What is Long QT syndrome?

By Dr Ananya Mandal, MD

Long QT syndrome (LQTS) is a disease that affects the normal heart rhythm and electrical activity. It may lead to sudden onset and dangerous arrhythmias (irregularities of heart rate and rhythm) which may be brought on by triggers like exercise or stress.

Arrythmias in people with LQTS may occur with no known cause. Not all patients with LQTS may have arrhythmias but in many cases such sudden arrhythmias may bring upon life threatening conditions and may be fatal.

The syndrome, which affects about one in 10,000 people, is usually diagnosed by examining a person's electrocardiogram (ECG or EKG). (1-5)

Diagnosis of long QT syndrome

An EKG or ECG (Electrocardiogram) is often performed to test the electrical activity of the heart.

Each heart beat entails generation of an electrical signal that spreads from the top of the heart to the bottom. This signal on its way makes the heart muscles contract and pump blood.

An EKG records electrical signals as they move through the heart muscles. With the use of probes or tabs placed over the skin of the chest these electrical activities are detected by the EKG machine and recorded by a writing stylus on a graph for the doctor to interpret the data.

Physiology of the heart

The electrical activity of the heart further depends on movement of ions. The surface of each heart muscle cell contains tiny pores called ion channels. These are gates that open and close to let electrically charged sodium, calcium, and potassium atoms to and fro from within to without the cell. This generates the heart's electrical activity.

Each heartbeat is mapped as five distinct electrical waves: P, Q, R, S, and T. The waves or peaks are marked out on a graph and the electrical activity that occurs between the Q and T waves is called the QT interval.

The QT interval shows electrical activity in the heart's lower chambers, the ventricles. It is contraction of the ventricles that leads to pumping out of the blood into the body’s circulation. The exact duration of this ventricular contraction is tightly regulated by the heart.

Normally the QT interval is about a third of each heartbeat cycle. In people with LQTS, the QT interval lasts longer than normal. This upsets the careful timing of the heartbeat and may trigger arrhythmias. Those with LQTS may have problems with their ion channels which may be too many or too few.

Cause of long QT syndrome

The exact cause of LQTS is unknown but the condition is inherited. There are seven known types of inherited LQTS.

Patients are born with the condition passed on to them from either or both of their parents and may suffer from it all their lives.

Some medicines and conditions can cause acquired LQTS. The most common ones are LQTS 1, 2, and 3.

In LQTS 1, emotional stress or exercise (especially swimming) can trigger arrhythmias. I

n LQTS 2, extreme emotions, such as surprise, can trigger arrhythmias whereas in LQTS 3, a slow heart rate during sleep can trigger arrhythmias.

Since the duration when the ventricle is refilling is prolonged, no blood is pumped out from the heart. The brain thus may become quickly deprived of oxygen leading to sudden loss of consciousness (syncope) and in some cases sudden death.

Symptoms of long QT syndrome

Symptoms typically begin in pre-teen to teenage years but may be seen in children as well. Typical symptoms include fainting spells during exercise or as a response to fear or surprise.

Fainting may also occur during sleep or arousal from sleep. The fainting spells are often sudden with no warning or dizziness.

Up to 50% of people with Long QT Syndrome never have any symptoms. These patients may remain undiagnosed till they have their sudden fainting spell that may lead to sudden cardiac death.

Treatment of long QT syndrome

Untreated genetically inherited LQTS may lead to death within 10 years. However, those that are detected and treated early along with lifestyle changes may survive longer.

Important lifestyle changes include avoiding strain, severe physical exercise, loud and sudden noises, adding potassium in diet, taking medications like beta blockers or getting a pace maker implanted to control the abnormal heart rhythms and rates.

Reviewed by , BA Hons (Cantab)

Further Reading

Last Updated: Oct 8, 2014

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