Repolarization morphology in adult LQT2 carriers with borderline prolonged QTc interval.
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).


OBJECTIVE
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.)


CONCLUSIONS
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).
Couderc
Jean-Philippe
JP
Heart Research Follow-up Program, University of Rochester Medical Center, Rochester, New York.
McNitt
Scott
S
Xia
Jean
J
Zareba
Wojciech
W
Moss
Arthur J
AJ
D000200:Action Potentials; D000328:Adult; D000072237:ERG1 Potassium Channel; D004562:Electrocardiography; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics*; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate; D006801:Humans; D016015:Logistic Models; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000235:genetics / Q000503:physiopathology*; D008297:Male; D008955:Models, Cardiovascular; D009154:Mutation; D010641:Phenotype; D011237:Predictive Value of Tests; D012372:ROC Curve; D012107:Research Design; D012680:Sensitivity and Specificity; D013997:Time Factors
D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels