Long QT Syndrome
Long QT syndrome (LQTS) is a disorder of the heart's electrical activity that may cause sudden, uncontrollable, and potentially fatal heart rhythm (called an arrhythmia) in response to exercise or stress.EKG (electrocardiogram). An EKG is a test that detects and records the electrical activity of the heart. The QT interval, recorded on the EKG, corresponds to the time during which the lower chambers of your heart (the ventricles) are triggered to contract and then build the potential to contract again.
The timing of the electrical activity of the heartbeat is complex and carefully controlled by the body. Normally the QT interval of the heartbeat lasts about a third of each heartbeat cycle on the EKG. But in people with LQTS, the QT interval lasts longer than normal, which can upset the careful timing of the heartbeat and trigger a dangerous, irregular rhythm.
- Jervell and Lange-Nielsen syndrome
- Romano-Ward syndrome
There are seven inherited types of LQTS, numbered 1 through 7. To figure out your LQTS type, your doctor will consider genetic test results, the types of situations that trigger an irregular heartbeat, and how the condition responds to medications.
On the surface of each muscle cell in the heart are tiny pores called ion channels. Ion channels open and close to let electrically charged sodium, calcium, and potassium atoms (ions) flow into and out of the cell. This generates the electrical activity of the heart.
This activity causes each heart cell to contract. Normally, the electrical activity spreads from one heart cell to the next in an orderly and coordinated way to allow the heart to pump blood. During each normal heartbeat, the muscle cells in the upper chambers of the heart, the atria, contract. The contraction pumps blood from the atria to the ventricles. Then the muscle cells in the ventricles contract, pumping blood from the ventricles to the lungs and the rest of the body. This coordinated contraction of the atria and ventricles represents one normal heartbeat.
In people who have LQTS, problems with the ion channels in the heart cells may disrupt the timing of the electrical activity in the ventricles. The ion channels may not work properly, or there may be too few of them. In this situation, the heart may suddenly develop a fast and abnormal heart rhythm that can be life threatening.
Emotional stress or physical exercise (especially swimming) that makes the heart beat faster tends to trigger irregular heart rhythms in LQTS 1. In LQTS 2, irregular rhythms may be triggered by surprise or other extreme emotions. In LQTS 3, a low heart rate during sleep may be the trigger for an irregular heart rhythm.
Acquired, or noninherited, LQTS may be brought on by certain medicines and other medical conditions.
Signs and Symptoms
Patients with LQTS are prone to developing a sudden and dangerous arrhythmia. Symptoms or signs of the arrhythmias that people with LQTS tend to have often first appear during childhood and include:
- Unexplained fainting, which may occur when you're under physical or emotional stress. Some people will have a fluttering feeling in their chest before they faint.
- Unexplained seizures, which may be mistaken for an epileptic seizure. In children, fainting may be seen as a hysterical reaction to a stressful situation.
- Unexplained drowning or near drowning. This may be due to fainting while swimming.
- Unexplained sudden cardiac stoppage or death. People who have sudden cardiac arrest will die within minutes unless they receive treatment. Most people who experience sudden cardiac arrest die. In about 1 out of 10 patients, sudden cardiac arrest or death is the first sign of LQTS.
Often people with LQTS 3 will develop an irregular heartbeat during sleep. This may cause them to have noisy gasping while sleeping.
Inherited Long QT Syndrome
Faulty genes that control the production of certain types of ion channels in your heart cells cause inherited long QT syndrome (LQTS). These LQTS genes may cause the body to produce too few ion channels or ion channels that don't work as they should, or both.
There are seven known types of inherited LQTS (types 1 though 7). The most common types of inherited LQTS are types 1, 2, and 3. Some LQTS types stem from faulty or lacking potassium ion channels, while others are due to faulty or lacking sodium channels.
If you have LQTS 1 and LQTS 2, the flow of potassium ions through the ion channels in your heart cells isn't normal, which may cause problems during periods of exercise or emotional stress.
If you have LQTS 3, the flow of sodium ions through ion channels in your heart cells isn't normal, which also may trigger a rapid and uncontrollable heart rhythm that can result in death. In LQTS 3, problems usually develop when your heart beats slower than normal, such as during sleep.
Noninherited Long QT Syndrome
Acquired, or noninherited, LQTS may be brought on by certain medicines and other medical conditions. Side effects from certain medicines are the most common cause of noninherited LQTS.
Medication-Induced Long QT Syndrome
Presently, more than 50 medicines have been recognized to cause LQTS. Some of the commonly used medicines that may cause LQTS include:
- Antihistamines and decongestants
- Diuretics (pills that remove excess water from your body)
- Cholesterol-lowering medicines and some diabetes medicines
Some people with medication-induced LQTS may also have an inherited form of the syndrome that doesn't cause symptoms unless they take certain medicines that lengthen the QT interval or lower potassium levels in the blood. This is sometimes called silent LQTS.
Other Causes of Acquired Long QT Syndrome
Excessive diarrhea or vomiting that causes a major loss of potassium or sodium ions from the bloodstream may cause LQTS. The syndrome lasts until the levels of these ions in the blood return to normal. The eating disorder anorexia nervosa and certain thyroid disorders may cause a drop in potassium ion levels in the blood, causing LQTS.
Cardiology is the medical specialty dealing with the heart; cardiologists are physicians who diagnose and treat long QT syndrome (LQTS). The diagnosis of LQTS usually rests on a combination of EKG results, medical history and physical exam findings, and genetic test results.
An EKG is a simple test that detects and records the electrical activity of the heart. This test may reveal a long QT interval and when an EKG is done for another suspected heart problem. The test may also need to be done during exercise (a so-called "stress test").
Medical History and Physical Exam
Relevant findings that may become apparent during an interview with the patient or a physical exam include unexplained fainting, reports of a fluttering feeling in the chest, or loud gasping during sleep. Knowledge of whether any family members was diagnosed with or shows signs of LQTS may also help in making or refuting the diagnosis.
Genetic blood tests can detect some forms of inherited LQTS. Genetic blood tests are usually also suggested for family members of people with LQTS, but about one-third of LQTS cases aren't detected with genetic testing. Also, as many as one-third of the people who test positive for LQTS don't have any signs or symptoms of the disorder. These people may have silent LQTS. Fewer than 1 out of 10 of these people will faint or suddenly die from an irregular heartbeat.
The goal of treating long QT syndrome (LQTS) is to prevent life-threatening, irregular heartbeats and fainting spells. Treatment isn't a cure for this condition and may not restore a long QT interval (on your EKG) to normal. But it does greatly improve survival.
Treatment recommendations are based on the type of LQTS, the likelihood of dangerous arrhythmias, and what medications are available. People who have a lower risk of complications from LQTS may want to try less aggressive treatments, such as making lifestyle changes (avoiding situations that trigger irregular heartbeats) or taking medicines. Doctors will usually only prescribe sodium channel blocker medicines for people with LQTS 3.
More aggressive treatments include:
- A surgically implanted device (such as a pacemaker or implantable cardioverter defibrillator (ICD)) that helps regulate your heartbeat
- Surgery on the nerves that regulate your heartbeat
Patients at higher risk are those who have fainted or who have developed dangerous heart rhythms from their LQTS in the past.
Avoidance of specific triggers for an irregular heartbeat is often recommended. Many people with LQTS also benefit from adding more potassium to their diets. People with LQTS also should avoid medicines that lengthen the QT interval or lower potassium blood levels.
Beta blocker heart medicines prevent the heart from beating faster in response to physical or emotional stress. Most people with LQTS are treated with beta blockers. Doctors may suggest that people with LQTS 3 take sodium channel blocker medicines, such as mexiletine. These make sodium ion channels less active.
Pacemaker or Implantable Cardioverter Defibrillator
These are surgically implanted devices that monitor the heart rhythm and deliver electrical currents to the heart when they detect an abnormal heart rhythm. Surgeons implant pacemakers and ICDs in the chest or belly with a minor procedure.
People at high risk of death from LQTS are sometimes treated with surgery in which the nerves that prompt the heart to beat faster in response to physical or emotional stress are cut. This helps to keep the heart beating at a steady pace and decreases the chances of developing dangerous heart rhythms in response to stress or exercise.
Chances of Developing Long QT Syndrome
Long QT syndrome (LQTS) is a rare condition. Experts suspect that about 1 in 7,000 people has LQTS. But no one knows for sure, because LQTS often goes undiagnosed.
LQTS causes about 3,000 to 4,000 sudden deaths in children and young adults each year in the United States. Unexplained sudden death in children is rare. But when it does occur, LQTS often is the cause.
Inherited LQTS usually is first detected during childhood or young adulthood. Half of all people with LQTS experience their first irregular heartbeat by the time they're 12 years old, and 90 percent by the time they reach 40 years old. Rarely is inherited LQTS first diagnosed in someone after age 40. In boys with LQTS, the QT interval often returns toward normal after puberty, and the risk of fainting and sudden cardiac arrest decreases.
LQTS is more common in women than men. Women who have LQTS are more likely to experience fainting or sudden death from the condition during menstruation and shortly after giving birth. LQTS also is common in children born deaf. This is because the same genetic abnormality that affects hearing also affects the working of ion channels in the heart.
Living With Long QT Syndrome
Long QT syndrome (LQTS) is usually a lifelong condition. The risk of developing an irregular heartbeat that leads to fainting or sudden cardiac arrest may lessen with increasing age, but the risk never disappears.
Common recommendations include:
- Avoiding things that trigger an abnormal heart rhythm
- Advising friends, colleagues, and family members of the condition so that they can help if needed
- Having a plan in place for episodes of irregular heartbeat
More than half the people who have an untreated, inherited form of LQTS die within 10 years. But for many people with LQTS, lifestyle changes and medical treatments can help prevent dangerous complications and lengthen life expectancy. Some of these changes include:
- Avoiding strenuous physical activity or startling noises
- Adding more potassium to the diet
- Taking heart medicines called beta blockers, which are very effective at preventing sudden cardiac arrest
- Having an implantable device, such as a pacemaker or implantable cardioverter defibrillator, that helps control abnormal heart rhythms
- ↑ Napolitano C, Priori SG, Schwartz PJ, et al. Genetic testing in the long QT syndrome: development and validation of an efficient approach to genotyping in clinical practice. JAMA. 2005 Dec 21;294(23):2975-80. Abstract | Full Text | PDF
- ↑ Paavonen KJ, Swan H, Piippo K, et al. Response of the QT interval to mental and physical stress in types LQT1 and LQT2 of the long QT syndrome. Heart. 2001 Jul;86(1):39-44. Abstract | PDF
- ↑ Morissette P, Hreiche R, Turgeon J. Drug-induced long QT syndrome and torsade de pointes. Can J Cardiol. 2005 Aug;21(10):857-64. Abstract
- ↑ Khan IA. Long QT syndrome: diagnosis and management. Am Heart J. 2002 Jan;143(1):7-14. Abstract
- ↑ Goldenberg I, Moss AJ. Long QT syndrome. J Am Coll Cardiol. 2008 Jun 17;51(24):2291-300. Abstract
- Arrhythmia (Diseases and Conditions Index)
- Electrocardiogram (Diseases and Conditions Index)
- Implantable Cardiac Defibrillator (Diseases and Conditions Index)
- Pacemaker (Diseases and Conditions Index)
- Sudden Cardiac Arrest (Diseases and Conditions Index)
- Long QT Syndrome (MedlinePlus)