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 sets off 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. This causes a prolonged "repolarizing" of the heart cells. This delay means the heart isn't ready for the next beat. This can create a set-up for a very rapid and dangerous heart rhythm (arrhythmia) that may cause fainting or sudden death. These arrhythmias are called ventricular tachycardia, ventricular fibrillation, or Torsades de pointes.

The name, long QT, comes 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 five "waves." Each wave has a different letter designation: P, Q, R, S, and T. The relationship between the Q and T waves is important. It is known as the QT interval. During this interval, the lower chambers (ventricles) are "repolarizing" or preparing for the next wave of electricity that will call forth 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). But it's also possible to develop LQTS from disease or medicine (acquired). Only one parent needs the genetic problem for it to be passed on to the child. Experts advise that you and your other family members—parents, siblings, children—get tested as well if one of your family members is diagnosed with LQTS. In rare cases, certain diseases or medicines can cause acquired LQTS. These diseases or medicines may affect the ion channels in the heart or cause electrolyte problems. These include 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?

You're at risk for developing LQTS if you have a family history of it. Specialists believe that if you're susceptible to long QT syndrome, you're 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 found on an ECG or heart monitor done for other reasons. If ventricular arrhythmias do occur as a result of LQTS, some symptoms may 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 find 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 choice 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 linked to 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's needed. There is no cure for inherited LQTS. But treatment helps prevent symptoms and lowers the risk for fainting or cardiac arrest. Your healthcare provider 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 under the skin in the front of the chest wall or on the left side of your chest below the armpit.. A wire connects the device to the heart. The ICD keeps track of your heart rhythm. If needed, it can deliver therapy, such as ATP (anti-tachycardia pacing). Or one or more brief electrical shocks to the heart to reset the rhythm.

Surgery is another choice for some people with inherited LQTS. During surgery, certain nerves in your chest that influence the heart rhythm are removed.

What can I do to prevent long QT syndrome?

You can't prevent inherited LQTS. But you can do things to reduce your risk for things that can set off 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 set off LQTS.

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

  • Wear a medical alert bracelet.

When should I call my healthcare provider?

Get medical care 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 needs 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 healthcare provider if you have questions, especially after office hours or on weekends and holidays.

Online Medical Reviewer: Callie Tayrien RN MSN
Online Medical Reviewer: Stacey Wojcik MBA BSN RN
Online Medical Reviewer: Steven Kang MD
Date Last Reviewed: 9/1/2023
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