Evaluation of QT dispersion and Tp-e interval in children with subclinical hypothyroidism.

Background: Studies on adults have shown increased dispersion of QT and corrected QT (QTc), peak-to-end interval of the T wave (Tp-e), Tp-e/QT ratio, and Tp-e/QTc ratio in subclinical hypothyroidism (SH), but there have been no pediatric studies.

Materials And Methods: A total of 40 SH patients were compared with 40 healthy children in respect to serum thyroid-stimulating hormone (TSH), serum-free level of triiodothyronine, and free level of thyroxine (fT4). SH diagnosis was accepted as TSH above the laboratory accepted upper limit (>4.2 mU/L) and normal fT4 values. The patient and control group data were compared by calculating the QT interval, QTc, QT dispersion (QTd), QTc dispersion (QTcd), Tp-e, Tp-e/QT ratio, and Tp-e/QTc ratio on 12-lead surface electrocardiogram.

Results: The mean age was 7.91 ± 3.6 years in the SH group and 8.8 ± 2.4 years in the control group. In the SH group, the minimum QT (QTmin) was determined to be statistically significantly lower (P < 0.001) and maximum QT (QTmax), QTd, QTcd, Tp-e, Tp-e/QT ratio, and Tp-e/QTc ratio were statistically significantly higher (P = 0.028, P < 0.001, P = 0.003, P < 0.001, P = 0.001, P < 0.001, respectively). A positive correlation was determined between TSH and QTmax (r: +0.331, P = 0.037).

Conclusions: The current study is the first to have shown significantly increased QTd, QTcd, Tp-e, Tp-e/QT ratio, and Tp-e/QTc ratio in children diagnosed with SH. A positive correlation was determined between TSH and maximum QT values, Tp-e, Tp-e/QT ratio, and Tp-e/QTc ratio. These results suggest the need to further assess the long-term risks of prolonged QT dispersion in the setting of subclinical hypothyroidism.