Heartbeat syndrome often overlooked.

A heart-rhythm abnormality once thought quite rare may actually be a leading cause of unexpected death in children and young adults, according to one researcher.

The Long QT Syndrome gets its name from the prolonged QT interval that shows up on an electrocardiogram, a test that records the heart's electrical impulses. Many doctors, including cardiologists, miss or never see that clue to the lethal condition, says G. Michael Vincent of the University of Utah School of Medicine in Salt Lake City.

Typically, the only symptom of the abnormality is a very fast and irregular heartbeat that surfaces during times of excRement or physical exertion, Often, children or adults with this rapid heartbeat will lose consciousness. Sometimes, the heart regains a normal rhythm on its own. In other cases, the erratic heartbeat persists, causing death.

The condition is inherited -- often people with the syndrome have a family history of unexplained, sudden cardiac death. Recently, researchers identified a genetic marker for the condition, Vincent notes.

When people have a very obviously prolonged QT segment on an electrocardiogram and a family history of sudden cardiac death, the diagnosis proves relatively straightforward, Vincent says. However, many with this syndrome have heart function that appears completely normal during an electrocardiogram taken at rest. Often, abnormal electrocardiogram readings surface only during physical exertion, he explains.

The disorder need not be fatal, Vincent stresses. He points out that a variety of medications and treatments now exist for people with Long QT Syndrome. For example, beta-blocker drugs often can prevent the onset of a dangerously irregular heart rhythm, he says.