Long QT syndrome
Also known as: Jervell-Lange-Nielson syndrome; Romano-Ward syndrome
Long QT syndrome is a rare congenital condition. An affected child or person may not realise there is anything wrong until they suddenly develop a rapid heart rhythm. This very fast heart rhythm is called Torsades de Pointes, because of its appearance on an ECG (electrocardiogram) and is a type of ventricular tachycardia.
Medical text written January 2000 by Dr Jan Till. Last updated September 2013 by Dr Jan Till, Consultant Electrophysiologist and Lead for Inherited Cardiac Disease, Royal Brompton and Harefields Hospitals, London, UK.
The abnormal rhythm can happen at any age and is so fast that the heart cannot pump out blood as well as it should. As a result, the person suddenly faints or passes out during an attack. There may be little or no warning and these episodes are characteristically caused by sudden exercise, fear or noise. Sometimes the heart spontaneously recovers back to a normal rhythm, but not always, and therefore attacks are potentially life threatening.
Because of its rarity, and because the patient may appear to fit if the loss of blood supply to their brain lasts for sufficient length of time, attacks may be mistaken for the much more common condition of epilepsy.
The electrical instability of the heart arises from abnormal ion (K+/Na+) movement through channels in the cell membrane. These defective channels are coded for by mutations within genes. More than 13 different types have been discovered, each causing slightly different problems for the affected individual patient. These genetic faults (mutations) may arise for the first time in an individual during development or be inherited from one or both of their parents. Family screening is advised, in order to detect and advise anyone who may not know they are at potential risk.
The condition can be diagnosed by recording an ECG that shows a characteristic prolongation of an interval between the onset of excitation and the finish of recovery of the heartbeat; this is known as the QT interval. The exact QT interval is sometimes difficult to measure. In some people with the condition, the QT interval is greatly prolonged and is easy to recognise. In others it can be borderline prolonged and there is uncertainty. In this situation other helpful tests are an exercise test or a 24 hour recording.
Most affected people respond extremely well to beta blocking drugs. For those patients who do not respond well enough or who prove intolerant of beta blockers, a defibrillator can be considered. These devices help to regulate the heart rhythm, and will immediately discharge a small shock to restore the heart to normal in the event of an episode of ventricular tachycardia.
If inherited, long QT syndrome usually arises in an autosomal dominant fashion from one of the parents. Some people can inherit two mutations, and as a result are more likely to have more symptoms.
There is a special type of long QT where an individual has inherited two mutations, and these types of mutation code not only for deficient channels in the heart but also in the inner ear. These individuals are at higher risk from their long QT and are deaf.
In those families where the genetic abnormality has been identified, it may be possible to do prenatal genetic tests for that specific mutation.