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Effect of Levothyroxine on Cardiac Function and Structure in Subclinical Hypothyroidism: A Double Blind, Placebo-Controlled Study

Department of Internal Medicine, University of Pisa School of Medicine, 56126 Pisa, Italy

Address all correspondence and requests for reprints to: Fabio Monzani, M.D., Department of Internal Medicine, University of Pisa, Via Roma 67, 56126 Pisa, Italy. E-mail: fmonzani{at}med.unipi.it

Subclinical hypothyroidism (sHT) affects 5–15% of the general population; however, the need of lifelong L-T₄ therapy is still controversial. As myocardium is a main target of thyroid hormone action, we investigated whether sHT induces cardiovascular alterations. Twenty sHT patients were randomly assigned to receive placebo or L-T₄ therapy and were followed for 1 yr. Twenty sex- and age-matched normal subjects served as controls. Doppler echocardiography and videodensitometric analysis were performed in all subjects. Myocardium textural parameters were obtained as mean gray levels, which were then used to calculate the cyclic variation index (CVI; percent systolic/diastolic change in mean gray levels).

Patients had a significantly higher isovolumic relaxation time (3.1 ± 0.5 vs. 2.6 ± 0.6; P < 0.03), peak A (0.77 ± 0.16 vs. 0.56 ± 0.13 m/s; P < 0.01), and preejection/ejection time (PEP/ET) ratio (0.72 ± 0.05 vs. 0.57 ± 0.06; P < 0.03) and a lower CVI (P < 0.0001) than controls. CVI was inversely related to TSH level (P < 0.0001) and PEP/ET ratio (P < 0.01). L-T₄-treated patients showed a significant reduction of the PEP/ET ratio (P < 0.05), peak A (P < 0.05), and isovolumic relaxation time (P < 0.05) along with a normalization of CVI. Conversely, no changes were observed in the placebo-treated group.

In conclusion, sHT affects both myocardial structure and contractility. These alterations may be reversed by L-T₄ therapy.

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