Davendra Mehta, MD, PhD
Director of Cardiac Electrophysiology
Mount Sinai St. Luke's
Professor of Medicine (Cardiology)
Icahn School of Medicine at Mount Sinai
Awareness of Long QT Syndrome Could Save Your Life
The heart is a remarkable organ, beating around 100,000 times a day to keep us alive. The time it takes from one heartbeat to the next is precisely calibrated to ensure the flow of oxygen-rich blood throughout our bodies. When this careful timing is interrupted, as happens with a rare disorder called long QT syndrome, tragedy can result.
According to the National Institutes of Health, about one in 7,000 people in the United States has long QT syndrome, but it often goes undiagnosed. While it causes about 3,000 to 4,000 sudden deaths in children and young adults each year, treatment is available, and there are steps individuals can take to minimize their risk.
What Is Long QT Syndrome?
Long QT syndrome (LQTS) is a disorder of the heart's electrical system. An electrical signal stimulates your heart to contract and push blood out to your body; before beginning the next contraction, your heart pauses to recover from the electrical action and refill with blood. The time this cycle takes is called the QT interval because it is visually represented on an electrocardiogram (EKG) by linear waves labeled Q through T. (An EKG is a test that records the electrical activity of the heart.)
A normal QT interval depends on proper functioning of the heart cells' sodium, calcium, and potassium ion channels, which are involved in contracting and relaxing the heart muscle. In people with LQTS, some channels malfunction, causing a prolonged QT interval. This can lead to heart rhythm problems (arrhythmias), such as a faster-than-normal heart rate; rapid, irregular heartbeats; and torsades de pointes, a potentially fatal type of arrhythmia specific to LQTS.
Long QT syndrome can cause temporary loss of consciousness and cardiac arrest, as well as sudden death -- which, unfortunately, is sometimes the first symptom of untreated LQTS.
What Causes Long QT Syndrome?
LQTS can be congenital (present at birth) or acquired (developed under certain conditions).
Congenital LQTS is related to an inherited genetic defect. Thirteen genes have been associated with the disorder, but mutations on three of them account for most cases. Because the gene abnormalities are present at birth, congenital LQTS often is diagnosed in childhood, sometimes as early as one or two years old. Risk of arrhythmia is related to a patient's particular gene defect. For instance, people with a mild genetic abnormality might not experience symptoms unless exposed to a trigger, such as an LQTS-inducing drug.
Congenital LQTS manifests in different ways, depending on the particular gene affected. In patients with long QT syndrome type 1 (LQTS1), arrhythmia is commonly triggered by exercise, especially swimming. Patients with LQTS2 may experience arrhythmia after being startled, such as by a loud telephone ring. For those with LQTS3, arrhythmia is usually triggered at night during sleep.
Acquired LQTS usually is caused by certain commonly prescribed medications that can lengthen the QT interval, triggering dangerous arrhythmias in some patients. Among several classes of drugs that can induce this disorder, those at highest risk include medications for cardiac arrhythmias; drugs used to treat psychiatric illness; and antibiotics, particularly those in the quinolone and macrolide families. An extensively used pain reliever called methadone, and some cold medications also may cause a prolonged QT interval. A complete list of these drugs is available at QTdrugs.org and other websites. If any medication you take is listed, your doctor can help determine and monitor your risk for acquired LQTS.
Acquired LQTS also can occur due to an electrolyte disturbance, such as low potassium caused by severe diarrhea or vomiting.
Who Should Get Evaluated for Long QT Syndrome?
In people with no symptoms, LQTS is often revealed on an EKG during a routine physical exam. Any child who faints should be checked for LQTS, and all individuals should be evaluated if they:
• Experience sudden loss of consciousness or cardiac arrest while exercising, upon startling, or during sleep;
• Have a family history of sudden death at a young age; or
• Have a relative with LQTS.
An EKG is the main diagnostic tool for LQTS. However, not everyone with LQTS will always exhibit a prolonged QT interval on an EKG, such as someone who has it during intense exercise but not at rest. In these situations, medications may be used to try and reproduce a prolonged QT interval that can be measured on EKG.
The Importance of Genetic Testing
When a person is diagnosed with long QT syndrome, genetic testing is recommended. If a genetic cause is found, it is important for other family members to get tested to see if they carry the same gene mutation.
Most people with congenital LQTS can be treated effectively with daily beta-blocker medication, which slows the heart rate and diminishes the risk of dangerous heart rhythms. Some people with mild LQTS may only need to take preventive measures.
Survivors of a long QT-related cardiac arrest or patients who continue to have symptoms despite beta-blocker therapy may need a surgically implanted cardioverter defibrillator, a small device similar to a pacemaker that helps control abnormal arrhythmias and prevent cardiac arrest and sudden death.
Acquired LQTS is treated by stopping the associated drug or correcting any electrolyte abnormality, depending on the cause.
In addition to treatment, it is critical for every patient diagnosed with LQTS to take precautions to prevent life-threatening heart rhythms. These include avoiding drugs known to induce LQTS, and quickly replenishing fluids and electrolytes in cases of severe diarrhea or vomiting. Depending on the type of LQTS one has, doctors may advise additional lifestyle changes, such as avoiding strenuous exercise or other triggers.
It is important to remember that even though there is no cure for LQTS, many deaths can be prevented through early diagnosis, proper precautions, and appropriate treatment.