Endocrine Abstracts

Introduction: Subclinical hyperthyroidism (SH) affects about 1% of world human population at least. The diagnosis of this disease leans on the laboratory criteria only: decreased of TSH and normal FT₃ and FT₄ concentrations. SH increases mortality mostly due to cardiovascular diseases including overload of the heart and ventricular arrhythmia. These symptoms are anticipated by increasing of left ventricular walls thickness and its mass index.

Aim: To estimate an influence of cure of SH on left ventricular walls thickness: interventricular septum diameter (IVSD), posterior wall diameter (PWD) and left ventricular mass index (LVMI) measured by echocardiography. And also to find the correlations 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 mIU/l), were examined with echo twice: before and 5.7±4.2 months after TSH normalization (TSH=1.32±0.1 mIU/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 IVSD (P<0.00001), PWD (P<0.00001), LVMI (P<0.0001). During SH the level of FT₃ was positively correlated with IVSD (P=0.045) and PWD (P=0.038).

Conclusions: i) Cure of autonomous subclinical hyperthyroidism with radioiodine decreases left ventricular walls thickness and its mass index. ii) These results can indicate decrease of heart after load and the risk of ventricular arrhythmia. iii) In autonomous subclinical hyperthyroidism, the level of FT₃ positively correlates with diameter of interventricular septum and left ventricular posterior wall. iv) Above findings support the decision to treat endogenous subclinical hyperthyroidism especially in patients with cardiovascular risk.