Some people with long QT syndrome don't have any symptoms. They may only become aware of their condition after having an electrocardiogram (ECG) for another reason.
Those who do have symptoms usually experience:
These symptoms can start unexpectedly and may be triggered by:
The heart usually returns to its normal rhythm after it's been beating abnormally.
But if it continues to beat abnormally and isn't treated in time with a defibrillator, the heart won't pump and the person will die. This is called cardiac arrest, and the heart rarely returns to normal if it isn't electrically corrected with shock.
Dial 999 to ask for an ambulance if someone with long QT syndrome suddenly collapses and doesn't regain consciousness. If you're able to, perform cardiopulmonary resuscitation (CPR) until medical help arrives.
Long QT syndrome is a leading cause of sudden cardiac death in young, otherwise healthy, people. It can also be an underlying cause of sudden infant death syndrome (SIDS).
Long QT syndrome is usually caused by a faulty gene inherited from a parent.
The abnormal gene affects the proteins that make up the ion channels regulating electricity in the heart. The ion channels may not work well, or there may not be enough of them, which disrupts the heart's electrical activity.
Certain medicines can also trigger long QT syndrome, including some types of:
But drug-induced long QT syndrome tends to only affect people who already have a tendency to develop the condition.
Cardiac Risk in the Young has published a list of medications that people with long QT syndrome should avoid.
The Sudden Arrhythmia Death Syndromes (SADS) Foundation has also produced a guide about acquired, drug-induced long QT syndrome (PDF, 158kb).
If your GP thinks you have long QT syndrome, if you have blackouts during exercise, or if you have a family history of unexpected and unexplained sudden death, they may recommend you have an ECG and refer you to a heart specialist (cardiologist).
An ECG records your heart's rhythm and electrical activity. If you have long QT syndrome, the trace of the QT section (showing part of the heartbeat) will be longer than normal. Sometimes an exercise ECG will be needed to confirm the diagnosis.
Genetic testing may be needed to identify the defective gene causing long QT syndrome. It can also help identify other family members who may have inherited the defective gene and need clinical assessment.
Most people with inherited long QT syndrome will need treatment with medicines. Beta-blockers, such as propranolol or nadolol, may be prescribed to help control irregular heartbeats and slow down your heart rate.
In some cases of long QT syndrome, surgery may be needed to control the flow of chemicals into the heart. This is known as a sympathectomy.
If medication is causing long QT syndrome, your medication will be reviewed and an alternative may be prescribed.
With the right treatment, it should be possible to lead a relatively normal life. However, you may need to make some lifestyle adjustments to reduce your risk of having blackouts.
For example, you may not be able to exercise strenuously or play competitive sports, and may need to try to avoid startling noises, such as alarm clocks. Avoiding stressful situations may also be recommended.
Rehydrating properly after a tummy upset is also essential, usually with supplements containing salt and sugar.
Your doctor may prescribe potassium supplements or suggest increasing the amount of potassium-rich foods in your diet. Good sources of potassium include:
Always tell medical staff that you have long QT syndrome. Any new medication, whether prescription or over the counter, will need to be carefully checked to see if it's suitable for you.
The British Heart Foundation has produced a booklet called Life with Inherited Abnormal Heart Rhythms, which has more information and advice about living with long QT syndrome and other inherited heart conditions.