Background: At 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).
Objectives: Because 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.
Methods: Standard 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 (alpha(L)) and descending slopes (alpha(R)) 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).
Results: Logistic regression selected three parameters: QT, RR interval, and alpha(L) 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 alpha(L.)
Conclusion: Abnormal 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).