Cardiac effects of l-thyroxine administration in borderline hypothyroidism

Objective To investigate the clinical relevance of l-thyroxine (l-T4) substitution therapy in borderline hypothyroidism. Design To assess whether and to what extent administration of l-T4 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 Hashimotoʹs 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 μg/day of l-T4 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-T4 replacement therapy.