Repolarization morphology in adult LQT2 carriers with borderline prolonged QTc interval

BackgroundAt least 50% of LQT2 carriers have borderline QTc (0.42–0.47 s), and they present a diagnostic difficulty to clinicians evaluating patients suspected of having long QT syndrome (LQTS).ObjectivesBecause QTc in this borderline range is nondiagnostic, the purpose of this study was to investigate whether analysis of phenotypic features of T-wave morphology could help identify LQT2 carriers with normal or near-normal QTc-interval duration.MethodsStandard 12-lead ECGs recorded without beta-blockers from LQT2 carriers (n = 90, 33 ± 14 years, 61% female) and noncarriers (n = 69, 38 ± 17 years, 58% female) were digitized. The following parameters were automatically measured: RR interval, QT/QTc, QT apex, T-wave amplitude, ascending (αL) and descending slopes (αR) of the T wave, and T-wave symmetry. We used a linear logistic regression model to identify the most relevant parameters for separating LQT2 carriers from noncarriers, within the overall population and among patients without overt QTc prolongation (390 ≤ QTc ≤ 470).ResultsLogistic regression selected three parameters: QT, RR interval, and αL in all models. In the overall population, the model provided 92.7% sensitivity and 90.0% specificity. In the group of patients without beta-blockers and near-normal QTc interval, 92.0% sensitivity (n = 46) and 81.4% specificity (n = 49) were achieved by the model including αL.ConclusionAbnormal T-wave morphology is a phenotypic expression of LQT2, and its quantification could be used to identify patients with suspected LQTS who do not have overt QTc prolongation (QTc >470).