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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 the QT interval?
It is a measurement, made from the electrocardiogram (ECG or EKG). It reflects the duration of the electrical activity that controls contraction of the cells of the heart muscle.

Long QT Syndrome
Long QT syndrome refers to a condition in which there is an abnormally long QT interval on the electrocardiogram. It can be inherited ("congenital long QT") or induced by drugs or abnormal levels of the salts normally found in the blood, such as potassium and magnesium ("acquired long QT"). The inherited form occurs due to 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. Some people, despite having a normal QT interval under normal conditions, may develop a prolonged QT and associated rhythm abnormalities when taking certain medications; this tendency may also be inherited, and is the subject of our research effort. A list of drugs that prolong the QT interval or cause Torsades de Pointes can be found on our site at View the QT Drugs List.


Arizona Center for Education and Research on Therapeutics
The Critical Path Institute

Tucson, Arizona and Rockville, Maryland

Funded in part by Agency for Healthcare Research and Quality grant 1 U18 HS10385-01

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