How is a response to standing used in the workup of long QT syndrome (LQTS)?

Updated: Nov 29, 2017
  • Author: Ali A Sovari, MD, FACP, FACC; Chief Editor: Mikhael F El-Chami, MD  more...
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Answer

Viskin and colleagues demonstrated that the expected shortening of the QT interval in response to sinus tachycardia induced by standing from a supine position is impaired in patients with long QT syndrome (LQTS). [1] In fact, the QTc interval in patients with LQTS increased with standing position, and more premature ventricular contractions (PVCs) were detected during standing in these patients. Thus, the increased QTc interval in response to standing up, which is associated with increased sympathetic tone, can provide more diagnostic information in patients with LQTS. [1] The increase in QTc in response to standing may persist in patients with LQTS even after heart rate returns to normal. [2]

In addition, this study may reveal that standing up in patients with LQTS may be associated with more focal activities and ventricular arrhythmias. Therefore, syncope while standing up in a patient with LQTS may not be simply a vasovagal syncope but may represent a more dangerous condition.

In a more recent study, investigators evaluating the standing test in 36 congenital LQTS patients (LQT1, LQT2, LQT7, and unidentified genotypes) and 41 control subjects found that the corrected QT interval (QTc) obtained immediately after standing and the QTc change from baseline were significantly higher in the LQTS group than in the control group, and that these QTc evaluations had a high diagnostic value when compared to the baseline QTc. [23] In addition, the use of beta-blocker therapy ameliorated the standing response in the LQTS patients.


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