[Prolonged ventricular repolarization measured by QTc interval in hyperthyroidism].

UNLABELLED: Thyroid dysfunction exerts an effect on cardiac function and on an electrocardiographic curve. Few studies analyzed the influence of thyroid hormones on heart repolarization. Heart repolarization is assessed in every-day-practice with corrected QT interval in ECG. Prolonged QTc is associated with increased risk for heart rythm disturbances and mortality. The aim of this study was to assess the effect of hyperthyroidism on heart repolarization, measured with QT corrected by Bazett's formula.

MATERIAL AND METHODS: The study group included 68 hyperthyroid patients (30 males, 38 females, mean age 39+/-10 yrs) and the controls were 39 in age and sex matched healthy subjects. TSH and free thyroxine were assessed. The QTc was measured in a standard 12 lead ECG.

RESULTS: In the study group the heart rhythm was faster when compared to controls (91.8 vs.73.7, SD+/-16.11, p<0.0001). The mean corrected QT (QTc) was 0.430, SD+/-0.0273 sec., in controls respectively: 0.414, SD+/-0.0208 sec., p<0.01. QTc did not correlate with free thyroxine concentrations (p=0.2785).

CONCLUSIONS: Corrected QT intervals were significantly prolonged in hyperthyroid patients, although they did not reach high values.