Cardiac effects of L-thyroxine administration in borderline hypothyroidism.

OBJECTIVE: To investigate the clinical relevance of l-thyroxine (l-T(4)) substitution therapy in borderline hypothyroidism. DESIGN: To assess whether and to what extent administration of l-T(4) is able to modify systolic and diastolic function in patients with subclinical hypothyroidism and in subjects with autoimmune thyroiditis and normal serum TSH. METHODS: We studied 26 patients with classical Hashimoto's thyroiditis [18 with increased serum TSH (>3 mU/ml - Group A), and 8 with normal serum TSH (<3 mU/ml) - Group B]; a third group (C) included 13 healthy controls. All subjects underwent Pulsed Wave Tissue Doppler Imaging (PWTDI) to accurately quantify the global and regional left ventricular function. RESULTS: In both groups A and B we confirmed a significant impairment of systolic ejection (p<0.001 and p<0.05, respectively), a delay in diastolic relaxation (p<0.001 and p<0.05, respectively) and a decrease in the compliance to the ventricular filling (p<0.05). Administration of 50 microg/day of l-T(4) produced a progressive reduction of serum TSH (within the normal range) and normalization of all PWTDI parameters, which began after 6 months and finished after 12 months. CONCLUSION: Our data confirm previous evidence that subclinical hypothyroidism is associated with a cardiac dysfunction, even when this is very mild (i.e. with serum TSH still comprised in the normal range), and show that these abnormalities are reversible with l-T(4) replacement therapy.

Cardiac function in borderline hypothyroidism: a study by pulsed wave tissue Doppler imaging.

OBJECTIVE: In subclinical hypothyroidism (SH), impaired diastolic function has been documented at rest and on effort, while systolic dysfunction has only been assessed on effort. DESIGN: The aim of the present study was: (a) to further assess systolic function at rest in SH; and (b) to ascertain whether cardiac dysfunction could precede TSH increase in euthyroid patients with a high risk of developing SH. METHODS: We studied 32 patients with classical Hashimoto's thyroiditis (22 with increased serum TSH (> 3 mU/ml - group A), and 10 with normal serum TSH (< 3 mU/ml - group B)); a third group (C), which included 13 healthy controls. All subjects underwent pulsed wave tissue Doppler imaging (PWTDI) to accurately quantify the global and regional left ventricular function. RESULTS: When compared with group C, PWTDI indices showed that in both groups A and B there was a significant impairment of systolic ejection (P < 0.001 and P < 0.05, respectively), a delay in diastolic relaxation (P < 0.001 and P < 0.05, respectively) and a decrease in the compliance to the ventricular filling (P < 0.05). Several significant correlations were found between PWTDI parameters and serum-free T(3) and T(4) and TSH concentrations. CONCLUSION: PWTDI is a sensitive technique that allows detection of both diastolic and systolic abnormalities, not only in patients with SH, but also in euthyroid subjects with a high risk of developing thyroid failure. Futhermore, the significant correlations of several PWTDI indices with serum FT(3) and TSH concentrations strongly support the concept of a continuum spectrum of a slight thyroid failure in autoimmune thyroiditis extending to subjects with serum TSH still within the normal range.