Endocrine Abstracts (2006) 11 S11

Cardiac repercussions of thyroid hormones

JA Franklyn

University of Birmingam, Birmingham, United Kingdom.

The cardiovascular symptoms and signs of overt thyrotoxicosis are well known. These symptoms and signs may persist even after successful restoration of euthyroidism. Long-term, overt hyperthyroidism is associated with increased vascular mortality, from both cardiovascular and cerebrovascular causes, even in patients treated in the last 20 years. This mortality may particularly reflect an effect of thyroid hormone excess on cardiac rhythm, especially risk of atrial fibrillation. Subclinical thyroid hormone excess is also associated with subtle effects on cardiac physiology and increasing evidence suggests that this too translates into increased risk of atrial fibrillation and of vascular death. This in turn raises questions about the need to treat subclinical hyperthyroidism secondary to Graves’ disease or toxic nodular goitre.

Overt hypothyroidism also has cardiovascular consequences, although these are less well documented. Debate surrounds the question of whether subclinical hypothyroidism exerts an adverse on vascular risk, mediated by a minor adverse effect on the lipid profile, or via other mechanisms. Evidence from large-scale cohort studies is conflicting, some evidence suggesting an association of subclinical hypothyroidism with presence of atherosclerosis in elderly subjects. Further evidence is thus required to inform decisions about the need to correct subclinical hypothyroidism with thyroid hormone replacement.

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