What Is Long QT Syndrome?

Long QT syndrome is an alteration of the electrical mechanism of the heart. We'll explain what it is and what implications it may have.
What Is Long QT Syndrome?
Diego Pereira

Reviewed and approved by the doctor Diego Pereira.

Written by Carmen Martín

Last update: 22 May, 2023

Long QT syndrome (LQTS) is a heart condition. It consists of an alteration of the heart’s electrical system, which causes its rhythm to become fast and chaotic.

The heart is the organ in charge of pumping oxygenated blood to all parts of the body. Therefore, when it doesn’t beat properly, the blood flow to other organs is also altered.

That’s why long QT syndrome can lead to seizures, fainting, and even death.

The problem is that this condition can have multiple causes, ranging from medical or metabolic to genetic. In this article, we’re going to explain everything you need to know about the syndrome and why it occurs.

What is Long QT syndrome?

Long QT syndrome is a disorder of the heart’s electrical activity. As explained in an article by the Nemours Foundation, this disease makes it difficult for the heart to beat normally.

The structure of the heart isn’t affected. In order to understand this syndrome, it’s essential to first understand how the heart works. With each beat, the organ pushes a sufficient amount of blood to the tissues. The beats are produced by a series of electrical changes that take place in the heart cells.

This electrical system allows the heart to beat rhythmically and at an appropriate rate so that the chambers can fill well with blood. What happens in long QT syndrome is that, due to the electrical disturbance, the heart takes longer to recover between beats.

As a result, the heart chambers fail to fill completely with blood. In addition, the rhythm is disturbed and the beats become increasingly irregular.

Causes of long QT syndrome

Long QT syndrome can have multiple causes. Generally speaking, it’s divided into two main types: congenital and acquired. The former, as its name suggests, is present from birth. In the following sections, we’ll explain each one in particular.

Congenital causes

Congenital long QT syndrome is due to a genetic alteration. Numerous genes have been identified that could be involved in the pathology, as summarized in an article in EMC-Pediatrics.

In a simplified way, a distinction is made between those causes transmitted by autosomal dominant inheritance and the others, of recessive inheritance. Cases of autosomal recessive inheritance are usually more severe and tend to be associated with deafness.

Mutación del sindrome QT largo
The congenital form of this disease is due to DNA mutations.

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Acquired long QT syndrome

Acquired long QT syndrome is much more common than congenital. The main cause of its occurrence is medication. There is a multitude of drugs that can prolong the QT segment, among which we find:

  • Antipsychotics
  • Antibiotics such as azithromycin
  • Antiarrhythmics

On the other hand, electrolyte imbalances are also a significant cause. The syndrome usually appears when the levels of potassium, calcium, or magnesium in the blood drop.

During the COVID-19 pandemic, the syndrome was associated with SARS-CoV-2 infection.

What symptoms does it produce?

As explained by Mayo Clinic specialists, long QT syndrome doesn’t always present symptoms. In fact, many cases are detected by testing for another reason or suspected by family history.

However, there is also a very high percentage of people who do have symptoms. The most common symptom is fainting or syncope. It’s common for these people to faint during exercise or in the face of strong emotions. Sometimes there are pre-fainting signs such as palpitations, lightheadedness, and weakness.

Other patients have seizures. In some cases, if electrical activity does not return to normal, death may even occur.

The symptoms associated with long QT syndrome can occur at any time of the day, even during sleep. In most cases, this disease makes its debut after the age of 40 and is very rare before that decade, as reported in Gene Reviews.

Complications of long QT syndrome

One of the most common complications is called torsade de pointes. This is a type of ventricular arrhythmia that causes the ventricles to beat uncontrollably and rapidly. This results in the heart being unable to pump blood normally. As a result, the cerebral blood supply may fail.

Ventricular fibrillation is another typical complication of this syndrome. It’s one of the most dangerous arrhythmias; if not defibrillated, it leads to death. In addition, fainting can lead to falls or other serious accidents.

How is long QT syndrome diagnosed?

Diagnosis of long QT syndrome, as noted in a Texas Heart Institute article, requires a number of additional tests. The electrical activity of the heart must be observed to confirm the alteration.

For this purpose, the most commonly used test is the electrocardiogram. This records the electrical activity of the heart. It can be used to determine whether the QT interval is lengthened.

The Q wave refers to ventricular depolarization and the T wave to repolarization.

In some cases, a Holter study is performed. This is a test that allows the heart rhythm to be monitored for 24 hours or more. This allows you to see if the syndrome occurs at any time during the day.

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How can it be treated?

Long QT syndrome is usually treated as soon as it’s detected. Otherwise, it increases the risk of sudden death. In addition, in many cases, lifestyle or lifestyle changes are enough to reduce the likelihood of a fatal event.

When the cause is a drug, it’s most often withdrawn or replaced with another medication. If it’s an electrolyte disorder, it will be corrected promptly. As specified in a 2022 report, the combination of certain drugs prescribed for vomiting plus the loss of electrolytes from the vomiting itself is a high-risk combination for the syndrome to occur.

Medications used to treat long QT syndrome

There are a number of drugs that can be used to protect patients with long QT syndrome. The most commonly used are beta-blockers, such as propranolol or nadolol. These drugs help to slow the heart rate and reduce episodes of QT prolongation.

In other patients, mexiletine is used. It’s usually combined with a beta-blocker. It reduces the risk of seizures and fainting.

Medicamento para el sindrome QT largo
Beta-blockers are the drugs of choice in this clinical condition.

Surgery or other procedures

In addition to medical treatment, long QT syndrome may benefit from other interventions. One of these is surgery. As a study in the Revista Española de Cardiología explains, the surgery consists of sympathetic denervation of the left heart.

Therefore, this is a technique that attempts to remove the innervation of the sympathetic nervous system from that part of the heart. The sympathetic nervous system is one of the regulators of cardiac rhythm. This prevents the heart from racing too fast and reduces the risk of sudden death.

This treatment is usually reserved for cases that do not respond well to drugs. Another option is to implant a defibrillator or pacemaker. These are devices that control the heart’s rhythm. They deliver small electrical shocks when the organ fails.

Long QT syndrome increases a person’s risk of sudden death

Long QT syndrome is a disturbance in the heart’s electrical system. It causes the heart to beat in an uncontrolled, arrhythmic manner on occasion. Many people may remain asymptomatic for long periods of time.

If a person has repeated unexplained fainting spells or seizures, it’s important to consult a physician. Family history should also always be considered when looking for a diagnosis.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.