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Long QT Syndrome

What is long QT syndrome?

Long QT syndrome (LQTS) is a disease that can cause a dangerous rapid heart rate and irregular rhythm involving the bottom pumping chambers of the heart (ventricles). The heart has both muscular and electrical components. Electricity flowing through the heart muscle triggers the muscle to squeeze (contract) or beat. Heart muscle cells use highly coordinated ion channels to keep the flow of electricity moving to generate normal heartbeats. Ion channels are what the electrolytes potassium, sodium, and calcium flow through within the heart's cells. In LQTS, a problem in the ion channels leads to an upset in the flow of electricity that causes a prolonged "repolarizing" of the heart cells. This can create a set-up for a very rapid and dangerous heart rhythm (arrhythmia). This can cause fainting or sudden death. The arrhythmias are called ventricular tachycardia or ventricular fibrillation. 

The name, long QT, stems from a reading on the electrocardiogram (ECG) machine. Healthcare providers use the ECG to evaluate your heartbeat and rhythm. The ECG machine records and measures each of your heartbeats as 5 “waves.” Each wave has a different letter designation: P, Q, R, S, and T. The relationship between the Q and T waves is important and is known as the QT interval. During this interval, the ventricles (lower chambers) are "repolarizing" or preparing for the next wave of electricity that will elicit a heartbeat. When the interval lasts longer than it normally should, it disrupts the timing of your heartbeat and can cause dangerous arrhythmias, or irregular heart rates.

What causes long QT syndrome?

Often, LQTS is passed down through families (genetic). Only one parent needs the genetic problem for it to be passed on to the child. If one of your family members is diagnosed with LQTS, experts advise that you and your other family members — parents, siblings, children — get tested as well. In rare instances, certain diseases or medicines can cause acquired LQTS. These diseases and/or medicines may affect the ion channels in the heart or cause electrolyte problems such as low potassium and calcium. More than 50 medicines list LQTS as a risk. Ask your healthcare provider about the risks of all medicines you're taking.

Who is at risk for long QT syndrome?

If you have a family history of LQTS, you are at risk of developing it. Specialists believe that if you are susceptible to long QT syndrome, you are more likely to be affected by medicines that increase your risk for the condition. Medicines such as antibiotics, antidepressants, antihistamines, diuretics, and heart medicines may increase your risk for LQTS.

What are the symptoms of long QT syndrome?

Some people with LQTS have no symptoms. The condition is detected on an ECG or heart monitor done for other reasons. If ventricular arrhythmias do occur as a result of LQTS, some symptoms include:

  • Chest fluttering (palpitations)

  • Shortness of breath or chest pain

  • Lightheadedness that comes and goes

  • Near fainting or fainting

  • Cardiac arrest

How is long QT syndrome diagnosed?

An ECG is the main way to detect LQTS. If your healthcare provider notes that the interval between the Q and T waves of your heartbeat is longer than it should be, you may have LQTS. The QT interval can vary from one visit to the next and can change with activity. You may be given a Holter monitor. This is a portable, wearable ECG recording device. You can wear the Holter monitor over several days to get readings during different activities. Another option is having an ECG during exercise (exercise stress testing). QT shortening is a normal response to exercise. Genetic testing is also available for inherited LQTS. It may help identify genetic defects associated with LQTS. It may also be used to screen first-degree relatives for the condition.

How is long QT syndrome treated?

For acquired LQTS, correcting any electrolyte problems or changing medicines may be all that is needed. There is no cure for inherited LQTS, but treatment helps prevent symptoms and lowers the risk for fainting or cardiac arrest. Your doctor may prescribe medicines called beta blockers to reduce arrhythmias. If you continue to have arrhythmias that keep coming back, or have had sudden cardiac arrest, you may need an implantable cardiac defibrillator (ICD). This device is implanted underneath the skin in the front of the chest wall. A wire connects the device to the heart. The ICD monitors your heart rhythm. If needed, it can deliver therapy such as ATP (anti tachycardia pacing) or 1 or more brief electrical shocks to the heart to reset the rhythm.

Surgery is another option for some people with inherited LQTS. It involves removing certain nerves in your chest that influence the heart rhythm.

What can I do to prevent long QT syndrome?

You can't prevent inherited LQTS but you can reduce your risk for things that can trigger arrhythmias and sudden death:

  • See your healthcare provider regularly.

  • Take your medicines as prescribed. Don't take medicines that prolong the QT.

  • Follow limits on certain activities such as strenuous exercise and driving.

  • Stay away from high-stress situations that may trigger LQTS.

  • Ask your healthcare provider if you need a potassium supplement.

  • Wear a medical alert bracelet.

When should I call my healthcare provider?

Seek medical attention right away if you:

  • Have recurrent fainting or near fainting despite treatment with medicine

  • Receive a shock by your ICD

Also see your healthcare provider for evaluation if you have a family history of unexplained sudden death at a young age or have a relative with known LQTS.

Key points about long QT syndrome

  • Long QT syndrome is a rare heart disorder that upsets the electrical activity of your heart.

  • This electrical disruption can cause an abnormal heartbeat and even sudden death.

  • Family history of long QT syndrome is the main risk factor for developing the condition.

  • Medicine or an implantable cardioverter defibrillator (ICD) can help manage the condition.

  • Long QT syndrome is potentially fatal and requires medical help.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

  • Know the reason for your visit and what you want to happen.

  • Before your visit, write down questions you want answered.

  • Bring someone with you to help you ask questions and remember what your provider tells you.

  • At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

  • Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.

  • Ask if your condition can be treated in other ways.

  • Know why a test or procedure is recommended and what the results could mean.

  • Know what to expect if you do not take the medicine or have the test or procedure.

  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.

  • Know how you can contact your provider if you have questions.

Online Medical Reviewer: Lu Cunningham
Online Medical Reviewer: Quinn Goeringer PA-C
Online Medical Reviewer: Steven Kang MD
Date Last Reviewed: 3/1/2019
© 2000-2019 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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