Test Identifies Children At Risk For Life-Threatening Rapid Heart Rhythm

November 10, 1997

ORLANDO, Nov. 10 -- A simple, widely available test may help identify young children at risk of developing life-threatening rapid heartbeats, report researchers today at the American Heart Association's 70th Scientific Sessions.

"In the 20 children we tested so far, the test appears to predict which children will develop the irregular heartbeat," says Ann Dubin, M.D., assistant professor of pediatrics at Stanford University Medical Center. "The test could give us a means to identify high-risk children early on and then follow them more closely and initiate appropriate treatment."

The irregularity, called intra-atrial re-entry tachycardia (IART), has been linked to an abnormal P wave, a period when the upper chamber of the heart is activated. A delay in the formation of the P wave predicts the risk of IART, a rapid heart beat also known as atrial flutter.

If the test proves accurate in a large number of children, physicians would have an important tool for evaluating and treating a potentially fatal heart condition in children. IART can cause the heart to beat so rapidly that cardiac arrest and death can occur, says Dubin. The rapidly contracting heart may also eject blood clots, which can travel through the bloodstream to the brain and cause a stroke.

The abnormality can be identified by studying electrocardiograms, graphs produced from the measurement of the heart's electrical activity. Electrocardiograms (ECG) are standard equipment in hospitals, clinics and many physicians' offices.

During a normal heartbeat, electrical impulses flow rapidly and uninterrupted from the upper chambers (atria) to the lower chambers (ventricles) of the heart. The impulses coordinate the contraction and relaxation of the heart muscle. In children born with congenital heart problems, the electrical activity may be altered, and IART is one possible consequence.

Currently tests used to predict the development of IART have been unreliable. To develop an accurate test, Dubin has studied ECG tracings from three types of children: those with congenital heart disease and IART; children with congenital heart disease but no IART; and children without heart disease. Among children with IART, tracings made before and after the irregularity developed showed that the children had a significantly longer delay in the formation of the P wave compared to the other two groups of children. This long delay is called P wave dispersion. IART was associated with a P-wave dispersion of at least 50 milliseconds (50 one-thousandths of a second). P-wave dispersion averaged about 20-30 milliseconds in the other two groups of children.

"Because we've studied so few children, I wouldn't want to say that the 50 millisecond cutoff will hold up in every case, but so far that cutoff has predicted the development of IART in every child we've studied," says Dubin.

American Heart Association

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