[Influence of hyperthyroidism defined as TSH serum level on QT corrected interval dispersion (QTcd)]

Electrocardiographic dispersion reflects the heterogenity of ventricular repolarisation. It has been suggested that changes QT dispersion in thyroid dysfunction can be prognostic factor of different arrhytmias aspecially ventricular arrhytmias. Calculation can be done from easy availabe tests such as: TSH serum level and resting electrocardiogram.

The aim of the present study was to evaluate the prognostic value between TSH serum level, QT corrected interval value and corrected interval dispersion value.Are there any relationship between QTcd and TSH serum level.

From 314 person with hyperthyroidism included to the study group 46 patients with isolate hyperthyroidism whom have made TSH serum leve land resting electrocardiogram. In this group was 36 (78.3%) women and 10 (21.7%) men aged 38 to 78. The medium age was 52.3 +/- 9.9 years. To the observation include the patient with TSH level below 0,4 uU/ml in sreening. The results has been analysed in two subgroups: first A (1A)--high level hyperthyroidism (25 person; 18 women (72.0%), 7 men (28%); second B(2B)--low level hyperthyroidism (21 person; 18 85.7%)women, 7 men (14.3%).

In hyperthyroidism group (1A+1B) with TSH serum level below 0.4 uU/ml QTc dispersion increase. Relation seems to be inversely proportional. The lower TSH serum level the higher percent increasing distance of QTcd, especially in high level hyperthyroidism subgroup(1A) with TSH seru level below 0.1 uU/ml. For QTcd > or = 65 ms sensivity is 88.0%; specisicity is 42.9%. We didn't observe serious ventricular arrhytmias in the both subgroups.

Indeed there is evidence that invesigating QT c interval dispersion (QTcd) in thyroid dysfunction may be a useful parameter in hyperthyroidism especially in high level hyperthyroidism subgroup (1A). The long QTcd suggest proarythmic susceptibility in this subjects subhyperthyroidism group with another risk stratification predicts increasing QTcd such as dyselectrolytaemia, previous myocardial infarct, coronary artery disease, diabetes, stroke or antyarrhytmic drugs.