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Long QT Syndrome: Diagnosis, Causes and Treatment

Long QT Syndrome is an inherited disorder of the heart’s pumping mechanism that can result in an abnormal heart beat (arrhythmia). It can lead to a dangerous kind of arrhythmia in which the lower chambers (ventricles) beat so fast (ventricular tachycardia or ventricular fibrillation) that the heart cannot pump the blood it needs for the brain to work normally. Arrhythmia episodes can occur suddenly, leading to fainting, or sometimes to cardiac arrest and sudden death.

Unlike some inherited arrhythmias, where episodes occur during sleep, LQTS is more typically associated with arrhythmias (and death) that are triggered by exercise or being startled.

Although the average age of a patient with sudden cardiac death is 35 to 40 years old, patients with inherited arrhythmias may range from six months to 75 years old. In addition, inherited arrhythmias tend to occur more in males.

Long QT Syndrome Topics

How LQTS disrupts your heartbeat

Your heart’s four chambers—the two upper atria and two lower ventricles-- pump blood by contracting and relaxing in an even, rhythmic pattern. Your heartbeat is controlled by an electrical system that sends impulses through your heart muscle. The sinus node, located in the right atrium, conducts the impulses that start each heartbeat.

The pumping pattern works like this: The atria receives blood and squeezes it into the ventricles. When the atria relax, the ventricles contract, and pump blood to your lungs and out to the body. After each heartbeat, the heart must recharge and get ready for the next heartbeat.

When Long QT Syndrome occurs, there is a delay at the end of each heartbeat, and the heart takes longer than it should to recharge. This delay can be seen on the “Q through T” wave of an electrocardiogram (described below) which is how the syndrome gets its name

The abnormality that disrupts this phase of the heartbeat usually originates back to the electrical system’s inability to process potassium to the outside of heart cells, although there is one type of LQTS in which sodium is not properly processed.


In most cases, LQTS is inherited. This means that if one of your parents has the condition, you have a higher chance of having it. However, sometimes a parent who has the genetic variants associated with LQTS, may never have the condition. Also, sometimes there are new cases of abnormal genes (de novo mutations), that aren’t traced back to parents.

Many medications (certain heart rhythm drugs, antihistamines, antibiotics) can cause what’s known as an acquired form of LQTS. Acquired conditions are conditions that have an environmental, not genetic cause. However, scientists believe that even those who develop this acquired form of LQTS, are genetically predisposed to developing the condition and that a medication may have triggered it.

Signs and Symptoms

Arrhythmias that occur with LQTS typically occur when the affected person is exercising or is startled (possibly leading to sudden cardiac death). Some people do not experience signs or symptoms during an arrhythmia episode while others may experience any of the following:

  • pounding or fluttering in the chest
  • shortness of breath
  • seizure
  • fainting spells (syncope)

When LQTS is suspected—either for genetic reasons or when a person faints during physical exertion, a patient is typically referred to a doctor that specializes in heart disease (cardiologist) or a cardiologist that specializes in heart rhythms (electrophysiologist). A careful evaluation including a family health history and physical examination are performed.

As with other inherited arrhythmias, LQTS can be difficult to diagnose. Although it is usually detected on an electrocardiogram (ECG)—a test that measures electrical signals as they travel to the heart--sometimes the ECG findings are very subtle, which is why it is so important to see a specialist. Sometimes, certain medications are given to unmask the subtle changes that identify a person at risk for an arrhythmia. Other times additional tests may be performed.

During an ECG, electrodes are placed on the skin and electrical signals are measured and recorded in five distinct waves. The “P” wave measures signals from the heart’s atria, and waves Q through T show signals from the ventricles. The QT interval shows the length of time it takes ventricles to contract, and then refill before the next contraction. As mentioned, Long QT syndrome occurs when it takes too long to for the ventricles to contract. .

There are a number of conditions that may cause an LQTS pattern on an ECG, and because of the implications of the diagnosis, these conditions must be ruled out. If someone faints without an unidentifiable cause (particularly a younger person in which all other tests are normal) that person should be evaluated by a cardiac electrophysiologist using testing that is only available within this specialty.

If someone has a history of fainting and is found to have LQTS, the likelihood that this person will experience recurring episodes of fainting or sudden cardiac death is up to 40 percent during the next 2-3 years.

If you have LQTS, it is important that your siblings and children be screened for the condition.


To manage Long QT syndrome, doctors frequently recommend one of the following (alone or in combination):

  • Medication – Beta blockers, which work by blocking the effect that adrenaline has on the heart, are sometimes helpful in managing certain types of LQTS, but they may not always be effective.
  • Repeated ECGs – Repeated ECGs or 24-hour monitoring of heart rhythms are frequently performed to identify findings characteristic of LQTS.
  • Implantable cardioverter defibrillator (ICD) – This implantable device is tiny -- about the size of a small pager -- and getting smaller with each innovation. An ICD can detect and prevent the kind of arrhythmias responsible for causing patients to faint or die. If the ICD detects this type of arrhythmia, it sends energy to the heart to “shock” it back to a normal rhythm. When provided with an ICD, the rate of death in patients with LQTS syndrome has been 0 percent with up to 10 years follow-up.


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