Long QT syndrome
Long QT Syndrome (LQTS) is an abnormality of the heart's electrical system. The mechanical function of the heart is normal, however, the electrical problem is due to defects in heart muscle cell structures called ion channels. These electrical defects pre-dispose affected persons to a very fast heart rhythm called ‘Torsades de pointes’ which leads to sudden loss of consciousness (syncope) and may cause sudden cardiac death.
The syndrome gets its name from the distinctive 'signature' or shape of the wave—an unusually long interval between the 'Q' and 'T' wave points—shown on an electrocardiagram (ECG), or heart monitor. This shows how long it takes for the heart to return to 'normal' after contracting and pumping blood through the body.
This syndrome can be inherited or acquired.
Inherited Long QT Syndrome
This was first clearly described in 1957 as two variants, the autosomal-dominant Romano-Ward type and the autosomal-recessive Jervell, Lange-Nielsen type. (An autosome is a type of chromosome in the body's genetic make-up that does not determine sex.)
Acquired Long QT Syndrome
This version is most often due to the administration of medications. Some medications prolong the QT interval, so they may interfere with the heart rhythm. These include antiarrhythmic drugs, used to control heart rhythm; some anticancer drugs; some antidepressants; some migraine medications; some antipsychotic medications used to treat schizophrenia; some antibiotics; and some antihypertensive drugs used to treat high blood pressure.
How common is inherited Long QT?
The frequency of Long QT is unknown but it appears to be a common cause of sudden and unexplained death in children and young adults. It is much more common than previously thought, possibly as frequent as 1 in 5,000, and may cause 3,000-4,000 sudden deaths in children and young adults each year in the United States. Estimations for Australia are more difficult to obtain.
The Jervell, Lange-Nielsen form is associated with congenital deafness and is rare, but the Romano-Ward variant, where the affected people have normal hearing, is being recognised with increasing frequency.
What are the symptoms of Long QT?
The usual symptoms are sudden loss of consciousness (syncope) or sudden death, typically occurring during physical activity or emotional upset. These most commonly begin in pre-teen to teen-age years, but may appear from a few days of age to middle age.
The syncopal episodes are often misdiagnosed as a common faint or a seizure. Actual seizures are uncommon in Long QT Syndrome. Sudden loss of consciousness during physical exertion or during emotional excitement should strongly raise the possibility of Long QT Syndrome. A family history of unexplained syncope or sudden death in young people should also raise suspicion.
About one third of individuals who have Long QT Syndrome never exhibit symptoms, and therefore the lack of symptoms does not exclude a person or family from having Long QT. Any young person who has an unexplained cardiac arrest should be considered for Long QT, as well as those with unexplained syncope (sudden loss of consciousness).
What causes the symptoms of Long QT?
People with Long QT Syndrome develop a very fast heart rhythm disturbance known as 'Torsades de pointes'. The rhythm is too fast for the heart to beat effectively, so the blood flow to the brain decreases, causing the sudden loss of consciousness. In most instances, there is no warning prior to losing consciousness.
Common triggers and consequences of the arrhythmias
Triggers include swimming; running; a suprise such as an alarm clock, a loud horn or ringing phone; anger; crying; a test; or other stressful situations. Sudden death may occur during sleep. Consequences include car accidents, apparent drowning, and dizziness or near fainting after exercise or sports.
How is Long QT Syndrome diagnosed?
Diagnosis of Long QT is commonly suspected or made from an ECG. It is often recommended that children and young adults should have an ECG as part of their evaluation for an unexplained loss of consciousness episode. Sometimes no testing, or only neurological testing with an electroencephalogram (EEG), is done. It may be necessary to request that an ECG be done and specifically evaluated for QT prolongation.
In about 10 per cent of LQTS patients, the QT interval on the initial ECG is normal, and in another 30 per cent the QT interval is only borderline prolonged; not prolonged enough to clearly make the diagnosis. In these cases, an exercise ECG will usually assist in clarifying the diagnosis.
The exercise test is preferably a low level, somewhat protracted, exercise test which allows the individual to exercise for 10 or more minutes without reaching a heart rate much in excess of 150-160 beats per minute. This prevents the T wave from merging with the P wave in normal subjects and simplifies the measurement of the QT interval. The principal abnormality to be identified is a prolonged QT interval relative to the heart rate, determined by an increase in the calculated QTc interval, and the appearance of bifidT-waves.
How is Long QT syndrome inherited?
Long QT is commonly inherited by autosomal-dominant transmission. This means that it affects boys and girls equally, and that each child of an affected parent has a 50 per cent chance of inheriting the gene. In a large family, approximately 50 per cent of the children would be predicted to inherit the gene. In usual-size families, it can range from all children to no children being affected, as each child has an independent 50/50 chance of inheriting the gene.
It is extremely important that all family members be tested for the syndrome once a family member is identified as a Long QT Syndrome patient. The testing should include the parents, all siblings, any children of the affected individual, and all relatives of the affected parent. It is extremely important that all patients be identified early in order to prevent the tragic and unnecessary sudden deaths that may occur.
Genetic information
Little is known about the Jervell, Lange-Nielsen form of Long QT. It is rare and there have been no reports yet on any genes for this form in the United States.
In the Romano-Ward form, 4 genes have been found, KVLQT1, on chromosome 11 (LQT1), HERG on chromosome 7 (LQT2), SCN5A on chromosome 3 (LQT3), and Min K on chromosome 21 (LQT5), which interact with KVLQT1 to produce long QT syndrome.
Another gene is known to be located on chromosome 4 (LQT4), but the gene has not yet been identified. It is thought that other genes exist in addition to these. The symptoms, signs and treatment of the disease vary somewhat depending on the gene involved.
In the United States, genetic testing will become available for diagnosis of Long QT Syndrome sometime in the future. It is available now on a limited basis in certain research laboratories, and it takes a number of months at the quickest to get back the results. Fortunately, in most cases the diagnosis can be made accurately in the absence of the genetic tests. When all the genes are identified, genetic testing should markedly improve the ability to make the correct diagnosis in those patients with atypical symptoms or borderline QT intervals.
How do you treat Long QT?
Beta blocker medications are the mainstay of therapy for many people with Long QT Syndrome. These medications are effective in about 90 per cent of affected people.
New information regarding the genetics of the syndrome suggests that a subset of patients might be treated with other drugs, either instead of or in addition to the beta blocker medications. This can be discussed with a physician and it depends upon the gene type that you have. In people who do not respond to medication, the insertion of a pacemaker, or automatic defibrillator, or the surgical cutting of certain nerves in the neck, called cervico-thoracic sympathectomy, can be utilised.
All people with symptoms should be treated, and because it is not possible to predict which people are vulnerable to syncope and sudden death, and sudden death often occurs with the first episode, asymptomatic patients (those displaying no symptoms), especially children, should also be treated.
Should activity be restricted?
Since the symptoms are often precipitated by physical exertion or emotional upset, it is appropriate to restrict physical activity in symptomatic individuals and it is seen as reasonable even in those without symptoms. For most individuals, this only requires refraining from competitive and vigorous sports. Recreational activities are often allowable.
The ‘buddy system’ is a wise strategy for Long QT patients. In individuals with continued symptoms, further restriction of activity may be necessary.
What about pregnancy and surgery?
Although labour and delivery and surgical procedures are stressful and physically exacting events, it is uncommon for Long QT Syndrome patients to experience symptoms during these times. It is important to be sure that the blood potassium is maintained. It may be reduced if diuretic medications are used or if there is sweating, vomiting or diarrhoea, and potassium supplementation may be necessary during these times.
Drugs to avoid
There are a number of drugs which are known to prolong the QT interval and may cause heart rhythm abnormalities, particularly in patients with Long QT Syndrome.
These include antiarrhythmic drugs, used to control heart rhythm; some anticancer drugs; some antidepressants; some migraine medications; some antipsychotic medications used to treat schizophrenia; some antibiotics; and some antihypertensive drugs used to treat high blood pressure.
You should always inquire of your physician or other health care provider about the risk of any medication suggested or prescribed for you. Always inform them of your Long QT Syndrome and make sure they know there are many medications which are contraindicated in this condition.
Last Reviewed: 26 April 2001
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