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Electrocardiogram Test for Long QT Syndrome Assessed

New test procedure seen as valuable in difficult diagnosis of this dangerous heart arrhythmia

THURSDAY, Jan. 28 (HealthDay News) -- The response of the QT interval to a sudden heart rate acceleration as seen on an electrocardiogram (ECG) offers diagnostic information helpful in the challenging diagnosis of long QT syndrome (LQTS), according to a study published online Jan. 27 in the Journal of the American College of Cardiology.

Sami Viskin, M.D., of Tel Aviv University in Israel, and colleagues obtained baseline ECGs in 68 patients with LQTS and 82 healthy controls. The testing procedure began with each subject being supine and at rest and then being asked to quickly stand up and remain still during the ECG. The researchers compared the QT interval at baseline and during maximal sinus tachycardia, maximal QT interval prolongation, and maximal QT interval stretching.

The researchers found that both the patients and control subjects had similar heart rate acceleration of 28 beats/min after quickly standing up. However, for the LQTS patients, the QT interval increased by 4 ms in response to the induced tachycardia, while the QT interval of the controls shortened by 21 ms. Because the interval between R waves of heartbeats shortened more than the QT interval during maximal tachycardia, the corrected QT interval was found to increase by 89 ms in the LQTS group and just 50 ms in the control group, providing diagnostic value.

"Evaluation of the response of the QT interval to the brisk tachycardia induced by standing provides important information that aids in the diagnosis of LQTS," the authors write.

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