Long QT syndrome is a group of congenital genetic conditions that create the possibility that the normal contraction of the ventricles of the heart will be irregular or absent altogether. On an EKG, this shows up as an unusually long interval in a normal sinus rhythm betweent the time the electrical signal passes into the ventricles (the Q wave) and the final contraction of the heart before it rests (the T wave). The condition can be set off by a number of different stimuli depending on the type of defect. Ironically, many of the drugs used to treat arrythmia can trigger the syndrome, as can some anti-psychotics. Long QT is very dangerous as it is not uncommon for a patient's heart to stop beating spontaneously due to the condition.
Diagnosis of the condition is very difficult. A long QT interval alone can occur in a person with a perfectly healthy heart, and many patients with Long QT have a normal interval much of the time. In order to confirm, there must also be episodes of tachycardia, fainting or palpitations. The same genes that cause Long QT can also cause deafness, so this can also help form a diagnosis. Finally, a family history of Long QT, or a sudden unexplained death from heart failure in the family, also strongly indicates Long QT.
The reason why a solid diagnosis must be reached is that Long QT is dangerous and difficult to treat. Medication can be given that makes it less likely that stress will trigger an arrythmia. However, if a patient has a history of previous heart attacks, a portable ventricular defibrillator is usually installed.