What is Long QT Syndrome?

Long QT syndrome (LQTS) is a disorder of the heart's electrical activity. It may cause you to develop a sudden, uncontrollable, and dangerous heart rhythm in response to exercise or stress.

Arrhythmias also can develop for no known reason in people who have LQTS. Not everyone who has LQTS develops dangerous heart rhythms. However, if one does occur, it may be fatal.

The term "long QT" refers to an abnormal pattern seen on an electrocardiogram (ECG or EKG). An ECG is a test that detects and records the heart's electrical activity. The QT interval, recorded on the ECG, corresponds to the time during which the ventricles lower chambers of your heart) are triggered to contract and then build the potential to contract again.

Illustration of Long QT Syndrome, heart rhythms

With each beat, the heart contracts and relaxes. If the heart takes longer than usual to contract and relax, there is a wider space between the Q and T. This could mean that the person has long QT syndrome.

The timing of the heartbeat's electrical activity is complex, and the body carefully controls it. Normally the QT interval of the heartbeat lasts about a third of each heartbeat cycle on the ECG.

However, in people who have LQTS, the QT interval usually lasts longer than normal. This can upset the careful timing of the heartbeat and trigger a dangerous, abnormal rhythm.

If you have inherited LQTS, you received the faulty gene(s) from one or both of your parents. Inherited LQTS is a lifelong condition.

Other names for Long QT Syndrome include the following:

  • Romano-Ward syndrome, affecting 1 in 5,000 people worldwide
  • Jervell and Lange-Nielsen syndrome affecting 1 in 6 million people worldwide, associated with deafness

NOTE: Jervell and Lange-Nielsen syndrome (J-LN) is the most severe variant of LQTS, with a very early onset and major QTc prolongation (the QT interval length corrected for changes in heart rate), and in which beta-blockers (drugs) have limited efficacy. Subgroups at a relatively lower risk for sudden cardiac arrest (CA/SD) are identifiable and include females, patients with a QTc  550 ms, those without events in the first year of life, and those with mutations on KCNE1. Early therapy with implanted cardioverter/ defibrillators must be considered.