Diagnostic value of T-wave morphology changes during "QT stretching" in patients with long QT syndrome

Abstract

Background: Specific T-wave patterns on the resting electrocardiogram (ECG) aid in diagnosing long QT syndrome (LQTS) and identifying the specific genotype. However, provocation tests often are required to establish a diagnosis when the QT interval is borderline at rest.

Objective: The purpose of this study was to determine whether T-wave morphology changes provoked by standing aid in the diagnosis of LQTS and determination of the genotype.

Methods: The quick-standing test was performed by 100 LQTS patients (40 type 1 [LQT1], 42 type 2 [LQT2], 18 type 3 [LQT3]) and 100 controls. Logistic regression was used to determine whether T-wave morphology changes provoked by standing added to the already established diagnostic value of QTc stretching in identifying LQTS.

Results: During maximal QT stretching, the T-wave morphologies that best discriminated LQTS from controls included "notched," "late-onset," and "biphasic" T waves. These 3 categories were grouped into a category named "abnormal T-wave response to standing." During quick standing, a QTc stretched ≥490 ms increased the odds of correctly identifying LQTS. T-wave morphology changes provoked by standing were most helpful for identifying LQT2, less helpful for LQT1, and least helpful for LQT3.

Conclusion: The sudden heart rate acceleration produced by abrupt standing not only increases the QTc but also exposes abnormal T waves that are valuable for diagnosing LQTS.

Keywords: Electrocardiogram; Long QT syndrome; QT interval; T-wave morphology.