Long QT syndrome (LQTS)
Long QT syndrome (LQTS)
is a congenital disorder characterized
You can be born with a genetic predisposition for long QT syndrome. In addition, more than 50 medications, many of them common, as well as electrolyte abnormalities and various medical conditions, may cause the condition.
Treatment for long QT syndrome may involve limiting your physical activity, avoiding certain medications or taking medications to prevent the development of a chaotic heart rhythm. Some people with long QT syndrome also need an implantable cardioverter-defibrillator (ICD) to prevent against sudden death.
Signs and symptoms
Not all people with long QT syndrome experience symptoms. A third or more never develop signs and symptoms and may be aware of their condition only from results of an electrocardiogram (ECG) performed because they have a family history of long QT syndrome or for an unrelated reason.
For people who do experience signs and symptoms of long QT syndrome, the most common signs include:
The main symptom fainting spells often occurs during exercise or emotional excitement, such as when you're startled, angry or scared. A person with long QT syndrome may lose consciousness, for example, while playing basketball or after hearing a startling noise, such as an alarm clock going off or a phone ringing.
Signs and symptoms of inherited long QT syndrome may start in the first months of life, or as late as middle age. Most people who experience symptoms from long QT syndrome have their first symptom during their first three decades of life. About half have their first cardiac symptoms by the age of 12.
Rarely, signs and symptoms of long QT syndrome may occur during sleep or arousal from sleep. Some doctors believe that inherited long QT syndrome may explain some cases of sudden infant death syndrome (SIDS).
Your heart beats 100,000 times a day to circulate blood throughout your body. To pump blood, your heart's chambers must contract and relax in a coordinated manner. Contraction and relaxation are controlled by electrical impulses that travel through your heart muscle like electricity through wires.
Your heart consists of four chambers two upper chambers (atria) that receive blood and two lower chambers (ventricles) that pump blood. Within the upper-right chamber of your heart is a group of cells called the sinus node. The sinus node produces the electrical impulse that starts each heartbeat.
Your heart is composed of two upper and two lower chambers. The upper chambers, the right atrium and left atrium, receive incoming blood. The lower chambers, the more muscular right and left ...A prolonged QT interval refers to an abnormality seen on an electrocardiogram that reflects a disturbance in how your heart conducts electricity.
Each impulse first travels through your heart's atria. The atria contract, squeezing blood into the two ventricles below. The atria relax. The impulse then travels through your ventricles, and the ventricles contract, pumping blood out to your lungs and the rest of your body. The ventricles then relax. This pattern of alternating contraction and relaxation of your heart's upper and lower chambers makes up your heartbeat.
After each heartbeat, your heart's electrical system recharges itself in preparation for the next heartbeat. In long QT syndrome, however, your heart muscle takes longer than normal to recharge between beats. This electrical disturbance can be seen on an electrocardiogram (ECG). Another abbreviation for this test is EKG.
Prolonged QT interval
An ECG measures electrical impulses as five distinct waves. Doctors label these five waves using the letters P, Q, R, S and T. The P wave shows electrical activity in your heart's upper chambers. The other waves, Q through T, reflect electrical activity in your heart's lower chambers.
The interval between the start of the Q wave and the end of the T wave (QT interval) corresponds to the time it takes for your heart's ventricles to contract and then rest before beginning the next contraction. In other words, the QT interval refers to the length of time it takes cells in your heart's lower chambers to electrically recharge between beats.
Doctors can measure a QT interval and can tell whether it occurs in a normal amount of time. If it takes longer than normal, it's called a prolonged QT interval.
Long QT syndrome results from abnormalities in the heart's electrical recharging system. However, the heart's structure is normal. Abnormalities in your heart's electrical system may be inherited or acquired.
Inherited long QT syndrome
Progress has been made in recent years in understanding the genetics of inherited long QT syndrome. Before these genetic breakthroughs, doctors initially described two forms of inherited long QT syndrome:
Scientists are investigating a possible link between SIDS and long QT syndrome. Researchers suspect that a small percentage of babies with SIDS had a genetic defect or mutation for this syndrome.
Acquired long QT syndrome
Medications capable of prolonging the QT interval and upsetting heart rhythm include certain antibiotics, antidepressants, antihistamines, diuretics, heart medications, cholesterol-lowering drugs, diabetes medications, as well as some antifungal and antipsychotic drugs.
People who develop drug-induced long QT syndrome also may have some subtle genetic defects in their hearts, making them more susceptible to arrhythmias from taking drugs that can cause prolonged QT intervals.
Sometimes strokes or other neurologic disorders can cause acquired long QT syndrome.
People at risk of long QT syndrome include:
Long QT syndrome is rare and often goes undiagnosed or misdiagnosed as a seizure disorder, such as epilepsy. However, researchers believe that long QT syndrome may be responsible for some otherwise unexplained deaths in children and young adults. For example, an unexplained drowning of a young person may be the first clue to inherited long QT syndrome in a family.
People with low potassium, magnesium or calcium in their blood such as those with the eating disorder anorexia nervosa may be susceptible to prolonged QT intervals. Potassium, magnesium and calcium are all important minerals for the health of the heart's electrical system.
When to seek medical advice
Sudden loss of consciousness during physical exertion or emotional excitement or after use of a new medication is a reason to see your doctor.
Because long QT syndrome can occur in families, consider seeing your doctor to be tested for long QT syndrome if a close relative (your parent, sibling or child) receives a diagnosis of or dies of suspected long QT syndrome.
Screening and diagnosis
If your doctor suspects that you have long QT syndrome, you may need to undergo several evaluations using an electrocardiogram to confirm the diagnosis and gauge the severity of the problem. In addition, your medical history and a list of your medications are important in diagnosing long QT syndrome.
Most people with suspected long QT syndrome have a clearly prolonged QT interval on an ECG. However, some don't, making the condition more difficult to diagnose. Other testing may then be necessary.
You may be referred to a cardiologist a doctor who specializes in the study of the heart and its function or a long QT syndrome specialist for additional tests such as:
Prolonged QT intervals may never cause any problems. However, physical or emotional stress may "trip up" a heart susceptible to prolonged QT intervals and cause the heart's rhythm to spin out of control.
A prolonged QT interval may trigger a particular irregular heart rhythm (arrhythmia) called torsades de pointes, in which your heart's ventricles beat fast. When this arrhythmia occurs, less blood is pumped out from your heart. Less blood then reaches your brain, causing you to faint.
If torsades de pointes is short lasting lasting less than one minute your heart can correct itself and beat normally again seconds later, and you regain consciousness on your own. However, if torsades de pointes persists, it can lead to a life-threatening arrhythmia called ventricular fibrillation.
In ventricular fibrillation, the ventricles beat so fast that your heart quivers and ceases pumping blood. Unless your heart is shocked back into a normal rhythm by a device called a defibrillator, ventricular fibrillation can lead to brain damage and death.