[Thyroid hormone and the cardiovascular system]

Thyroid hormone has many effects on the heart and vascular system. Many of the clinical manifestations of hyperthyroidism are due to the ability of thyroid hormone to alter cardiovascular hemodynamics. The hemodynamic effects of hypothyroidism are opposite to those of hyperthyroidism, although the clinical manifestations are less obvious. This review will integrate what is known about the mechanisms of thyroid hormone action on the heart with recent observations from both experimental and clinical studies of hyperthyroidism and hypothyroidism. Thyroid hormone has both direct and indirect actions on the cardiovascular system. Patients with thyroid disease, especially those with hyperthyroidism, often have symptoms and signs indicating changes in cardiovascular hemodynamics. Indeed, symptoms and signs referable to the cardiovascular system may be the only manifestations of thyroid dysfunction, and thyroid function should therefore be assessed by the measurement of serum thyrotropin concentrations in all patients with cardiovascular disease. Some suggest that the administration of triiodothyronine may benefit some patients with cardiovascular disease.