Endocrine Abstracts (2008) 16 P680

The influence of cure of subclinical hyperthyreosis on heart rate and autonomous nervous sytem

Grzegorz Kaminski, Karol Makowski, Agnieszka Dunal, Dariusz Michalkiewicz, Marlena Olszak, Zbigniew Podgajny & Leszek Kubik

Military Institute of Health Services, Warsaw, Poland.

Introduction: Subclinical hyperthyreosis (SH) affects about 1.5% population at least. The diagnosis of this disease leans on the laboratory criteria only: decreased of TSH and normal FT3 and FT4 levels. SH increases mortality and there is no unequivocal procedure algorithm to manage patients with this desease.

Aim: To estimate an influence of cure of SH on heart rate and on autonomous nervous sytem and to find the relationships between parameters of Holter electrocardiography (Holter) and of TSH, FT3 and FT4 levels.

Method: About 44 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 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) with the use of Holter and heart rate variability (HRV) evaluation. 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 mean heart rate (P=0.004), number of ventricular ectopic beats (P=0.048) and dispersion of Q-T interval in ecg (QTd) – P=0.02, and increase of activity of parasympathetic nervous sytem expressed as increase of rMSSD (P=0.03) and LF in horizontal body position (P=0.049). During SH the level of TSH was inversely correlated (P=0.048) but FT3 (P=0.017) and FT4 (P=0.004) were positively correlated with QTd.

Conclusions: 1. Cure of autonomous subclinical hypertyhreosis with radioiodine decreases risk of ventricular arrhythmia, and increases activity of parasympathetic nervous system. 2. In autonomous endogenous subclinical hyperthyreosis, the level of TSH inversely and FT3 i FT4 positively correlates with dispersion of Q-T interval in electrocardiogram. 3. Above changes support the decision to treat subclinical hyperthyreosis.

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