Cardiac effects of l-thyroxine administration in borderline hypothyroidism

ObjectiveTo investigate the clinical relevance of l-thyroxine (l-T4) substitution therapy in borderline hypothyroidism.DesignTo 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.MethodsWe 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.ResultsIn 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.ConclusionOur 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.