Endocrine Abstracts

Introduction: Subclinical hyperthyroidism (SH) affects about 1% of population. The diagnosis of this disease leans on the laboratory criteria only: decreased of TSH and normal FT₃ and FT₄ levels. SH increases mortality mostly due to cardiovascular diseases including arrhythmia and overload of the heart. Enlarging of heart chambers is one of the cause of arrhythmia, and cardiac index is one of indicators of heart after load.

Aim: To estimate an influence of cure of SH on heart chambers diastolic volumes (left ventricle – LV, right ventricle – RV, left atrium LA) and cardiac index (CI) measured by echocardiography (echo) and to find the relationships between these parameters and TSH, FT₃ and FT₄ concentrations.

Method: Forty-four patients (37 women, 7 men) aged 45.9±11, with 12.8±9.8 month history of only autonomous endogenous SH (TSH=0.16±0.1 IU/l), were examined with echo twice: before and 5.7±4.2 months after TSH normalization (TSH=1.32±0.1 IU/l) with radioiodine treatment (dose 12.1±5.7 mCi). The average time between examinations was 12.5±6 months. The Local Ethical Committee approval has been obtained.

Results: The cure of SH caused decrease of LV (P=0.011), RV (P=0.010), LA (P<0.000) and CI (P<0.000). During SH the level of FT₃ was positively correlated with LA (P=0.008).

Conclusions: 1. Cure of autonomous subclinical hyperthyroidism with radioiodine decreases risk of atrial and ventricular arrhythmia, it also decreases heart after load.

2. In autonomous subclinical hyperthyroidism, the level of FT₃ positively correlates with left atrium diastolic diameter.

3. Above findings support the decision to treat endogenous subclinical hyperthyroidism.