What is long QT syndrome?
The long QT syndrome (LQTS) is a heart condition in which there is an abnormally long delay between the electrical excitation (or depolarization) and relaxation (repolarization) of the ventricles of the heart. It is associated with syncope (loss of consciousness) and with sudden death due to ventricular arrhythmias. Arrhythmias in individuals with LQTS are often
associated with exercise or excitement. The cause of sudden cardiac death in individuals with LQTS is ventricular fibrillation.
Individuals with LQTS have a prolongation of the QT interval on the ECG. The Q point on the ECG corresponds to the beginning of ventricular depolarization while the T point corresponds to the beginning of ventricular repolarization. The QT interval is measured from the Q point to the end of the T wave. While many individuals with LQTS have persistent prolongation of the QT interval, some individuals do not always show the QT prolongation; in these individuals, the QT interval may prolong with the administration of certain medications.
The Long QT Syndrome is a rare disorder of the heart's electrical system that can affect otherwise healthy people. Although the heart's mechanical function is normal, there are defects in ion channels, which are cell structures in the heart muscle. These electrical defects can cause a very fast heart rhythm (arrhythmia) called torsade de pointes. This abnormal rhythm (a form of ventricular tachycardia) is too fast for the heart to beat effectively, and so the blood flow to the brain falls dramatically, causing sudden loss of consciousness, or syncope.
The name Long QT Syndrome comes from the measurement of the heart's contractions by electrocardiogram (EKG or ECG). When the heart contracts, it emits an electrical signal that can be recorded on the ECG. This signal produces a waveform, and different parts of this waveform are designated by letters - P,Q, R, S and T. The Q-T interval marks the time for electrical activation and inactivation of the ventricles, which are the lower chambers of the heart. In people with the Long QT Syndrome, the Q-T interval takes longer than normal to occur. It should be noted, however, that tests do not always reveal Long QT Syndrome. People with the disorder do not necessarily have a prolonged Q-T interval all the time, and at the time they have an ECG, the Q-T interval may be normal.