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What is it about ?
The heart is made up of two atria and two ventricles that contract regularly due to electrical activity from the heart. This electrical activity can be assessed using an electrocardiogram (ECG). The electrical activity of the heart is thus made up of a series of waves.
During the contraction of the atria, the ECG records the P wave. It is normally followed by the QRS complex, which is recorded during the contraction of the ventricles. When the ventricles relax, the ECG shows a T wave. In healthy people, the time between the ventricles contracting and relaxing cannot be too long. This delay is called the QT interval because it is measured from the start of the QRS complex, i.e. the Q point, to the end of the T wave.
How to recognize it?
If the QT interval is too long, there is a risk of serious life-threatening heart rhythm disturbances. Too long a QT interval causes palpitations, fainting, or even sudden death. Seizures sometimes resemble epileptic fits. These heart rhythm disturbances can be caused by special circumstances, such as sudden physical exertion or strong emotion.
In some people, having too long a QT interval is due to a genetic problem, more specifically an error (mutation) in the genetic material of the cells of the heart. This error is responsible for a disturbance in the electrical activity of the heart. Long QT syndrome is not always congenital, but it can be due to certain medications or other functional disorders of the body.
The two most well-known genetic diseases that cause long QT syndrome are Romano-Ward syndrome and Jervell and Lange-Nielsen syndrome. In Romano-Ward syndrome, a mutation in only one of the two chromosomes is enough to cause the disease, while in Jervell and Lange-Nielsen syndrome, each of the two chromosomes inherited from the parents contains the mutation, and the disease is then associated with congenital deafness.
In the genetic variant, seizures already appear in infancy, and their frequency increases as the child grows. A first fainting occurs most often around the age of 11 in boys and around the age of 16 in girls. In adulthood, women generally have more symptoms than men. Sometimes symptoms go unnoticed, and the disease only manifests itself when taking drugs that affect the QT interval.
What is its frequency?
Long QT syndrome is relatively rare. It is more common in people who have heart disease.
Romano-Ward syndrome occurs in 1 in 3,000 people, and Jervell and Lange-Nielsen syndrome, which is rarer, occurs in 1 in a million people.
How is the diagnosis made?
Long QT syndrome is seen on the ECG.
The QT interval is always related to the heart rate. This is because the limits of a normal QT interval depend on heart rate. The corrected QT interval (QTvs), which is calculated according to Bazett’s formula, cannot exceed 470 milliseconds in women and 450 milliseconds in men.
If the QT interval is too long, the doctor refers the person to a cardiologist (specialist in heart disease). If a genetic condition is suspected, the doctor will order a genetic examination.
What can you do ?
The doctor will give you information about the circumstances that may cause you to have a disturbed heart rhythm. Follow his advice carefully. In most cases, competitive sport is prohibited. Recreational sporting activities are generally permitted. Certain professions are not recommended due to risk factors.
Some medicines can no longer be taken. Also warn other doctors who may be required to treat you.
What can the doctor do?
In hereditary long QT syndrome, a beta blocker will often be prescribed first to slow the heart rate. If this is not enough or if the result is not satisfactory, or in the event of sudden death in the family following life-threatening arrhythmias, the placement of a pacemaker or a Automatic implantable defibrillator (ICD).
In the case of acquired (non-inherited) long QT syndrome, the emphasis is on treating a possible underlying heart disease and prohibiting drugs that may prolong the QT interval. The electrolyte balance in the body should also be carefully considered.
Sources
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