Long QT Syndrome

Frequently asked questions

What is the normal heart rhythm?
It is called "sinus" rhythm, because the electrical signal to contract originates in the sinus (or sinoatrial) node, the heart's natural pacemaker.  It then spreads through the heart's four pumping chambers, first through the two atria (right and left), then through the atrioventricular node and into the two main pumping chambers (right and left ventricles).

What is the QT interval?
It is a measurement made from the electrocardiogram (ECG or EKG). It reflects the duration of the electrical activity that stimulates contraction of the cells of the heart muscle. The QT interval is measured in milliseconds (msec) and it the time from the earliest contraction of the ventricles to the end of the repolarization wave, i.e. the Q wave. 

What is the corrected QT interval (QTc)?
The QT interval varies with the heart rate; it gets longer when the heart rate slows and it shortens when the heart beats faster. Therefore, in order to measure and interpret the QT interval, the measured value is "corrected" through the use of a mathematical formula to what it would be if the heart rate was at a strandard rate of 60 beats per minute. This correction formula is usually programmed into the machine that measures your ECG and the corrected QT interval (QTc) value is part of the information printed on the ECG. For men the QTc is normally less than 420 msec and for women the QTc is normally less than 440 msec. QTc values higher than normal are associated with increased risk of serious heart rhythm abnormalities (e.g. torsades de pointes).

What is long QT syndrome?
Long QT syndrome refers to a condition in which there is an abnormally long QTc interval on the electrocardiogram. It can be inherited ("congenital long QT") or induced by any of a large number of drugs or abnormal levels of the salts normally found in the blood, such as low potassium or magnesium ("acquired long QT"). The inherited form occurs due to the inheritance of abnormalities in certain proteins in the heart cells, and these protein abnormalities are in turn caused by abnormalities in the genes that produce those proteins.  A list of drugs that prolong the QT interval or cause torsades de pointes can be found on this website at View the QT Drugs List.

How do I know if I have long QT syndrome?
Measurement of the QT interval on the ECG is still the main method of determining whether someone has long QT syndrome. The diagnosis of long QT syndrome is complex and requires special training and expertise in cardiac electrophysiology.  At least 213 drugs are known to prolong the QTc and over a dozen different genetic abnormalities can cause the syndrome. Testing for these genetic abnormalities is not yet routine but can be performed, especially for people who have relatives who are known to have congenital long QT syndrome. 

What is torsades de pointes?
It is a cardiac arrhythmia, or heart rhythm abnormality, which may cause loss of consciousness or even sudden death. The phrase "torsades de pointes" is French and literally means "twisting of the points", referring to the characteristic appearance of the electrocardiogram during the abnormal rhythm. Torsades de pointes occurs when the QT interval on the electrocardiogram is excessively prolonged.

I sometimes have palpitations - what does this mean?
Palpitations are sensations of one's own heart beating in the chest. They may or may not be a symptom of a heart rhythm abnormality or other health problem. Your description of your palpitations (e.g. single beats or pauses, flutters, pounding, fast, slow, regular, irregular), how long they last and when they occur can give your doctor clues about what arrhythmia or other condition is causing them.

What other types of arrhythmia are there?
There are many types of heart rhythm abnormalities, also known as arrhythmias or dysrhythmias. If the rhythm is abnormally fast, it is called a tachycardia; abnormally slow rhythms are called bradycardias. Some rhythm abnormalities have a normal average heart rate (also called pulse rate), but are abnormal in that the rhythm is irregular or because some or all beats start in parts of the heart other than the sinus node, the heart's normal pacemaker.

What is syncope?
Syncope is essentially a "fainting" spell. It is what happens when there is not enough blood flow to the brain. A person can pass out, or feel very lightheaded and fall down or slump over. Conditions such as hot weather, stuffy rooms, warm baths, prolonged standing or suddenly standing up, pain, dehydration, and anemia, may cause syncope.

I fainted recently - what should I do?
You should discuss it with your doctor. Tell the doctor exactly what happened, and what medications (including non-prescription medicines and herbal or dietary supplements) you've been taking, especially any new or temporary ones. The doctor will decide whether it may have been due to an arrhythmia, whether any further referrals, investigations or changes in medication are necessary, or may be able to reassure you that it was a "simple faint" and that you simply need to know how to respond to warning symptoms (such as feeling hot, nauseous and lightheaded) if they happen again under similar circumstances.