Journal
CIRCULATION
Volume 103, Issue 8, Pages 1095-1101Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1161/01.CIR.103.8.1095
Keywords
long-QT syndrome; genetics; electrocardiography
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Background-The 2 genes KCNQ1 (LQT1) and HERG (LQT2), encoding cardiac potassium channels, are the most common cause of the dominant long-QT syndrome (LQTS). In addition to QT-interval prolongation, notched T waves have been proposed as a phenotypic marker of LQTS patients. Methods and Results-The T-wave morphology of carriers of mutations in KCNQ1 (n=133) or HERG (n=57) and of 100 control, subjects was analyzed from Holter ECG recordings. Averaged T-wave templates were obtained at different cycle lengths, and potential notched T waves were classified as grade 1 (G1) in case of a bulge at or below the horizontal, whatever the amplitude, and as grade 2 (G2) in case of a protuberance above the horizontal. The highest grade obtained from a template defined the notch category of the subject. T-wave morphology was normal in the majority of LQT1 and control subjects compared with LQT2 (92%, 96%, and 19%, respectively, P<0.001). G1 notches were relatively more frequent in LQT2 (18% versus 8% [LQT1] and 4% [control], P<0.01), and G2 notches were seen exclusively in LQT2 (63%). Predictors for G2 were young age, missense mutations, and core domain mutations in HERG. Conclusions-This study provides novel evidence that Holter recording analysis is superior to the 12-lead ECG in detecting GI and G2 T-wave notches. These repolarization abnormalities are more indicative of LQT2 versus LQT1, with G2 notches being most specific and often reflecting HERG core domain missense mutations.
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