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Long QT Syndrome
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The NHLBI developed the Diseases and Conditions Index (DCI) for patients and the public. The DCI contains plain-language health information about diseases, conditions, tests, and procedures related to the heart, lungs, blood, and sleep.
The Heart Rhythm Society is the international leader in science, education and advocacy for cardiac arrhythmia professionals and patients, and the primary information resource on heart rhythm disorders. Its mission is to improve the care of patients by promoting research, education and optimal health care policies and standards.
When a patients heart stops working properly, paramedics have to act fast to stabilize the patient, often using defibrillators and heart medication to restart the heart and mitigate the damage that can result from even brief cardiac arrest. These pages cover the basics and the in-depth research behind advanced cardiac life support.
The SADS Foundation is dedicated to informing the general public, families, and medical professionals about the effects of untreated/undiagnosed cardiac arrhythmias and the methods by which death can be prevented.
Sudden Cardiac Arrest Foundation is a non-profit organization dedicated to increasing the awareness of sudden cardiac arrest. Its mission is to "raise awareness and support programs that give 'ordinary' people the power to save a life."
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(Source: NIH / National Heart, Lung and Blood Institute) Long QT syndrome (LQTS) is a disorder of the heart's electrical activity. It can cause sudden, uncontrollable, dangerous arrhythmias (ah-RITH-me-ahs) in response to exercise or stress. Arrhythmias are problems with the rate or rhythm of the heartbeat. People who have LQTS also can have arrhythmias for no known reason. However, not everyone who has LQTS has dangerous heart rhythms. When they do occur, though, they can be fatal.

What Does "Long QT" Mean?

The term "long QT" refers to an abnormal pattern seen on an EKG (electrocardiogram). An EKG is a test that detects and records the heart's electrical activity.

With each heartbeat, an electrical signal spreads from the top of your heart to the bottom. As it travels, the signal causes the heart to contract and pump blood. An EKG records electrical signals as they move through your heart.

Data from the EKG are mapped on a graph so your doctor can study your heart's electrical activity. Each heartbeat is mapped as five distinct electrical waves: P, Q, R, S, and T.

The electrical activity that occurs between the Q and T waves is called the QT interval. This interval shows electrical activity in the heart's lower chambers, the ventricles (VEN-trih-kuls).

The timing of the heart's electrical activity is complex, and the body carefully controls it. Normally the QT interval is about a third of each heartbeat cycle. However, in people who have LQTS, the QT interval lasts longer than normal.

A long QT interval can upset the careful timing of the heartbeat and trigger dangerous heart rhythms.

Overview of Long QT Syndrome

On the surface of each heart muscle cell are tiny pores called ion channels. Ion channels open and close to let electrically charged sodium, calcium, and potassium atoms (ions) flow into and out of each cell. This generates the heart's electrical activity.

In people who have LQTS, the ion channels may not work well, or there may be too few of them. This may disrupt electrical activity in the heart's ventricles and cause dangerous arrhythmias.

LQTS often is inherited, which means you're born with the condition and have it your whole life. There are seven known types of inherited LQTS. The most common ones are LQTS 1, 2, and 3.

In LQTS 1, emotional stress or exercise (especially swimming) can trigger arrhythmias. In LQTS 2, extreme emotions, such as surprise, can trigger arrhythmias. In LQTS 3, a slow heart rate during sleep can trigger arrhythmias.

You also can acquire LQTS. This means you aren't born with the disorder, but you develop it during your lifetime. Some medicines and conditions can cause acquired LQTS. 

Outlook for Long QT Syndrome

More than half of the people who have untreated, inherited types of LQTS die within 10 years. However, lifestyle changes and medicines can help people who have LQTS prevent complications and live longer.

Some of these lifestyle changes and treatments include:

  • Avoiding strenuous physical activity or startling noises.
  • Adding more potassium to your diet (as your doctor advises).
  • Taking heart medicines called beta blockers. These medicines help prevent sudden cardiac arrest.
  • Having an implanted medical device, such as a pacemaker or implantable cardioverter defibrillator. These devices help control abnormal heart rhythms.

If you have LQTS, talk with your doctor about which lifestyle changes and treatments are best for you.

Source: NIH / National Heart, Lung and Blood Institute

Key Point 1

Long QT syndrome is an electrical problem in the heart. It can be associated with medications as well; it’s a bit more complicated as well, but it can lead to sudden cardiac arrest.  If you are, or may be, at risk you need to be monitored by a cardiologist.

Key Point 2

As frightening as long QT syndrome can be, it’s important to know there are long-term effective treatments.  The critical thing to know is that you might be at risk and then you’ve got to ask for help because otherwise you’re not going to get it.


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Conduct an off-site search for Long QT Syndrome from MedlinePlus.  These up-to-date search results are based on search terms specific to Second Opinion Key Points.

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