In the past decade, the knowledge regarding the central role played by hormones, peptides, and other molecules on the cardiovascular system has grown at an exponential rate. It is now clear that the heart is not just a target organ for hormones and peptides, but actually has functions as an “endocrine organ,” playing a central role in fluid and electrolyte homeostasis (natriuretic peptides). Other organs also play a role, for example, the kidney (renin and erythropoietin), adipose tissue (leptin, adiponectin, and irisin), and the gut (cholecystokinin and incretins). Once in the circulation, hormones bind to receptors on target tissues to elicit biological effects. Target tissues for some hormones (eg, glucocorticoid, thyroid hormone) can be numerous, reflecting the wide distribution of receptors, while other tissues may have a more limited distribution (eg, androgens). Because hormone receptors can be so ubiquitous throughout the body, the presence or absence of a single hormone can have multiple effects on one or more organ systems, including the cardiovascular system. Thus, almost all endocrine diseases, if left untreated or uncontrolled, can have cardiovascular manifestations. Treatment with hormones is a controversial topic in many areas, as large, prospective, randomized trials are lacking or provide conflicting results; for example, use of hormone replacement therapy for postmenopausal women has been recognized to have important cardiovascular complications, and there is a need to further address long-term safety for use in different patient groups. This chapter considers most of the common and some uncommon endocrinopathies that can affect the heart. We are becoming aware of the fact that the endocrine system and the cardiovascular system closely interact in regard to cardiovascular health and disease.
The cardiovascular signs and symptoms of thyroid disease are some of the most characteristic and clinically relevant signs and symptoms seen. Both hyperthyroidism and hypothyroidism produce changes in cardiac contractility, myocardial oxygen consumption, cardiac output, blood pressure, and systemic vascular resistance. Although it is well known that hyperthyroidism can produce atrial fibrillation, it is less well recognized that hypothyroidism predisposes to ventricular dysrhythmias. The importance of the recognition of the effects of thyroid disease on the heart is highlighted by the recognition that restoration of normal thyroid function in almost all cases reverses the abnormal cardiovascular changes.
Thyroid disease is quite common, affecting approximately 9–15% of the adult female population and a smaller percentage of males. This sex-specific prevalence likely results from autoimmune causes for the most common forms of thyroid disease, such as Graves and Hashimoto disease. However, with advancing age, especially beyond the eighth decade of life, the incidence of disease in men increases to equal that of women.
Thyroid hormone regulates oxidative and metabolic processes throughout the body by directing cellular protein synthesis at the nuclear level. Nongenomic actions of thyroid hormones have also been recognized based on rapid tissue responses that take place before RNA transcription could occur ...