heart and blood vessel disorders
Long QT Interval Syndromes
Diagnosis of Long QT Interval Syndromes
Electrocardiography (ECG) Usually exercise testing and ambulatory ECG monitoring Sometimes genetic testing A long QT interval may be found when an ECG is done for other reasons. People with unexplained cardiac arrest or fainting or a family history of such when the affected people do not have other heart disease are evaluated for long QT interval syndromes. Doctors typically do an ECG along with an exercise test and also have the person wear a heart monitor at home for several days or longer. Not all people with a long QT interval have congenital long QT syndrome, and not all people with a congenital long QT syndrome have a long QT interval on any given ECG. Thus, doctors use a scoring system based on the results of the tests and the person's symptoms to predict how likely the diagnosis is. The score helps determine which people need genetic testing or provocative testing. With provocative testing, people are given a drug to try to cause the characteristic long QT interval on the ECG. People with a low likelihood of having a congenital long QT interval syndrome do not need genetic testing, but when the likelihood is intermediate or high, genetic testing is needed. Close family membersof a person with congenital long QT syndrome should be examined by a doctor to detect symptoms that may suggest an abnormal heart rhythm and should undergo ECG. Genetic testing and exercise testing also are sometimes needed. 