Congenital long QT syndromes (LQTS) is a group of serious heart diseases involving disturbances in the flow of ions through the cell membranes of cardiomyocytes. Despite the normal structure of the heart and its mechanical function, it can lead to arrhythmias and sudden cardiac arrest. Find out who is at risk of developing LQTS, what their symptoms are, and how to prevent arrhythmia.

Contents:

  1. QT interval - what is it?
  2. Meaning of the corrected QT interval
  3. Congenital long QT syndrome
  4. Long QT syndrome - symptoms and diagnosis
  5. Long QT syndrome - treatment

Congenital long QT syndrome is very rare. It is caused by a genetic disease and most often appears together with other defects, e.g. deafness.

This disease results from damage to ion channels, which are membrane proteins, which in turn disrupts the flow of ions in the cells of the heart muscle. The risk of this disturbance of the electrical activity of the heart muscle is related to the risk of dangerous arrhythmias and cardiac arrest.

The first symptom most often is syncope due to arrhythmia, therefore it is necessary to look for QT interval prolongation in relatives who have experienced sudden cardiac death or were diagnosed with LQTS.

The treatment involves prophylactic pharmacotherapy, and if it is insufficient, a cardioverter-defibrillator is implanted. After the diagnosis of a prolonged QT interval, it is necessary to remain under the constant observation of a cardiologist, among others, in order to evaluate the indications for the implantation of a cardioverter-defibrillator.

QT interval - what is it?

The EKG curve is a recording of the electrical activity of the heart muscle. The horizontal line represents the resting potential, i.e. the lack of electrical activity. A stimulus acting on a cell changes the properties of its membrane, it becomes permeable to ions and the electric charge of the cell changes - depolarization occurs. The process of this charge returning to normal is due to re-ion shifts and is called repolarization. It is these changes in the electric charge of the cells (depolarization or repolarization) that are reflected as the ECG curve shifts during the performance of this test.

The QT interval is the portion of the ECG curve between the beginning of the Q wave and the end of the T wave, it is a record of the entire electrical activity of the heart chambers. It includes the entire QRS complex, which reflects the depolarization of the ventricles, as well as the ST segment and the T wave, which in turn speak of repolarization, i.e. the return of the ventricular muscle to its resting potential. The length of the QT interval depends on the heart rate, the efficiency of the ionic carriers and, to a small extent, also on gender and age.

Abnormalities in the QT interval can contribute to the development of serious arrhythmias. This is because abnormal QT prolongation indicates irregular repolarization and therefore different duration of myocardial electrical hypersensitivity.

The aforementioned hypersensitivity is a physiological, normal phenomenon, it is characterized by an excessively intense electrical response to the active stimulus and occurs after each stimulation of cardiomyocytes. This increased cardiac response contributes to the development of ventricular arrhythmias.

In patients with illnesses, the prolongation of the period of repolarization and hypersensitivity makes it possible that the next electrical stimulation of the heart muscle will occur during this hypersensitivity, which will cause arrhythmia.

This can be ventricular tachycardia, ventricular fibrillation, or torsade do pointes, which may resolve on its own or develop into ventricular fibrillation. All of these arrhythmias are life threatening and lead to death unless emergency action is taken immediately.

These arrhythmias are rare, but because of their dangers, it is imperative to seek and treat people with a long QT interval.

It is worth mentioning that in he althy people the refractory period is constant and it is not possible to "superimpose" another stimulation on the previous ones.

Extending the QT interval may result from:

  • taking certain medications, especially several medications that may have such an effect, e.g. psychotropic drugs, antiallergic drugs, antibacterial drugs, or some that affect the work of the heart
  • electrolyte disorders - calcium deficiency, potassium or magnesium deficiency
  • myocardial ischemia
  • birth defects related to ion transporters - most often potassium, less often sodium
  • diseases of the central nervous system causing an increase in intracranial pressure
  • pheochromocytoma
  • poison
  • Brugada team

Meaning of the corrected QT interval

The diagnosis of a long QT interval is based on the calculation of the corrected QT interval, this isnecessary because, as mentioned, its length depends on the heart rate. In practice, the Bazett formula is used, in which the measured QT interval is divided by the root of the R-wave distance. A prolonged QT interval occurs when the conversion is greater than 460 milliseconds for women or 450 ms for men.

Congenital long QT syndrome

This is a group of 15 hereditary diseases in which ion channels are damaged as a result of many different mutations (over 500 have been described). This causes heterogeneity in repolarization, prolongation of the QT interval, predisposing to torsade de pointes and sudden cardiac death.

The most common diseases are:

  • Jervell-Lang-Nielsen syndrome - inherited autosomal recessively. It occurs in over 40% of patients with congenital prolongation of the QT syndrome. In addition, it is associated with deafness and a lack of speech development. Physical exertion or a strong emotional stimulus predispose to the occurrence of a rhythm disturbance. Diagnosis is made on the basis of Schwartz criteria including ECG analysis, the presence of syncope, deafness or slow heart rate
  • Andersen-Tawila syndrome - inherited autosomal dominant
  • Romano-Ward syndrome - inherited autosomal dominant

Find out more: Cardiac channelopathies: causes, types, symptoms, treatment

Long QT syndrome - symptoms and diagnosis

Such a disturbance of the electrical activity of the ventricles may not cause any symptoms, however, if there is a family history of sudden cardiac death or the syndrome of long QT interval, diagnostics in this direction is necessary. The most characteristic are fainting with convulsions or sudden cardiac arrest caused by emotions, exertion or noise. This is most often the first time it happens in children, and these episodes tend to recur. People with Andersen-Tawil syndrome also experience changes in appearance, such as palate defects or short stature.

Survival in people with LQTS is worse if they experience multiple syncope (loss of consciousness), cardiac arrest, significant QT prolongation, symptoms at a very young age, or family history of sudden cardiac death.

The diagnosis is made not only on the basis of the analysis of the ECG record, symptoms, but also the genetic test, the latter largely determines the further management and prognosis. Unfortunately, the ability to study the genes responsible for this disease is limited and costly. Due to the multitude of mutations that can eat themcause, it is necessary to consult a doctor - geneticist, who, after analyzing all symptoms, will indicate which mutation should be looked for.

Before the diagnosis of congenital long QT syndrome is made, it is necessary to exclude the acquired causes of this electrical dysfunction: electrolyte disturbances (sodium, potassium, magnesium), drug effects, and in the case of syncope, diagnostics of other possible causes (including neurological).

Long QT syndrome - treatment

The most important thing is to actively search for people at risk, that is, those who have a sick relative or a sudden cardiac death has occurred in the family. If a diagnosis is made, the main goal of treatment is to avoid situations that are conducive to the occurrence of arrhythmias:

  • avoiding drugs that prolong the QT interval (there are many of these drugs, the list is available at https://crediblemeds.org)
  • avoiding exercise
  • avoiding situations leading to electrolyte disturbances: diarrhea, vomiting
  • elimination of sudden sounds that may cause arrhythmia: alarm clock, bell

In addition, pharmacotherapy with drugs influencing nerve conduction and reducing the heart rate is necessary. In the case of fainting, cardiac arrest or ventricular tachycardia despite pharmacotherapy, but also if a particularly dangerous mutation has been found in asymptomatic patients, a cardioverter-defibrillator is implanted, which interrupts the occurring arrhythmias. In a few patients, sympathetic denervation of the heart is performed.

Bow. Maciej GrymuzaA graduate of the Faculty of Medicine at the Medical University of K. Marcinkowski in Poznań. He graduated from university with an over good result. Currently, he is a doctor in the field of cardiology and a doctoral student. He is particularly interested in invasive cardiology and implantable devices (stimulators).

Category:

Cardiology