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Long QT Syndrome Symptoms Causes Treatment

Long QT syndrome (LQTS) is a disorder of the heart's electrical activity that may cause you to develop a sudden, uncontrollable, and dangerous heart rhythm (called an arrhythmia) in response to exercise or stress. Such abnormal heart rhythms also can develop for no known reason in people who have LQTS. Not everyone who has LQTS develops a dangerous heart rhythm, but if one does occur, it may be fatal.

Long QT

Schematic representation of normal EKG trace (sinus rhythm), with waves, segments, and intervals labeled. Credit: Wikipedia.

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

The timing of the electrical activity of the heartbeat is complex and carefully controlled by the body. Normally the QT interval of the heartbeat lasts about a third of each heartbeat cycle on the EKG. But in people with LQTS, the QT interval usually lasts longer than normal, which can upset the careful timing of the heartbeat and trigger a dangerous, irregular rhythm.

Many cases of LQTS are inherited, which means you are born with the mutations of one or more genes that regulate heartbeats. There are at least nine types of inherited LQTS. The most common ones are called LQT-1, LQT-2, and LQT-3.

More than half the people who have an untreated, inherited form of LQTS die within 10 years. But for many people with LQTS, lifestyle changes and medical treatments can help prevent dangerous complications and lengthen life expectancy. Some of these changes include:

  • Avoiding strenuous physical activity or startling noises
  • Adding more potassium to your diet
  • Taking heart medicines called beta blockers, which are very effective at preventing sudden cardiac arrest
  • Having an implantable device, such as a pacemaker or implantable cardioverter defibrillator, that helps control abnormal heart rhythms