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Context Turner syndrome (TS) is a genetic condition and reported to be associated with a prolonged rate-corrected QT interval (QTc). Objectives To evaluate the prevalence of QTc prolongation in patients with TS, to compare their QTc intervals with healthy controls, and to investigate whether QTc prolongation is associated with a monosomy 45,X karyotype. Methods Girls (n=101) and women (n=251) with TS visiting our expertise center from 2004-2018 were included in this cross-sectional study. QT intervals of 12-leaded electrocardiograms were measured manually, using Bazett’s and Hodges’ formulas to correct for heart rate. A QTc interval of >450 ms for girls and >460 ms for women was considered prolonged. QTc intervals of patients with TS were compared to the QTc intervals of healthy girls and women from the same age-groups derived from the literature. Results In total, 5% of the population with TS had a prolonged QTc interval using Bazett’s formula and 0% using Hodges’ formula. Mean QTc intervals of these patients were not prolonged compared to the QTc interval of healthy individuals from the literature. Girls showed shorter mean QTc intervals compared to women. We found no association between monosomy 45,X and prolongation of the QTc interval. Conclusions This study shows that the QTc interval in girls and women with TS is not prolonged compared to the general population derived from the literature, using both Bazett’s and Hodges’ formulas. Furthermore, girls show shorter QTc intervals compared to women, and a monosomy 45,X karyotype is not associated with QTc prolongation.

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Turner syndrome (TS) is a chromosomal condition which is associated with an increased prevalence of cardiac morbidity and mortality. In this cross-sectional study, Minnesotabased electrocardiographic (ECG) abnormalities, aortic dimensions, routine-and myocardial strain echocardiographic parameters, and karyotype-cardiac phenotype associations were assessed in girls with TS. In total, 101 girls with TS (0-18 years) were included.The prevalence of major ECG abnormalities was 2% (T-wave abnormalities) and 39% had minor ECG abnormalities. Dilatation of the ascending aorta (z-score > 2) was present in 16%, but the prevalence was much lower when using TS-specific z-scores. No left ventricular hypertrophy was detected and the age-matched global longitudinal strain was reduced in only 6% of the patients. Cardiac abnormalities seemed more common in patients with a non-mosaic 45,X karyotype compared with other karyotypes, although no statistically significant association was found. Lowering the frequency of echocardiography and ECG screening might be considered in girls with TS without cardiovascular malformations and/or risk factors for aortic dissection. Nevertheless, a large prospective study is needed to confirm our results. The appropriate z-score for the assessment of aortic dilatation remains an important knowledge gap. The karyotype was not significantly associated with the presence of cardiac abnormalities, therefore cardiac screening should not depend on karyotype alone.