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

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 LOTS patients (40 type 1 [LQT1], 42 type 2 [LOT2], 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 OTc stretching in identifying LOTS. RESULTS During maximal QT stretching, the T-wave morphologies that best discriminated LOTS 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 LOTS. 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 LOTS.