CARDIAC-FUNCTION IN THYROID-DISEASE - CLINICAL-FEATURES AND MANAGEMENT CONSIDERATIONS

Thyroid disease is often manifested by cardiac abnormalities. The site of the cardiac actions of thyroid hormone, whether from a direct, nuclear eff ect or an extranuclear effect, remains to be established. Nuclear effects are delayed 1/2 to 1 hour after administration of thyroid hormone, require ongoing protein synthesis, and are thought to result from the binding of thyroid hormone to two separate isoforms of the nuclear thyroid hormone receptor. This binding, which is specific to thyroid hormone response elements, stimulates transcription and results in translation of specific enzymes or contractile proteins. Extranuclear effects may influence plasma membrane transport of calcium, sugar, and amino acids in addition to directly influencing mitochondria and are very rapid, occurring within minutes. It is possible that there exists an interaction between the adrenergic system and the thyroid hormone system, which may also contribute to the cardiac actions of thyroid hormone. This review highlights the clinical manifestations of thyroid disease and the mechanisms of thyroid hormone involved in the cardiac abnormalities.