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Long QT Syndrome

What is Long QT Syndrome?

Long QT Syndrome is a disorder affecting the electrical activation the heart. This condition may cause abnormal heart rhythms which can cause fainting or, rarely, death. The condition is called Long QT syndrome because of an abnormality found on the electrocardiogram (ECG) – the interval between the Q wave and the T wave of the ECG is prolonged.

What are the Symptoms of Long QT Syndrome?

Some patients with Long QT Syndrome have no symptoms. Others have heart rhythm disturbances leading to fainting. If the heart rhythm disturbance persists, it may result in cardiac arrest or death. Occasionally, patients with Long QT Syndrome are misdiagnosed as having epilepsy, because the faints or blackouts may be accompanied by jerking of the limbs which gives the appearance of epilepsy.

How is Long QT Syndrome Diagnosed?

Long QT Syndrome is diagnosed on an electrocardiogram (ECG). The changes on the ECG may be present persistently or may come and go so that sometimes the ECG is normal. In some patients, an exercise stress test and/or adrenaline test in hospital is performed to “unmask” the long QT syndrome. Patients who have a family history of the condition may be diagnosed with genetic testing of a blood sample.

Family Screening and Genetic Testing

Long QT Syndrome is caused by a problem with a person’s genes. This condition is usually inherited in a pattern known as “autosomal dominant.”

Autosomal dominant conditions are important in families, as there may be more than 1 affected person in each family. All first-degree relatives (parents, siblings and children) of patients with Long QT Syndrome should be checked for the condition. Children of affected parents have a 1 in 2, or 50% chance, of Genetic testing involves a blood test. Currently, genetic testing is able to identify the cause of Long QT in approximately 70-80% patients. A positive genetic test result may affect management decisions in an affected individual.

It can also be used in at-risk family members to diagnose the condition in conjunction with clinical screening. Treatment and Lifestyle Modifications There is currently no treatment to “cure” the disease. Medications known as beta-blockers are used in most patients as they have been shown to reduce the risk of fainting episodes and cardiac arrest due. Some patients who have a higher risk of a cardiac arrest will have a defibrillator implanted.

Intense competitive sport should be avoided, as well as diving into swimming pools, as these activities may trigger abnormal heart rhythms. Patients with Long QT Syndrome should also avoid certain medications that prolong the QT interval. A list of these medications is available on It is advisable to notify your pharmacist of your condition before taking any prescribed or over the counter medication.

What is the Outlook For People with Long QT Syndrome?

The vast majority of those with Long QT Syndrome will lead normal and productive lives with a good quality of life. The risk of death is very low in those receiving appropriate treatment.

© Drs Caroline Medi and Mark McGuire Version 1.1 28/6/15

More info: NIH Long QT Syndrome