Long QT syndrome (LQTS) PDF version
Long QT syndrome is a disease that affects the electrical activity of the heart. The QT interval is a measurement of part of the heartbeat seen on an electrocardiogram (ECG). The heartbeat is controlled by a complex electrical system, which when stimulated causes the heart muscle to contract. Once the muscle has contracted, it must have time to recover and relax before the next electrical signal is received. The length of time this relaxation takes is called the QT interval. In people with long QT syndrome this interval is longer than normal (as the name suggests). If the next signal arrives too early (i.e. when the muscle has not fully recovered from the last contraction) it can cause the heart to beat abnormally fast, leading to dizziness, black-outs or even death.
Long QT syndrome most often affects children and young adults. The most common symptom is fainting or collapses. These episodes are often associated with activities that increase the heart rate, such as exercise (particularly swimming), emotional situations and sudden loud noises. Diagnosing long QT syndrome can be difficult, as many people often do not display symptoms. Once diagnosed however, effective treatments are available.
Some medications can further prolong the QT interval or increase the risk of an abnormal fast heart rhythm. If you have suspected or confirmed long QT syndrome you should be familiar with the full list of drugs that you must avoid.
How it is inherited
The most common form of long QT syndrome is inherited as an autosomal dominant disease (see Genetic Inheritance and Testing for more information). One of the more rare forms of long QT syndrome is called Jervell Lange-Neilsen syndrome, which is inherited in an autosomal recessive manner and is also associated with deafness.
Genetic testing for long QT syndrome is commercially available. It involves testing six of the common genes known to cause the disease. The family alteration will be identified in about 70% of cases. Understanding more about the gene causing disease in your family can provide useful information to your cardiologist and may even alter your medical management.
If you would like to find out more about how genetic testing may be useful in your family, please contact your nearest Cardiac Genetic Service .
Your cardiologist will decide what medications or treatments you may require.
Beta-blockers is a medication commonly used in the general population to treat high blood pressure. They are used in LQTS patients to slow the heart rate and reduce the effect of sudden exertion or excitement on the heart. As beta-blockers make the heart beat slower, it allows blood to completely fill the chambers before it is pumped out, leading to improved heart function. Examples include Metoprolol, Atenolol, and Nadolol.
Implantable defibrillator: Your risk of sudden death is also something that your cardiologist will assess. If your cardiologist believes you may be at increased risk of dying suddenly, he/she will often advise an automatic implantable cardioverter-defibrillator (AICD). This is a device (similar to a pacemaker) that is inserted in to the chest, with leads extending down in to the heart. The AICD monitors the hearts rhythm and if it becomes abnormal (the type of heart rate that occurs during a cardiac arrest), it will deliver an electric shock to revert the heart back to a normal rhythm. Importantly, beta-blockers are also particularly effective in preventing sudden death in long QT syndrome. As your cardiologist determines your level of risk based on certain criteria, you should report any new symptoms or events to your cardiologist immediately, including black-outs or if a family member passes away unexpectedly.
Advice to family members
Direct relatives of someone who has been diagnosed with LQTS should have their hearts checked by a cardiologist, which is known as Clinical Screening. Direct family members include children, brothers and sisters, and parents. As LQTS is an inherited heart condition, these family members are generally at a 1 in 2 (50%) risk of also carrying the gene and are termed at-risk relatives.
We rely on this information being passed on within a family, and would therefore ask you to encourage any at-risk relatives to arrange an appointment with a cardiologist. We know there is huge variability in the range of symptoms seen even within a family (with some family members having minimal symptoms, while others have the most serious outcomes such as sudden death). So even while an at-risk relative may feel healthy and well, it is possible they could have mild disease. If this was deemed to be the case, treatment would not necessarily be initiated in this relative, but we would then know his/her children are now at-risk. Please talk to the coordinator of a Cardiac Genetic Service near you for more information or to organise a ‘heart check’.
Australian Genetic Heart Disease Registry
LQTS is one of the diseases being investigated by the Registry. We aim to enrol every family in Australia with LQTS. Find out more about the Registry or enrol yourself or your family by emailing the Registry Coordinator.