Long QT Syndrome
The Inherited Arrhythmia Clinic in Madison, Wisconsin, was established to meet the needs of individuals and families with possible inherited arrhythmia syndromes, including Long QT Syndrome (LQTS), the most common form of inherited arrhythmia.
About Long QT Syndrome
The heart serves as a pump within our bodies that is stimulated by electrical signals to beat many times each minute, and is made up of millions of cells that discharge and recharge their electricity with each heartbeat. Long QT syndrome is caused by an abnormality in the heart's electrical system such that the heart takes longer than normal to recover from each heartbeat.
There are two ways that an individual can develop Long QT syndrome:
- Medication that interferes with the normal function of the heart's ion channels (proteins that control the passage of important chemicals such as potassium, calcium and sodium)
- A genetic mutation that causes a malformation of the heart's ion channels
The genetic form of Long QT syndrome is fairly rare, occurring in about one in every 3,000 people. Either way, this condition can predispose a person to a very dangerous arrhythmia (abnormal heart rhythm) known as torsades de pointes. This arrhythmia causes the heart to beat quickly and irregularly, preventing adequate blood flow to the brain and the rest of the body.
Diagnosing Long QT Syndrome
People with Long QT syndrome have structurally normal hearts and will generally appear to be in good health. The symptoms of Long QT syndrome can range from dizzy spells and fainting episodes to sudden cardiac death. Some people will more frequently experience these symptoms during exercise or exertion, times of emotional stress, or when they hear unexpected, loud noises. Most often, a person will have no warning that they are going to faint. Long QT syndrome will frequently present during childhood to the early twenties but can also be seen in people of all ages.
In making the diagnosis of Long QT syndrome, our clinic staff takes into account:
- QT interval prolongation and other ECG (a test to measure the electrical signal of the heart beat) findings
- Holter monitor results
- Family history
- Results of genetic testing
Treating Long QT Syndrome
Although there is currently no cure for Long QT syndrome, we do have treatment for it. Medications called beta blockers can significantly help and reduce risk of syncope and sudden death. However, other patients may need more medical intervention, such as the implantation of an implantable cardioverter defibrillator, which is essentially a pacemaker that can also shock the heart in the event of a dangerous arrhythmia. We also make recommendations for a person's lifestyle, such as eliminating or avoiding activities that could trigger a dangerous heart rhythm.
Long QT Syndrome and Genetics
The majority of genes associated with Long QT syndrome are important for the proper formation of the ion channels in the heart. Genetic testing is available to determine if a mutation, or gene change, can be found in any one of these genes.
There are several different types of Long QT syndrome and each type is associated with its own gene. The three most common types of Long QT syndrome are designated types 1, 2 and 3. We are typically able to identify a gene mutation in about 75 percent of patients that have symptoms of Long QT syndrome. This means there are some patients who have genetic mutations that cannot be identified at present. In the event that a mutation is not detectable in a patient with Long QT syndrome, we will make recommendations for screening family members who may also be at risk.
If a person does have a genetic mutation identified, we can test other family members to determine if they share this same genetic mutation. Relatives of a patient with an identified mutation have a 50 percent chance of sharing the same gene abnormality. The presence of a genetic mutation does not automatically indicate that a family member will also have symptoms or will develop symptoms of Long QT syndrome in the future. It does, however, let us know who should be evaluated by a cardiologist and which family members do not need a cardiac evaluation for Long QT syndrome.
Long QT Syndrome and Medication
All patients with Long QT syndrome should avoid any medication that is known to prolong the QT interval. A list of these drugs is available at QTDRUGS.org. It is important to check this website any time a new medication is prescribed.