Long QT syndrome (LQTS) is a heart rhythm disorder that can potentially cause fast, chaotic heartbeats. The rapid heartbeats, caused by changes in the part of your heart that causes it to beat, may lead to fainting. In some cases, your heart’s rhythm may beat so erratically that it can cause sudden death.

You can be born with a genetic mutation that puts you at risk of long QT syndrome. In addition, more than 50 medications, many of them common, may cause long QT syndrome. Medical conditions, such as congenital heart defects, also may cause long QT syndrome.

Long QT syndrome is treatable. You may need to limit your physical activity, avoid certain medications that can cause the condition or take medications to prevent a chaotic heart rhythm (arrhythmia). Some people with long QT syndrome also need an implantable device to control the heart’s rhythm and to prevent against sudden death.

About half those with long QT syndrome don’t have any signs or symptoms. They may be aware of their condition only from results of an electrocardiogram (ECG) performed for an unrelated reason, because they have a family history of long QT syndrome or because of genetic testing results.

For people who do experience signs and symptoms of long QT syndrome, the most common symptoms include:

  • Fainting. This is the most common sign of long QT syndrome. In people with long QT syndrome, fainting spells (syncope) are caused by the heart temporarily beating in an erratic way. These fainting spells may happen when you’re excited, angry, scared, or during exercise. Fainting in people with long QT syndrome can occur without warning, such as losing consciousness after being startled by a ringing telephone. Signs and symptoms that you’re about to faint include lightheadedness, heart palpitations or irregular heartbeat, weakness and blurred vision. If you think you’re about to faint, sit or lie down and tell someone near you about your symptoms. However, in long QT syndrome, such warning signs before fainting are unusual.
  • Seizures. If the heart continues to beat erratically, the brain becomes increasingly deprived of oxygen. This can then cause generalized seizures. In fact, some people with long QT syndrome have been misdiagnosed as having a seizure disorder and have even been treated with anti-epileptic medications.
  • Sudden death. Normally, the heart returns to its normal rhythm. If this doesn’t happen spontaneously and paramedics don’t arrive in time to convert the rhythm back to normal with an external defibrillator, sudden death will occur.

Signs and symptoms of inherited long QT syndrome may start during the first months of life, or as late as middle age. Most people who experience signs or symptoms from long QT syndrome have their first episode by the time they’re age 40. Most LQTS-related deaths occur in people ages 11 to 30.

Rarely, signs and symptoms of long QT syndrome may occur during sleep or arousal from sleep. Some doctors believe that inherited LQTS-causing mutations likely explain about 10 percent to 15 percent of sudden infant death syndrome (SIDS).

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

After each heartbeat, your heart’s electrical system recharges itself in preparation for the next heartbeat. In long QT syndrome, however, your heart muscle takes longer than normal to recharge between beats (a process known as repolarization). This electrical disturbance can be seen on an electrocardiogram (ECG).

An electrocardiogram (ECG) measures electrical impulses as they travel through your heart. Patches with wires attached to your skin measure these impulses, which are displayed on a monitor or printed on paper as waves of electrical activity.

An ECG measures electrical impulses as five distinct waves. Doctors label these five waves using the letters P, Q, R, S and T. The waves labeled Q through T show electrical activity in your heart’s lower chambers.

The space between the start of the Q wave and the end of the T wave (QT interval) corresponds to the time it takes for your heart to contract and then refill with blood before beginning the next contraction. In other words, the QT interval refers to the length of time it takes cells in your heart’s lower chambers to electrically discharge and then recharge.

By measuring the QT interval, doctors can tell whether it occurs in a normal amount of time. If it takes longer than normal, it’s called a prolonged QT interval.

Long QT syndrome results from abnormalities in the heart’s electrical recharging system. However, the heart’s structure is normal. Abnormalities in your heart’s electrical system may be inherited or acquired due to an underlying medical condition or a medication.

Inherited long QT syndrome

At least 12 genes associated with long QT syndrome have been discovered so far, and hundreds of mutations within these genes have been identified. Mutations in three of these genes account for about 75 percent of long QT syndrome. Doctors have described two forms of inherited long QT syndrome:

  1. Romano-Ward syndrome. This more common form occurs in people who inherit only a single genetic variant from one of their parents. This type of long QT syndrome affects about one in 2,500 people.
  2. Jervell and Lange-Nielsen syndrome. Signs and symptoms of this rare form usually occur earlier and are more severe than in Romano-Ward syndrome. It’s seen in children who are born deaf and have long QT syndrome because they inherited genetic variants from each parent.

Additionally, scientists have been investigating a possible link between SIDS and long QT syndrome and have discovered that about 10 percent to 15 percent of babies with SIDS had a genetic defect or mutation for long QT syndrome.

Acquired long QT syndrome

More than 50 medications, many of them common, can lengthen the QT interval in otherwise healthy people and cause a form of acquired long QT syndrome known as drug-induced long QT syndrome.

Medications that can lengthen the QT interval and upset heart rhythm include certain antibiotics, antidepressants, antihistamines, diuretics, heart medications, cholesterol-lowering drugs, diabetes medications, as well as some antifungal and antipsychotic drugs.

People who develop drug-induced long QT syndrome may also have some subtle genetic defects in their hearts, making them more susceptible to disruptions in heart rhythm from taking drugs that can cause prolonged QT intervals.

People at risk of long QT syndrome include:

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

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

People with low potassium, magnesium or calcium blood levels — such as those with the eating disorder anorexia nervosa — may be susceptible to prolonged QT intervals. Potassium, magnesium and calcium are all important minerals for the health of the heart’s electrical system.

Treatment for inherited long QT syndrome can involve medications, medical devices, surgery or lifestyle changes. The goal of treatment is either to prevent the long QT heart from ever beating out of control or to prevent sudden death.

It’s often possible to eliminate drug-induced long QT syndrome simply by switching medications, with your doctor’s direction. Some people, however, may need additional treatment. Medications used to treat long QT syndrome include:

  • Beta blockers. Examples of this heart drug include nadolol (Corgard) and propranolol (Inderal). These drugs slow the heart rate and prevent the dangerously fast heartbeats that can come about in times of stress, fear or exertion for people with long QT syndrome.
  • Potassium. Potassium is a mineral in your body, derived from your diet, that’s important for the health of your heart’s electrical system. Potassium supplements may improve the heart’s recharging system and may be helpful for people with certain forms of long QT syndrome.

Your doctor may suggest treatment for long QT syndrome even if you don’t experience frequent signs or symptoms of the disorder.

If you do need treatment, take the medications your doctor prescribes for long QT syndrome as directed. While medications won’t cure the condition, they provide some protection against potentially fatal disruptions of your heart rhythm. You may need to take a medication such as a beta blocker indefinitely.

Your doctor may consider two other treatments for you:

  • A pacemaker or implantable cardioverter-defibrillator (ICD). These devices can monitor for and, if necessary, stop a potentially fatal arrhythmia. Each device is implanted under the skin of your chest and will correct your heart’s rhythm if it detects a disrupted heart rhythm.
  • Left-sided sympathetic denervation surgery. In this procedure, specific nerves in your chest are surgically cut. These nerves are part of the body’s sympathetic nervous system, which controls automatic functions in the body including regulation of heart rhythm. This surgery is generally reserved for people considered at high risk of sudden death.

In addition to medications or surgery, your doctor will likely recommend lifestyle changes to reduce your symptoms. These could include avoiding strenuous exercise or contact sports, reducing loud, startling noises, and staying away from situations that could make you excited or angry.

If your symptoms are mild or don’t occur very often, your doctor may recommend only lifestyle changes as treatment for your condition.

Source: MayoClinic.com