac arrest, requiring resuscitation measures. More than a quarter of new syncope episodes in previously asymptomatic individuals can occur with cardiac arrest, which emphasizes the need for diagnostic search and preventive therapy even in the asymptomatic period of the disease. The total mortality rate for all types of QT syndrome is about 6% by average age, differing significantly between individual variants. Complications of QT syndrome include sustained ventricular tachycardia, ventricular fibrillation, residual neurological symptoms after successful resuscitation, and trauma during the development of syncope.

Treatment and prevention. Drugs, surgical techniques, and implantable devices can be used to prevent life-threatening arrhythmias in people with congenital QT syndrome. The treatment tactics offered today are not fully standardized and verified due to the difficulty of conducting a comparative analysis of various treatment options. In any case, when receiving one or another treatment option, the patient should maximally avoid exposure to provoking factors specific to this type of QT syndrome, in particular physical activity for the LQT1 genotype and emotional stress for the LQT2 genotype. Specific recommendations for prevention for the LQT3 genotype are difficult, because the majority of clinical episodes occur at rest or during sleep.

Prescription of preventive therapy is justified for people at high and average risk of developing fatal arrhythmias, while patients with low risk should be kept under regular observation, but on an individual basis they can also be prescribed continuous treatment. Although therapy for asymptomatic carriers of LQT genotypes is controversial, the safest approach would be to prescribe drug prophylaxis to all individuals in this group, because even the first arrhythmic episode can be life-threatening. Low-risk patients do not require hospitalization and can be assessed and monitored on an outpatient basis. In contrast, patients who have experienced cardiogenic syncope or cardiac arrest should be hospitalized as soon as possible for differential diagnosis and prevention of recurrence.

Beta blockers are the first choice drugs for preventive treatment. They should be prescribed to everyone, including asymptomatic patients, with QTc exceeding standard values. In the recent past, it was necessary to prescribe high doses of drugs close to the maximum, but it is now believed that moderate therapeutic doses can be effective. Drugs in this group are most suitable for carriers of the LQT1 genotype who have physical activity as a factor in provoking arrhythmias. But even in this group of patients, treatment success is not guaranteed, and fatal arrhythmic episodes can occur even during therapy. At the same time, the number of life-threatening arrhythmias in patients treated in this way was reduced by almost half, and in some groups even more, so that the overall result of the use of beta blockers is regarded as satisfactory.

A certain exception in this case are patients with the LQT3 genotype, in whom arrhythmic episodes more often occur at rest. A significant number of these patients not only will not respond to beta-blocker therapy, but may be at additional risk due to excessive reduction in heart rate. Taking into account the mechanism characteristic of this type of QT syndrome, a positive effect is expected from the administration of sodium channel blockers, in particular flecainide and mexiletine. However, these therapeutic solutions are not generally accepted and require further testing of efficacy and safety. You can count on a positive effect from the implantation of pacemakers (pacers), which prevent the rhythm frequency from falling below a certain level. At the same time, the use of ECS for the LQT1 genotype is not entirely advisable.

If symptoms persist in patients at intermediate or high risk during medical treatment, left-sided sympathetic denervation of the heart may be performed. This intervention halved the number of patients with clinical symptoms and tripled the risk of developing potentially dangerous arrhythmias. An addition to the main methods of treatment may be regular intake of magnesium and potassium supplements to prevent hypokalemia and hypomagnesemia, which are common causes of arrhythmic episodes in people with congenital QT syndrome.

The most effective means of preventing life-threatening arrhythmias in patients with QT syndrome is the installation of an implantable cardioverter defibrillator (ICD) in combination with beta-blocker therapy. This approach dramatically reduces the risk of fatal arrhythmias and is appropriate in high-risk patients who do not respond to beta-blocker monotherapy. In selected patients who demonstrate frequent ICD firing despite concomitant beta-blocker therapy, the above-mentioned left-sided sympathetic denervation of the heart may be beneficial, reducing the number of ICD firings by more than 90%. Severe asymptomatic QTc prolongation >0.50 s, LQT2 and LQT3 genotypes, and Jervell-Lange-Nielsen syndrome may immediately require ICD implantation as the only reliable prophylactic agent.

Prevention of clinical manifestations of uQT syndrome involves: identifying high-risk individuals and prescribing appropriate preventive treatment for them; refusal of the patient to use medications that prolong the QT interval; prevention of situations associated with the formation of potassium or magnesium deficiency, and prompt correction of these conditions if they arise; control of thyroid function; warning the patient about the need to constantly take beta blockers and avoid specific precipitating factors, if any are identified; training the patient's family members in cardiopulmonary resuscitation techniques; examination of the patient’s relatives and limiting their use of drugs that prolong the QT interval.

Acquired long QT syndrome. In clinical practice, the acquired variant of QT syndrome is more common, usually associated with taking certain medications, in particular, up to 10% of people taking antiarrhythmic drugs may demonstrate prolongation of the QT interval. The mechanism of its development is in many ways similar to congenital QT syndrome, but the function of potassium channels is impaired not due to changes in their structure, but as a result of exposure to chemicals. The degree of prolongation of the QT interval is usually proportional to the plasma concentration of the drug causing the changes. The clinical picture of acquired QT syndrome is characterized by reversibility and a more benign course. It is believed that in some cases this pathology occurs in individuals who are asymptomatic carriers of LQT genotypes, and the drug only enhances the existing electrophysiological disorder. Therefore, patients with transient QT prolongation should undergo a complete evaluation and their family history should be carefully reviewed. Active early identification of individuals who are latent carriers of hereditary forms of QT syndrome can have a significant positive impact on its course and prognosis.

The most well-known drugs that have this effect include: antiarrhythmic drugs, mainly class IA and III; antibacterial drugs from the groups of macrolides and fluoroquinolones; a number of antidepressants and sedatives; some antihistamines, diuretics and lipid-lowering drugs; chemotherapeutic agents, as well as a number of others. All drugs currently approved for clinical use are tested for their ability to prolong the QT interval, so the list of potentially dangerous drugs is constantly growing. At the same time, prolongation of the QT interval during treatment with drugs such as amiodarone and sotalol can be regarded as a manifestation of their pharmacological action. A QT prolongation of 10% from the initial level can be considered acceptable, which can be assessed as a calculated risk. However, exceeding the QTc duration by more than 25% of normal or more than 0.52 s may pose a potential risk of developing life-threatening arrhythmia.

Risk factors for the occurrence of acquired QT syndrome during the use of these drugs are also: hypokalemia, hypomagnesemia, hypothyroidism, severe organic heart disease, bradycardia, combined antiarrhythmic therapy, alcoholism, anorexia nervosa, acute cerebrovascular accidents, subarachnoid hemorrhages, organophosphorus compounds and some other factors.

Therapeutic measures for this form of QT syndrome are aimed at discontinuing the drug that caused the electrophysiological disturbances. This, as a rule, is sufficient, and then the clinical condition and electrocardiographic picture are monitored. In case of pronounced prolongation of QT, the patient should be under monitored supervision in the intensive care unit, and if polymorphic ventricular tachycardia is detected, intravenous administration of magnesium and potassium preparations should be started. Beta blockers aimed at stopping torsades de pointes can apparently be used in this form of QT syndrome, but they are not the first choice drugs. The use of class IA, IC and III antiarrhythmic drugs that prolong the QT interval is contraindicated. If there is no clinical effect from drug therapy, temporary cardiac pacing may be used. In threatening situations, readiness to carry out resuscitation measures in full is necessary. After stopping the arrhythmia, preventive therapy and observation should continue for at least 24 hours.

In the future, the patient should be advised to refrain from taking medications that affect the duration of the QT interval. Timely assessment of the duration of the corrected QT interval from the first days of prescribed drug therapy, as well as active identification of an individual and family history of syncope and an initially prolonged QT interval make it possible to avoid severe and prognostically unfavorable clinical conditions with a high probability.

ON THE. Tsibulkin

Kazan State Medical Academy

Nikolay Anatolyevich Tsibulkin - Candidate of Medical Sciences, Associate Professor of the Department of Cardiology and Angiology

Literature:
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3. Hedley P.L., Jorgensen P., Schlamowitz S. et al. The genetic basis of long QT and short QT syndromes: a mutation update. Human Mutation. 2009;30(11):1486-511.
4. Medeiros A., Kaku T., Tester D. J., et al. Sodium channel B4 subunit mutation causes congenital long QT syndrome. Heart Rhythm. 2006;3:S34.
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Human health is the main component of a normal and quality life. But we don’t always feel healthy. Problems can arise for various reasons, and their importance may also vary. For example, the common cold does not cause concern among people; it is quickly cured and does not cause much harm to overall health. But if problems arise with internal organs, this is already more life-threatening and worsens our well-being for a long time.

Recently, a lot of people have been complaining about heart problems, and most often these are common diseases that are easy to treat and diagnose. But there are cases when a patient has long QT syndrome. In medicine, this term refers to a pronounced or acquired condition of a person, accompanied by an increase in the duration of a given interval on a segment of the cardiogram. Moreover, only prolongations of more than 55 ms from normal values are attributed to this syndrome. Moreover, when the disease develops, the deviation indicators of this interval can be more than 440 ms.

Manifestations

In most cases, this disease is asymptomatic for the patient himself, and it is almost impossible to detect it on his own. Basically, in people with this diagnosis, the processes of repolarization and depolarization are disrupted, due to changes in symmetrical This can only be noticed in the process of research, based on data from various types of equipment. The main factor causing this condition is electrical instability of the heart muscle.

People with long QT syndrome may develop ventricular tachycardia if there is ineffective or no treatment. These complications are much more dangerous for the lives of patients and are detrimental to the general condition. In this regard, if you suspect the presence of this disease, you should immediately take care of your health, otherwise bad consequences may occur. In addition, the complications of this disease are quite serious. They can lead not only to impaired performance and deterioration of the patient’s general well-being, but also to death.

Kinds

This deviation has been studied in medicine for a long time, and over the years scientists have been able to learn more and more about it. This disease is divided into two types, namely acquired and congenital long QT syndrome. It is possible to determine which type a patient has only through research. With a congenital disorder, there is a problem with the failure of the genetic code. When acquired, the development of the disease can be influenced by various factors.

Forms

There are also certain types of disease progression:

Hidden form. It is characterized by normal interval values during examination, and the first attack of syncope causes sudden death.
Syncope occurs, but the QT interval is not prolonged during testing.
The prolongation of the interval is isolated and is not reflected in the anamnesis.
Syncope occurs with a prolongation of the QT index, exceeding the norm by 440 ms or more.

Causes

Many factors can influence the development of this disease. For example, it begins to develop due to hereditary diseases, including R-U syndrome. In this case, attacks of loss of consciousness are very common, which actually lead to the development of this disease. And also E-R-L syndrome, if the patient has congenital deafness. Scientists have not yet been able to figure out what causes this combination of symptoms and how exactly it provokes the development of the disease.

Also, gene mutations can cause the development of this disease. This is the most basic cause of congenital disease, but in some cases it does not appear immediately, but only in adulthood, after suffering stress. Typically, it is problems with protein synthesis in sodium and potassium channels that become factors that provoke long QT syndrome. The reason may lie in the side effects of taking certain medications. The greatest threat is posed by strong antibiotics, which the patient may take to treat other diseases.

The disease can be caused by metabolic disorders or diets aimed at reducing calories in food. Exhaustion of the body in such situations can affect not only the heart. Therefore, it is better to coordinate such diets with a doctor and constantly be under his supervision. Exhaustion can lead to complications of certain cardiovascular diseases, such as coronary disease or the syndrome sometimes develops due to pathologies of the central nervous system and with vegetative-vascular dystonia, as well as other disorders of the autonomic nervous system.

Symptoms

There are specific signs that indicate that the patient has long QT syndrome. The symptoms of this disease are as follows:

Loss of consciousness lasting from a couple of minutes to a quarter of an hour. In some cases, an attack can last up to twenty minutes.
Convulsions during synoptic conditions are similar to epileptic attacks in appearance, but the processes that provoke them are completely different.
Sudden weakness in the body, accompanied by darkening of the eyes.
Palpitations even in the absence of physical activity or emotional stress.
Chest pain of various types, continuing during an accelerated heartbeat, as well as accompanying fainting or dizziness and numbness of the arms and legs.

Diagnostics

Very often, long QT syndrome, in children especially, occurs without symptoms. In such a situation, the patient may feel completely healthy and suddenly die. Therefore, if a person is at risk of the disease, it is necessary to be regularly examined by a doctor to exclude the possibility of developing the disease. To diagnose the disease, modern medicine uses several methods.

If there is a suspicion that a patient has long QT syndrome and health problems clearly indicate this, then electrocardiography is the most important test to determine the disease. Carrying it out during an attack, the device will show signs of ventricular tachycardia, turning into ventricular fibrillation. This method is the main one in determining the form of the disease.

There is also another test that can look for long QT syndrome. It is carried out throughout the day. Therefore, it is called 24-hour monitoring and allows you to record the patient’s cardiac activity during this period. A small device is attached to his body, which records the readings of the heart, and after it is removed, the specialist deciphers the data recorded by the device. They make it possible to determine whether the patient has severe rigid bradycardia, whether the morphology of the T wave is changing, and whether there are disturbances in the processes of myocardial repolarization and ventricular extrasystole.

Treatment

If a patient has been diagnosed with long QT interval syndrome, treatment must be comprehensive and adequate, because this is the only way to prevent the development of complications that are dangerous to health and can be fatal.

Drug therapy

The disease can be cured using antiarrhythmic drugs. A properly selected course of medication will not only eliminate the symptoms of this disease, but will also stabilize the functioning of the cardiovascular system for a long period. This is one of the methods to cure congenital long QT syndrome LQTS.

Surgery

If a patient is at risk of life-threatening illness due to arrhythmia in this disease, experts recommend implantation of a pacemaker. Its job is to normalize the contraction frequency of the heart muscle. Modern medicine has developed special devices that detect pathological abnormalities in the functioning of the heart. The disease can be caused externally. During physical activity, for example, the device will not respond. But if the impulses are pathological in nature, it normalizes the functioning of the organ.

Surgery for a disease such as long QT syndrome is simple and quite safe. The pacemaker is attached to the left of the pectoralis major muscle. Electrodes come from it, which surgeons attach to the required area, passing them through the subclavian vein. The device can be configured using a programmer. With its help, you can change the parameters of cardiac stimulation, depending on the personal characteristics of the patient. The device will turn on every time the work of the heart muscle goes beyond the specified parameters.

Conclusion

This disease cannot always be diagnosed, since it rarely manifests itself clearly. But at the same time, the threat to the patient’s health is very great. Therefore, if there is even a slight risk of its occurrence, it is worth constantly undergoing examinations and consulting with specialists.