Generality
Long QT, or long QT syndrome, is a rare cardiac condition, which leads to an increase in the depolarization / repolarization times of the ventricles. In other words, those suffering from long QT syndrome have a heart whose ventricles take longer than usual to relax after a first contraction, and to prepare for the next contraction.
Long QT can be a hereditary or acquired condition.
When present, the typical symptoms consist of: syncope, palpitations and episodes of epilepsy.
The diagnostic examination that allows its identification is the electrocardiogram: the name "long QT" is linked to a particular characteristic of the electrocardiographic trace.
The therapy varies depending on whether the long QT is hereditary or acquired.
Anatomical and functional recall of the heart
The heart is an unequal organ, which can be divided into four cavities (the right atrium, the left atrium, the right ventricle and the left ventricle) and composed of a very particular muscle tissue: the myocardium .
The particularity of the myocardium is its ability to generate and autonomously conduct the nerve impulses for the contraction of the atria and the ventricles .
The source of these impulses, which are comparable to electrical signals, resides at the level of the right atrium of the heart and is called the atrial sinus node .
The atrial sinus node has the task of scanning the right frequency of contraction of the heart ( heart rate ), in such a way as to guarantee a normal heart rhythm.
The normal heart rate is also known as sinus rhythm .
To best succeed in its contractile action, the atrial sinus node uses some sorting centers for electrical impulses. These centers are the atrioventricular node, the bundle of His and the Purkinje fibers, which together form, together with the atrial sinus node, the so-called electrical conduction system of the heart .
Figure: in the electrical conduction system of the heart, the atrial sinus node constitutes the main pedestal center (marker because it scans the heart rate); the atrioventricular node, the His bundle and the Purkinje fibers, on the other hand, represent the secondary marker centers, as they depend on the atrial sinus node.
What is long QT?
Long QT, or long QT syndrome, is a rare cardiac condition that arises due to an abnormal conduction of electrical signals along the myocardium, and which can lead to the onset of cardiac rhythm disorders ( arrhythmias ).
ORIGIN OF THE NAME
The doctors coined the term "long QT" in reference to the particular aspect of the electrocardiographic tracing of people with long QT syndrome (see the chapter dedicated to diagnosis).
Causes
Atriums and ventricles of the heart contract at different times.
After each contraction - a phenomenon that physiologists call depolarization - they need a certain amount of time to respond to another contraction. During this time, the muscle fibers that make up the atria and the ventricles relax.
If in physiology the contraction is known as depolarization, relaxation is called repolarization .
In healthy people from the cardiac point of view, the depolarization and repolarization of the atria and ventricles take place with a certain timing and this timing represents a reference that indicates normality.
People with long QT present an alteration of this timing: in this case, the process of depolarization / repolarization of the ventricles takes longer than necessary, therefore it is lagging behind the normal one.
The possible cause of arrhythmias in individuals with long QT is precisely this delay in the depolarization / repolarization of the ventricles.
WHAT HAS THE DELAY IN THE REPOLARIZATION: INFORMATION ON PHYSIOLOGY
Premise: myocardial muscle cells have small pores on their membrane, called ion channels, which allow the passage of sodium, calcium and potassium ions.
The passage of these ions from inside to outside the cells and vice versa is what allows the contraction and relaxation of the muscle fibers.
Physiologists have long studied what is the cellular mechanism that determines the delay in the depolarization / repolarization of the ventricles and have highlighted two possible alternative causes:
- In most cases, the delay is subsequent to a malfunction of the ion channels for potassium .
- In a small number of cases, the delay is the consequence of a malfunction of the sodium channels .
QT LONG HEREDITARY
Numerous scientific studies have shown that long QT is usually a hereditary condition, that is transmitted from one of the two parents to the progeny (the children).
According to these studies, the genes involved in the hereditary transmission of long QT would be 17, while the possible mutations (ie alterations of the genome) would be about one hundred.
The genes responsible for hereditary long QT have the task of synthesizing the proteins that make up the ion channels, based on myocardial muscle cells.
In light of this, the reader can understand why a mutation of these genes causes a malfunction of the channels that carry potassium or sodium.
The researchers identified two forms of hereditary long QT:
- Romano Ward syndrome . It is the most widespread hereditary form.
- Jervell and Lange Nielsen syndrome .
Curiosity: 75% of cases of long QT syndrome follow mutations in 3 of the 17 genes involved in the appearance of the hereditary condition of the condition.
QT LONG ACQUIRED
Long QT can also be an acquired condition, that is, developed over a lifetime, due to some triggering factor.
In the case of long QT syndrome, the triggers of the acquired form of the condition are a series of drugs (more than 75), including:
- Antibiotics
- Antidepressants and antipsychotics
- Antihistamines
- Diuretics
- Medicines for maintaining the normal heart rhythm
- Medicines for reducing blood cholesterol levels (cholesterol-lowering medicines)
- Medicines for diabetes
Doctors and experts in the field of cardiac physiology believe that people with acquired long QT possess a heart predisposed, from birth, to the development of the aforementioned condition, after the use of the listed drugs.
Moreover, this would explain why not all individuals taking the above medicines develop long QT syndrome.
RISK FACTORS
They represent a long QT risk factor:
- The fact of having one or more first-degree relatives with the inherited form of the condition.
- Taking one or more of those drugs that can cause acquired long QT.
- The presence of alterations in the blood levels of potassium and other ions.
Epidemiology
According to some statistical studies, hereditary long QT is a cardiac condition that affects one person every 2, 000 .
Symptoms and Complications
Long QT can be both asymptomatic (ie without symptoms and obvious signs) and symptomatic .
When symptomatic (minority of cases), the most common manifestations consist of fainting episodes (or syncope), palpitations and epileptic seizures.
These manifestations, especially syncope, generally appear without warning.
AGE OF INSURANCE OF LONG HEREDITARY QT
In subjects with long hereditary symptomatic QT, the age of onset of clinical manifestations varies considerably from subject to subject: in some cases, the symptoms and signs appear a few weeks after birth; in other cases, instead, during childhood or adulthood.
Many people with symptomatic hereditary QT experience the first ailments around the age of 40. The reason for this is still unclear.
COMPLICATIONS
Long QT can have two major complications, which consist of:
- The so-called " tip twist ". It is an arrhythmia, to be precise, a ventricular tachycardia. Its presence leads to a reduction in blood flow to the brain due to severe impairment of cardiac contraction.
- The onset of ventricular fibrillation . It is another arrhythmia, very serious and which profoundly alters the heart rate. Ventricular fibrillation is often the cause of a phenomenon known as sudden death .
WHEN TO REFER TO THE DOCTOR?
They should contact the doctor:
- Those who suddenly experience episodes of syncope, epilepsy and palpitations.
- Those who belong to families where the long QT occurs.
Diagnosis
During the diagnosis of long QT, both the physical examination and the medical history (anamnesis) are important.
However, for any definitive conclusion, it is necessary to resort to an electrocardiogram (ECG), as only this diagnostic test allows any doubt or uncertainty to be clarified.
IMPORTANCE OF ELECTROCARDIOGRAM
The electrocardiogram reveals the rhythm and electric activity of a heart, drawing a characteristic pattern on graph paper.
The tracing of the rhythm and electrical activity of a healthy heart has 5 relevant elements, called waves, which repeat themselves with regularity. The waves are identified with the capital letters P, Q, R, S and T.
With the help of the figure below, the reader can appreciate what the arrangement of the waves is and notice how there is a certain distance between them, identified with the term interval .
The length of an interval on the sheet of graph paper indicates the duration of this interval.
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| Standard duration of the intervals of a normal electrocardiogram: |
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It is important to emphasize that maintaining a certain distance between two waves - therefore the presence of always equal intervals - is an indication of normality in the heartbeat ; on the other hand, excessive lengthening or shortening of the same distance indicates some alteration.
In this sense, even a change in the appearance of the waves indicates that the heart is functioning abnormally.
Returning then to long QT, the ECG of a person with this cardiac condition has much longer QT intervals than the visible QT intervals on an electrocardiographic pattern of a healthy heart.
QT expresses the time of depolarization and repolarization of the ventricles.
Now, if it is true that the length of an interval indicates its duration, a QT interval longer than normal means that it lasts longer than normal and that the process of depolarization / repolarization of the ventricles is slower, delayed.
Figure: typical electrocardiogram of a person with long QT. The QT interval of a person with a healthy heart lasts between 0.37 seconds and 0.42 seconds. The QT interval of a person with long QT has a duration longer than 0.42 seconds.
Treatment
Hereditary long QT therapy involves the administration of some particular drugs and also, in some cases, the implementation of specific surgical procedures.
The acquired long QT treatment, on the other hand, consists much more trivially in interrupting the pharmacological intake that causes the cardiac anomaly. Clearly, in these situations, if the patient takes more than one potentially responsible drug, the doctor must investigate what is the precise medicine that triggers the symptoms and advise against their use.
Advice for those with long QT:
- Do not practice contact sports
- Do not perform particularly strenuous physical exercises
- Avoid stressful situations
- Avoid using instruments with surprising noises (such as alarm clocks)
- Ask your doctor for advice before taking any medicine
DRUGS AND OTHER PREPARED FOR LONG HEREDITARY QT
Hereditary long QT medications include beta blockers and mexiletine .
Furthermore, if the disorder affects the ionic potassium channels, doctors also tend to prescribe potassium supplements.
SURGERY FOR LONG HEREDITARY QT
Possible surgical interventions for long-inherited QT consist of:
- Installation of a pacemaker or implantable cardioverter defibrillator .
- The so-called left sympathetic cardiac denervation . It is a very delicate operation, which involves the removal of some nerve endings capable of modifying the heart rate. It is used to reduce the risk of sudden death.
Prognosis
The prognosis varies from patient to patient. For some, long QT is asymptomatic for life.
For other subjects, it causes serious symptoms and even death.
