Long QT Syndrome (LQTS) is an electrical disorder of the heart that may cause an erratic and fast heart beat (called an arrhythmia). This may result in fainting (also called 'syncope'), and in rare cases, cardiac arrest.

The QT Interval

The QT interval is measured on the electrocardiogram (ECG). It represents the time from the beginning of the heart's contraction to the end of its relaxation.

The QT interval may be prolonged due to a genetic abnormality or as the result of medication, electrolyte abnormalities (such as low potassium), or other illness.

The diagnosis of long QT syndrome is made when a prolonged QT interval on the ECG is accompanied by typical symptoms, or a family history of long QT, or in the presence of a genetic abnormality.

Genetic Forms of Long QT

When due to a genetic abnormality, there are three common forms:

1. Long QT Type 1 (gene: KCNQ1) - 30% of cases

2. Long QT Type 2 (gene: KCNH2) - 30% of cases

3. Long QT Type 3 (gene: SCN5A) - 10% of cases

Each form of Long QT has a unique clinical expression - with increased risk at different times of life and with certain activity.

Treatment

There are three pillars of treatment for Long QT Syndrome:

1. Lifestyle modification - each form of long QT carries its own risk. For example, swimming is a high risk activity in long QT type 1; loud noises may sometimes put the heart out of rhythm in long QT type 2. The specific advice for each form is detailed on their information page.

2. Avoidance of QT prolonging drugs - there are many drugs which may worsen QT prolongation and provoke arrhythmia. These may include some common antibiotic and psychiatric medications. A full list may be found on the "Credible Meds" website

3. Beta blockers- this class of medication protects against life-threatening arrhythmia. The most commonly prescribed beta blocker is called nadolol and is given once per day.

Uncommonly, a procedure called 'left cardiac sympathetic dennervation' or an implantable defibrillator may be recommended. These therapy are reserved for situations where medication is ineffective, not tolerated, or else the risk of serious arrhythmia is judged to be high.