[Subclinical hypothyroidism influences ventricular repolarization measured by QTc interval]

Thyroid disorders exert a major effect on cardiac function and on ECG. Few studies examined the effect of thyroid hormones on ventricular repolarization, measured by corrected QT interval (QTc). Prolonged QTc is associated with increased risk of arrythmias and cardiac mortality. The aim of this study was to examine the influence of subclinical hypothyroidism on ventricular repolarization measured by corrected QTc in standard 12-lead electrocardiogram. The examined group consisted of 32 patients with hypothyroidism, the controls were 39 healthy individuals. The mean corrected QTc was 0.434, SD +/- 0.0296 seconds and 0.414, SD +/- 0.0208 in the examined groups and in controls, respectively (p < 0.01). QTc did not correlate with free thyroxine concentrations (p = 0.4064). In the group with subclinical hypothyroidism we did not observe a significant difference in heart rate (74.3 vs. 73.7, SD +/- 13.58, NS).

Corrected QT intervals were significantly prolonged in patients with subclinical hypothyroidism.