Thyroidal response following iodine excess for cardiac catheterisation and intervention in early infancy

Risks of Iodine Excess

Iodine is a micronutrient that is required for thyroid hormone synthesis. The iodide cycle in thyroid hormone synthesis consists of a series of transport, oxidation, organification, and binding/coupling steps in thyroid follicular cells. Common sources of iodine include the consumption of an iodine-rich diet or iodine fortified foods, the administration of amiodarone, iodine-containing supplements, or iodinated contrast media, and other miscellaneous sources. Methods to assess population iodine status include the measurement of urinary iodine concentrations, blood thyroglobulin levels, prevalence of elevated neonatal TSH levels, and thyroid volume. Although excessive iodine intake or exposure is generally well tolerated, an acute iodine load may result in thyroid dysfunction (hypothyroidism or hyperthyroidism) in certain susceptible individuals due to the failure to escape from the Wolff-Chaikoff effect and to the Jod-Basedow phenomenon, respectively. In this review, we discuss the associations between excessive iodine intake or exposure, with particular focus on iodinated contrast media as a common source of excess iodine in healthcare settings, and risks of incident thyroid dysfunction. We also summarize the risks of iodine excess in vulnerable populations and review current guidelines regarding the screening and monitoring of iodinated contrast-induced thyroid dysfunction. Finally, we discuss the long-term potential nonthyroidal health risks associated with iodine excess and suggest the need for more data to define safe upper limits for iodine intake, particularly in high-risk populations.

The Role of Iodine for Thyroid Function in Lactating Women and Infants

Iodine is a micronutrient needed for the production of thyroid hormones, which regulate metabolism, growth, and development. Iodine deficiency or excess may alter the thyroid hormone synthesis. The potential effects on infant development depend on the degree, timing, and duration of exposure. The iodine requirement is particularly high during infancy because of elevated thyroid hormone turnover. Breastfed infants rely on iodine provided by human milk, but the iodine concentration in breast milk is determined by the maternal iodine intake. Diets in many countries cannot provide sufficient iodine, and deficiency is prevented by iodine fortification of salt. However, the coverage of iodized salt varies between countries. Epidemiological data suggest large differences in the iodine intake in lactating women, infants, and toddlers worldwide, ranging from deficient to excessive intake. In this review, we provide an overview of the current knowledge and recent advances in the understanding of iodine nutrition and its association with thyroid function in lactating women, infants, and toddlers. We discuss risk factors for iodine malnutrition and the impact of targeted intervention strategies on these vulnerable population groups. We highlight the importance of appropriate definitions of optimal iodine nutrition and the need for more data assessing the risk of mild iodine deficiency for thyroid disorders during the first 2 years in life.

Prognostic Relevance of Thyroid Disorders in Adults With Congenital Heart Disease

Adults with congenital heart disease (ACHD) are frequently affected by thyroid diseases (TDs). However, the clinical relevance of TD in ACHD remains unknown. We aimed to describe the prevalence of TD in the ACHD population and to ascertain whether TD are associated with worse outcome. Patients with ACHD >18 years attending our tertiary center for a day-case between 2014 and 2019 were included. Clinical data between patients' first visit and December 2020 were collected. Primary end point was a combination of death, hospitalization for heart failure (HF), and new-onset of arrhythmic events. Secondary end points were each part of the primary outcome as separate end points. A total of 495 patients with ACHD (32.2 [24.5 to 45.6] years; 54% women) were included. Median follow-up was 9.4 (4.5 to 13.1) years. The prevalence of TD was 30%. TD group showed worse clinical status, as demonstrated by N-terminal pro b-type natriuretic peptide values (243.5 [96.5 to 523] vs 94 [45 to 207] pg/ml, p <0.001) and New York Heart Association class (27% vs 13% in class III to IV, p <0.0001) with higher incident rate of adverse events at follow-up (4.45 [3.43 to 5.69] % vs 1.29[0.94 to 1.75] % per person-year, p <0.001). TD were independently associated with higher risk of death (hazard ratio [HR] 4.1, p = 0.009), arrhythmic events (HR 3.8, p <0.0001), and hospitalization for HF (HR 8.02, p <0.0001). There was a fourfold increased risk of primary end point in the TD group even after propensity score matching for clinical variables including age, gender, disease complexity, physiological stage, previous palliative surgery, ventricular function, pulmonary arterial hypertension, cyanosis, and presence of systemic right ventricle (HR 4.47, p <0.0001). In conclusion, TD are predictive of adverse outcome in the ACHD population. Routine screening of thyroid function during follow-up in this population may be helpful to identify those with higher risk of death, arrhythmias, and HF.

Frequency of thyroid dysfunction in pediatric patients with congenital heart disease exposed to iodinated contrast media - a long-term observational study

Background The thyroid gland of patients with congenital heart disease may be exposed to large doses of iodine from various sources. We assessed the thyroid response after iodine exposure during conventional angiography in cardiac catheterization and angiographic computer tomography in childhood. Methods Retrospective mid- to long-term follow-up of 104 individuals (24% neonates, 51% infants, 25% children) with a median age and body weight of 104 days [0-8 years] and 5.3 kg [1.6-20]. Serum levels of thyroid-stimulating hormone, free triiodthyronine and free thyroxine were evaluated at baseline and after excess iodine. We also assessed risk factors that may affect thyroid dysfunction. Results Baseline thyroidal levels were within normal range in all patients. The mean cumulative iodinate contrast load was 6.6 ± 1.6 mL/kg. In fact, 75% had experienced more than one event involving iodine exposure, whose median frequency was three times per patient [1-12]. During the median three years follow-up period [0.5-10], the incidence of thyroid dysfunction was 15.4% (n=16). Those patients developed acquired hypothyroidism (transient n=14, long-lasting n=2 [both died]) with 10 of them requiring temporary replacement therapy for transient thyroid dysfunction, while four patients recovered spontaneously. 88 individuals (84.6%) remained euthyroid. Repeated cardiac interventions, use of drugs that interfere with the thyroid and treatment in the intensive care unit at the index date were strong predictors for acquired thyroid dysfunction. Conclusions The incidence of acquired hypothyroidism after iodine excess was 15.4%. However, most patients developed only transient hypothyroidism. Systemic iodine exposure seems to be clinically and metabolically well tolerated during long-term follow-up.

Iodinated contrast media and their effect on thyroid function - Routines and practices among diagnostic imaging departments in Norway

INTRODUCTION

In order to minimise adverse effects or patient injuries related to the effect of iodinated contrast media (ICM) on the thyroid, international guidelines and research recommend developing routines for identification and management of patients at risk of developing a thyroid dysfunction. This study aimed to investigate thyroid-related ICM administration practices among diagnostic imaging departments in Norway.

METHODS

The cross-sectional survey included 24 hospitals and 75 respondents with a 69% response rate. The survey covered practices for assessment and management of at-risk patients and the participants' perceived rationale for the routines.

RESULTS

The use of written checklists as recommended by international guidelines was quite modest (15%) and the respondents preferred various methods to identify risk and contraindications. Only 20% reported checking for any scheduled thyroid-scintigraphy and/or radioactive-iodine therapy. 42% indicated that they did not have thyroid-related ICM routines, and the main perceived reason was lack of knowledge on the topic. Radiographers and radiologists expressed uncertainty about each other's roles and routines.

CONCLUSION

This study revealed the need of optimisation of routines regarding ICM administration to patients at risk for thyroid dysfunction.

Excess iodine intake: sources, assessment, and effects on thyroid function

Iodine is essential for thyroid hormone synthesis. High iodine intakes are well tolerated by most healthy individuals, but in some people, excess iodine intakes may precipitate hyperthyroidism, hypothyroidism, goiter, and/or thyroid autoimmunity. Individuals with preexisting thyroid disease or those previously exposed to iodine deficiency may be more susceptible to thyroid disorders due to an increase in iodine intake, in some cases at intakes only slightly above physiological needs. Thyroid dysfunction due to excess iodine intake is usually mild and transient, but iodine-induced hyperthyroidism can be life-threatening in some individuals. At the population level, excess iodine intakes may arise from consumption of overiodized salt, drinking water, animal milk rich in iodine, certain seaweeds, iodine-containing dietary supplements, and from a combination of these sources. The median urinary iodine concentration (UIC) of a population reflects the total iodine intake from all sources and can accurately identify populations with excessive iodine intakes. Our review describes the association between excess iodine intake and thyroid function. We outline potential sources of excess iodine intake and the physiological responses and consequences of excess iodine intakes. We provide guidance on choice of biomarkers to assess iodine intake, with an emphasis on the UIC and thyroglobulin.

Effect of iodinated contrast medium on thyroid function: a study in children undergoing cardiac computed tomography

BACKGROUND

Few studies, and with conflicting results, have evaluated the potential effects of iodinated contrast media on children's thyroid function.

OBJECTIVE

To investigate the effects of iodinated contrast medium on thyroid function in neonates, infants and young children with congenital heart disease undergoing cardiac computed tomography (CT).

MATERIALS AND METHODS

We retrospectively evaluated 10 neonates (group 1) and 23 infants and young children (group 2) without thyroid or renal disease for serum levels of thyroid-stimulating hormone, free triiodothyronine and free thyroxine before contrast-enhanced cardiac CT, 48 h after CT and at discharge from the hospital. Cardiac CT was performed with intravenous administration of 1.14±0.17 mL/kg of body weight of iopromide (containing 370 mg of iodine/mL).

RESULTS

Group 1 had a reduction of thyroid-stimulating hormone from baseline to 48 h post injection (P=0.002). Group 2 had a reduction of thyroid-stimulating hormone median levels from baseline to 48 h post injection and an increase from 48 h to discharge (P=0.0005 and P=0.0001, respectively).

CONCLUSION

Intravenous iodinated contrast medium in children with congenital heart disease caused transient thyroid-stimulating hormone decrease 48 h after CT, with thyroid-stimulating hormone returning to normal range at discharge.