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Education in Heart
GENERAL CARDIOLOGY
Thyroid disease and the heart
  1. A D Toft,
  2. N A Boon
  1. Endocrine Clinic, and Department of Cardiology, Royal Infirmary, Edinburgh, UK
  1. Dr A D Toft, Endocrine Clinic, Royal Infirmary, Edinburgh EH3 9YW, UK

https://doi.org/10.1136/heart.84.4.455

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    Cardiologists encounter thyroid disorders frequently. Hyperthyroidism causes and may present with atrial fibrillation, while hypothyroidism is a risk factor for coronary artery disease. Moreover, the use of amiodarone may precipitate a variety of thyroid disorders, and severe heart disease, such as left ventricular failure or acute myocardial infarction, can cause confusing disturbances in thyroid function tests.

    Key points

    • Serious non-thyroidal illness, such as heart failure, can cause high T4 and low TSH concentrations, suggesting hyperthyroidism.

    • Measurements of T3 may help to exclude thyrotoxicosis in this situation but can be inconclusive, and in some situations a trial of antithyroid drugs may be warranted.

    • In view of these difficulties thyroid function tests should only be requested in patients with credible evidence of thyroid disease such as goitre or unexplained atrial fibrillation.

    Key points

    • Amiodarone will induce hyper- or hypothyroidism in up to 20% of subjects, and thyroid dysfunction may persist for several months or develop for the first time after the drug has been stopped.

    • Thyroid status should be evaluated thoroughly before introducing the drug because patients with pre-existing (often occult) thyroid disease are at particularly high risk.

    • T3 is the most valuable and sensitive measure of thyroid function in patients who have received amiodarone because, even among euthyroid patients, the inhibition of the peripheral conversion of T4 to T3 may produce a high T4 and low TSH.

    Hyperthyroidism

    Hyperthyroidism is a common condition with a prevalence of approximately 1%; it affects predominantly women aged 30–50 years and is usually (70%) caused by Graves' disease which is characterised by diffuse goitre, orbitopathy, pretibial myxoedema, and the presence of stimulating thyrotrophin (TSH) receptor antibody in the serum. Most of the remaining cases (20%) are caused by autonomous production of thyroid hormones by a nodular goitre.

    Effects of thyroid hormones on the cardiovascular system

    The thyroid secretes two active hormones: thyroxine (T4) which …

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