Hyperthyroidism in patients with ischaemic heart disease after iodine load induced by coronary angiography: Long-term follow-up and influence of baseline thyroid functional status.

OBJECTIVE: To study the effect of a iodine load on thyroid function of patients with ischaemic heart disease (IHD) and the long-term influence of unknown subclinical hyperthyroidism.

CONTEXT: Subclinical hyperthyroidism is considered an independent risk factors for cardiovascular morbidity of patients with IHD. They routinely undergo coronary angiography with iodine contrast media (ICM) which may induce or even worsen hyperthyroidism.

DESIGN: A cross-sectional study followed by a longitudinal study on patients with subclinical hyperthyroidism.

PATIENTS: 810 consecutive IHD outpatients without known thyroid diseases or treatment with drugs influencing thyroid activity undergoing elective coronary angiography.

MEASUREMENTS: We evaluated thyroid function either before and 1 month after ICM; patients with thyrotoxicosis at baseline or after ICM were then followed up for 1 year.

RESULTS: 58 patients had hyperthyroidism at baseline (HB, 7.2%), independently associated to FT4 levels, thyroid nodules and family history of thyroid diseases. After ICM, the prevalence of hyperthyroidism was 81 (10%). Hyperthyroidism after ICM was positively predicted by baseline fT4 levels, thyroid nodules, age over 60, male gender, family history of thyroid diseases. Three months after ICM, 34 patients (4.2%) still showed hyperthyroidism (22 from HB, 13 treated with methimazole). One year after ICM, hyperthyroidism was still present in 20 patients (2.5%, all from HB, 13 treated).

CONCLUSIONS: The prevalence of spontaneous subclinical hyperthyroidism in IHD is surprisingly elevated and is further increased by iodine load, particularly in patients with thyroid nodules and familial history of thyroid diseases, persisting in a not negligible number of them even after one year.