Long QT Syndrome

In a properly functioning cardiovascular system, certain proteins control the flow of potassium, sodium, magnesium, and other molecules through the heart’s cells. These molecules contribute to proper electrical activity in the heart and keep it beating in a steady pattern.

The QT interval is a way to measure the heart’s electrical recovery after each beat. Any problems—including genetic mutations to these proteins or medications that lengthen the QT interval—can disrupt this electrical activity and cause heart arrhythmia.

In Long QT Syndrome (LQTS), the heart takes longer to recover from each beat because its electrical activity is disrupted. If undiagnosed and untreated, LQTS can lead to fainting spells or torsades de pointes, a type of heart rhythm disturbance that causes sudden cardiac death.


  • Inherited LQTS occurs in approximately 1 in 2,000 people.
    Medical experts have identified mutations in 13 different genes that cause LQTS. Each type of inherited LQTS has certain triggers that may be associated with arrhythmias. The most common types are:
    • LQTS 1: Exercise (especially swimming) or emotional stress
    • LQTS 2: Extreme emotions including fright, anger, pain, or surprise
    • LQTS 3: Arrhythmias triggered by a slow heart rate while asleep
  • Acquired LQTS is much less common and does not often cause serious arrhythmias, except in people with a genetic predisposition.


For some people, their first symptom is a sudden cardiac arrest. Others have symptoms that begin in childhood or early teens, including:

  • Fainting caused by torsades de pointes, especially during physical activity or emotional stress
  • Sudden, rapid heart arrhythmia that feels like fluttering in your chest       
  • Gasping or difficulty breathing during sleep
  • Accidents caused by fainting

Diagnosis and Treatment

If you have symptoms of LQTS, physicians can diagnose it with an ECG. But, it can be difficult to diagnose because the QT interval may not always be prolonged in affected people.

Testing tools that can detect LQTS include:

  • Standard electrocardiogram (ECG) to check for a prolonged QT interval in your heartbeat
  • Event monitor to record your heart’s electrical activity over days or weeks to detect heart arrhythmia
  • Genetic testing to look for the condition

Your physician may also diagnose LQTS after you have experienced a cardiac event. A family history of sudden death may signal the need for further evaluation.  If you or a family member are diagnosed with LQTS, it’s very important for other family members to be screened for the syndrome. Contact MedStar Health for more information on genetic screening for heart conditions.

Treatment goals for LQTS focus on preventing heart arrhythmia and sudden cardiac arrest. Our cardiac specialists may recommend any of these treatment options:

  • Lifestyle changes
    • Avoiding strenuous activity, especially swimming
    • Avoiding medications that can trigger heart arrhythmia
    • Controlling stressful situations
  • Medications such as beta blockers to help regulate heart arrhythmia
  • Surgery to implant a defibrillator that uses electric shocks to correct heart arrhythmia
