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Long QT Syndrome

Definition


Disease: Long QT Syndrome Long QT Syndrome
Category: Cardiovascular diseases
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Disease Definition:

Long QT syndrome is a heart rhythm disorder that could potentially cause fast, chaotic heartbeats. A person could faint due to the rapid heartbeats that are caused by changes in the part of the heart that causes it to beat. Sometimes, the heart rhythm could beat so erratically that it could cause sudden death.

People may be born with a genetic mutation that put them at risk of long QT syndrome. Also, long QT syndrome could be caused by more than 50 medications, many of which are common. Medical conditions could also cause this syndrome such as congenital heart defects.

Long QT syndrome could be treated. To prevent a chaotic heart rhythm (arrhythmia), people may need to take medications, limit their physical activity and avoid certain medications that cause the condition. To prevent against sudden death or to control the heart's rhythm, some people with long QT syndrome may need an implantable device.

Work Group:


Prepared by: Scientific Section

Symptoms, Causes

Symptoms:

Usually, about half the people with long QT syndrome don't experience any signs or symptoms. These people could only be aware of their condition due to an electrocardiogram (ECG) performed for an unrelated reason because of genetic testing results or because they have a family history of long QT syndrome.

Some of the most common symptoms for people who do experience them may include:

Fainting:
The most common sign of long QT syndrome is fainting. When the heart of someone with long QT syndrome temporarily beats in an erratic way, it causes him/her to have fainting spells. During exercise or when they’re angry, excited or scared, these fainting spells may occur. Some people may lose consciousness after being startled by a ringing telephone, so, fainting in people with long QT syndrome may occur without warning.
Blurred vision, heart palpitations, irregular heartbeat, lightheadedness and weakness are some of the signs and symptoms indicating that the person is about to faint. A person should sit or lie down and tell someone near them about their symptoms in case they think that they’re about to faint. However, in long QT syndrome, these warning signs before fainting might not happen.

Seizures:
The brain will become increasingly deprived of oxygen in case the heart continues to beat erratically. This could cause generalized seizures. As a matter of fact, some people with long QT syndrome have been treated with anti-epileptic medications because they have been misdiagnosed as having a seizure disorder.

Sudden Death:
Normally, the heart returns to its normal rhythm. However, sudden death could occur in case the heart doesn't return to its normal rhythm spontaneously and paramedics don't arrive in time to convert the rhythm back to normal with an external defibrillator.
The signs and symptoms of inherited long QT syndrome could start as early as the first months of life or as late as middle age. By the time they aged 40, most people who experience signs or symptoms from long QT syndrome will have their first episode. Most deaths that are related to long QT syndrome occur in people between the ages of 11 and 30.

In some rare cases, during sleep or sleep arousal, signs and symptoms of LQTS may occur. It is believed that the mutations that cause inherited LQTS explain about 10 to 15% of SIDS (sudden infant death syndrome).

Causes:

To circulate blood throughout the body, the heart beats about 100,000 times a day. The chambers of the heart contract and relax to pump blood. These actions are controlled by electrical impulses that are created in the sinus node, which is a group of cells in the upper right chamber of the heart. These impulses travel through the heart, causing it to beat.

The heart's electrical system recharges itself after each heartbeat in preparation for the next heartbeat. However, if someone has LQTS, their heart muscle will take longer than normal to recharge between beats, which is known as repolarization. An electrocardiogram (ECG) could show these electrical disturbances.

PROLONGED QT INTERVAL:
An ECG (electrocardiogram) will measure electrical impulses as they travel through the heart. These impulses, which are displayed on a monitor or printed on paper as waves of electrical activity will be measured by patches with wires attached to the skin.
An ECG will measure these electrical impulses as five distinct waves. These waves are labeled by using the letters P, Q, R, S and T. The electrical activity in the heart's lower chambers includes the waves labeled Q through T.

The amount of time it takes for the heart to contract and then refill with blood before beginning the next contraction is referred to by the space between the start of the Q wave and the end of the T wave (QT interval). This means that the length of time it takes cells in the heart's lower chambers to electrically discharge and then recharge is referred to as the QT interval.

Measuring the QT interval allows the doctors to know if it occurs in a normal amount of time or not. The QT interval will be called a prolonged QT interval if it takes longer than normal.

Abnormalities in the heart's electrical recharging system cause long QT syndrome. These abnormalities could be either inherited or acquired due to a medication or an underlying medical condition. However, in long QT syndrome, the structure of the heart is normal.

INHERITED LONG QT SYNDROME:
So far, 12 genes have been discovered that are associated with long QT syndrome, and hundreds of mutations have been identified within these genes. About 75% of long QT syndrome is caused by mutations in three of these genes.
Here are two forms of inherited long QT syndrome:

Romano-Ward syndrome:
When people inherit only a single genetic variant from one of their parents, this more common form occurs. About one in 2,500 people are affected by this form of long QT syndrome.

Jarvell and Lange-Nielsen syndrome:
The signs and symptoms of this rare form are more severe than in Romano-Ward syndrome, and they occur earlier. When children inherit genetic variants from each parent, they may be born deaf and have long QT syndrome.
There's a possible link between SIDS and long QT syndrome, because about 10 to 15% of babies with SIDS have been found to have a genetic defect or mutation for long QT syndrome.


ACQUIRED LONG QT SYNDROME:
 Drug-induced long QT syndrome could be caused by more than 50 medications, many of which are common. These medications could lengthen the QT interval in otherwise healthy people and cause a form of acquired long QT syndrome.

Some of the medications that could lengthen the QT interval and upset heart rhythm include:

 

  • Cholesterol-lowering drugs
  • Antihistamines
  • Some antifungal drugs
  • Certain antibiotics
  • Diabetes medications
  • Some antipsychotic medications
  • Heart medications
  • Antidepressants
  • Diuretics


People will be more susceptible to disruptions in their heart rhythm from taking drugs that can cause prolonged QT intervals in case they have developed drug-induced long QT syndrome and also have some subtle genetic defects in their heart.

People who are at risk of long QT syndrome may include:

  • Relatives of persons with known long QT syndrome
  • Children, teenagers and young adults with unexplained fainting, unexplained near drownings or other accidents, a history of cardiac arrest, or unexplained seizures.
  • People taking medications known to cause prolonged QT intervals
  • Family members of children, teenagers and young adults with unexplained fainting, unexplained near drownings or other accidents, a history of cardiac arrest, or unexplained seizures.  


 Usually, long QT syndrome goes undiagnosed or is misdiagnosed as a seizure disorder, such as epilepsy. However, for some otherwise unexplained deaths in children and young adults, researchers believe that long QT syndrome may be responsible. For instance, the first clue to inherited long QT syndrome in a family could be the unexplained drowning of a young person.

People may be susceptible to prolonged QT intervals in case they have low potassium, magnesium or calcium blood levels, such as those with the eating disorder anorexia nervosa. For the health of the heart's electrical system, potassium, magnesium and calcium are all important minerals.

Complications

Complications:

No problems may be caused by prolonged QT intervals. However, emotional or physical stress could "trip up" a heart that is susceptible to prolonged QT intervals, and cause the rhythm of the heart to spin out of control.

A particular arrhythmia called torsades de pointes (twists of the points) may be caused by a prolonged QT interval. In this arrhythmia, the heart's ventricles beat fast and make the waves on an ECG monitor look twisted. Less blood will be pumped out from the heart when this arrhythmia occurs. This will cause a person to faint because less blood will reach the brain.

However, the heart could correct itself seconds later, and the person could regain consciousness on his/her own in case the torsades de pointes episode is short, lasting less than one minute. However, this could lead to a life-threatening arrhythmia called ventricular fibrillation in case the torsades de pointes episode persists.

The ventricles will beat so fast in ventricular fibrillation that the heart will quiver and cease pumping blood. Ventricular fibrillation could lead to brain damage and death unless the heart is shocked back into a normal rhythm by a device called a defibrillator. In young people who otherwise appear healthy, it's thought that long QT syndrome may explain some cases of sudden death.

Treatments:

Medications, medical devices, surgery or lifestyle changes may be involved in treating inherited long QT syndrome. Preventing sudden death or preventing the long QT heart from ever beating out of control will be the goal of treatment.

Usually, drug-induced long QT syndrome could be eliminated simply by switching medications with the doctor's direction. However, additional treatment may be needed for some people.

MEDICATIONS:
Some of the medications that could be used in treating long QT syndrome may include:

Beta blockers:
These medications could prevent the dangerously fast heartbeats that can come about in times of fear, exertion or stress for people with long QT syndrome. They also slow the heart rate. Some examples of these drugs include propranolol and nadolol.

Potassium:
Potassium is an important mineral for the health of the heart's electrical system. It is derived from a person’s diet. Some people with certain forms of long QT syndrome may benefit from potassium supplements, which could also improve the heart's recharging system.

Even if someone doesn’t experience frequent signs or symptoms of long QT syndrome, they may be suggested treatment.
In case someone needs treatment for long QT syndrome, they should take the prescribed medications just as the doctor has directed. These medications could provide some protection against potentially fatal disruptions of the heart rhythm; however, they don't cure the condition. Some medications such as beta blockers, may need to be taken indefinitely.

SURGICAL PROCEDURES AND MEDICAL DEVICES:
The doctor could consider two other treatments:

Left-sided sympathetic denervation surgery:
Specific nerves in the patient’s chest will be surgically cut in this procedure. These nerves are part of the body's sympathetic nervous system which controls automatic functions in the body, including regulation of heart rhythm. Usually, people who are considered to be at high risk of sudden death undergo this surgery.

A pacemaker or ICD (implantable cardioverter-defibrillator):
Each of these devices will be implanted under the skin of the chest and correct the heart's rhythm in case it detects a disrupted heart rhythm. Meaning that these devices could monitor for and, when necessary, stop a potentially fatal arrhythmia.

LIFESTYLE CHANGES:
A person will be recommended lifestyle changes in addition to medications or surgery to reduce the symptoms. Staying away from situations that could make them excited or angry, avoiding strenuous exercise or contact sports and reducing loud, startling noises are some of those lifestyle changes.
Someone may be recommended only lifestyle changes as treatment in case their symptoms are mild or don't occur very often.

Prognosis:

Not Available

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