Subclinical hypothyroidism and Down's syndrome; studies on myocardial structure and function

Down syndrome and congenital heart disease: perioperative planning and management

Approximately 50% of newborns with Down syndrome have congenital heart disease. Non-cardiac comorbidities may also be present. Many of the principles and strategies of perioperative evaluation and management for patients with congenital heart disease apply to those with Down syndrome. Nevertheless, careful planning for cardiac surgery is required, evaluating for both cardiac and noncardiac disease, with careful consideration of the risk for pulmonary hypertension. In this manuscript, for children with Down syndrome and hemodynamically significant congenital heart disease, we will summarize the epidemiology of heart defects that warrant intervention. We will review perioperative planning for this unique population, including anesthetic considerations, common postoperative issues, nutritional strategies, and discharge planning. Special considerations for single ventricle palliation and heart transplantation evaluation will also be discussed. Overall, the risk of mortality with cardiac surgery in pediatric patients with Down syndrome is no more than the general population, except for those with functional single ventricle heart defects. Underlying comorbidities may contribute to postoperative complications and increased length of stay. A strong understanding of cardiac and non-cardiac considerations in children with Down syndrome will help clinicians optimize perioperative care and long-term outcomes.

Congenital Heart Disease and Thyroid Dysfunction: Combination, Association, and Implication

BACKGROUND

Patients with congenital heart disease have higher prevalence of thyroid dysfunction due to embryonic and genetic coexistence. Marked changes in cardiac function occur secondary to alternations in thyroid hormone levels. Cardiac catheterizations or cardiac surgeries with cardiopulmonary bypass can cause abnormalities in the circulating hormones, in the absence of primary thyroid disease. Therefore, monitoring of thyroid function should be routinely performed in children with congenital heart disease. Thyroid hormone supplementation has been postulated as a possible therapeutic option; however, the therapeutic decisions should be made based on individual circumstances, symptoms, and the severity of the thyroid dysfunction.

OBJECTIVES

To describe the correlation between congenital heart disease in children and thyroid dysfunction and the debate on monitoring, intervention, and treatment.

METHODS

PubMed, Clinical Key, and the Cochrane Library were searched using keywords relevant to congenital heart disease/surgery, cardiopulmonary bypass, thyroid hormones, sick euthyroid syndrome, and cardiac catheterization. Studies were limited to the English language and to children 0 to 18 years old. Studies in adults with important findings were reviewed as well. All clinical studies believed to have relevance were considered. All relevant studies were reviewed, and the most pertinent data were incorporated in this review.

CONCLUSION

There is lack of significant evidence concerning treatment for thyroid dysfunction in children with a congenital cardiac diagnosis. Adequately powered studies are needed before a uniform recommendation about treatment can be made.

Cardiovascular Risk Factors in Children and Adolescents with Subclinical Hypothyroidism

BACKGROUND

Subclinical hypothyroidism (SCH) is a commonly encountered entity in day-to-day clinical practice and has been associated with adverse cardiovascular risk profile in adults and children. Data on children and adolescents with SCH, from India, are limited.

MATERIALS AND METHODS

This study was a cross-sectional case-control study, conducted at a tertiary care center in Northeast India. Twenty-seven children and adolescents aged 11 ± 2.4 years with SCH and thyroid-stimulating hormone >7.5 mIU/L were included in the study along with 20 age-, gender-, and height-matched controls. Multiple clinical, biochemical, and radiological cardiovascular risk factors were assessed and compared between the two groups.

RESULTS

Body mass index (BMI) (P = 0.048), waist circumference (P = 0.008), waist to height ratio (P = 0.007), low-density lipoprotein cholesterol (P = 0.04), triglycerides (TGs) (P = 0.038), TGs to high-density lipoprotein (HDL) cholesterol ratio (P = 0.005), non-HDL cholesterol (P = 0.019), fasting insulin (P = 0.006), and homeostasis model assessment of insulin resistance (P = 0.007) were found to be significantly higher while free T4 (P = 0.002) and HDL cholesterol (P = 0.019) were found to be significantly lower in SCH subjects compared to controls. On multiple regression analysis, BMI was found to have significant association with multiple cardiovascular risk factors.

CONCLUSION

Children and adolescents with SCH were found to have adverse cardiovascular risk profile. Long-term follow-up studies are required to assess the clinical significance of these findings and requirement for therapy.

Subclinical hypothyroidism in childhood - current knowledge and open issues

Subclinical hypothyroidism is defined as serum levels of TSH above the upper limit of the reference range, in the presence of normal concentrations of total T₄ or free T₄. This biochemical profile might be an indication of mild hypothyroidism, with a potential increased risk of metabolic abnormalities and cardiovascular disease recorded among adults. Whether subclinical hypothyroidism results in adverse health outcomes among children is a matter of debate and so management of this condition remains challenging. Mild forms of untreated subclinical hypothyroidism do not seem to be associated with impairments in growth, bone health or neurocognitive outcome. However, ongoing scientific investigations have highlighted the presence of subtle proatherogenic abnormalities among children with modest elevations in their TSH levels. Although current findings are insufficient to recommend levothyroxine treatment for all children with mild asymptomatic forms of subclinical hypothyroidism, they highlight the potential need for assessment of cardiovascular risk among children with this condition. Increased understanding of the early metabolic risk factors associated with subclinical hypothyroidism in childhood will help to improve the management of affected individuals.

The effect of L-thyroxine treatment on left ventricular functions in children with subclinical hypothyroidism

OBJECTIVE

The aim of this study was to search for evidence suggesting treatment for childhood subclinical hypothyroidism (SH) by evaluating left ventricular (LV) functions of children with SH by using M-mode and tissue Doppler echocardiography (TDE).

METHODS

Children with SH and euthyroid healthy children (control group) were enrolled in the study. At baseline and 6 months after euthyroidism was achieved, M-mode and TDE were performed and LV functions were evaluated. Pretreatment parameters of the SH group were compared with those of controls and post-treatment parameters.

RESULTS

31 children with SH and 32 euthyroid healthy children were enrolled in the study. The groups had similar age, gender, puberty and body mass index. Interventricular septum thickness and LV mass index, which are the parameters for LV morphology, were slightly increased in the SH group than in the controls (p<0.05). In TDE, children with SH had significant changes in LV diastolic (lower E'm, higher E/E'm ratio and longer isovolumic relaxation time) and systolic functions (lower isovolumic contraction time) compared with controls (p<0.05). Six months after euthyroidism was achieved, TDE showed a significant improvement of some of the diastolic and systolic parameters (p<0.05).

CONCLUSIONS

The results of this study showed that SH is associated with subclinical alterations in LV function, and LT4 replacement may improve LV systolic and diastolic parameters. However, since SH is usually a self-limiting process, these improvements in LV functions may simply be associated with the natural course of the disease and/or physiological linear growth of the children.

Impact of obesity and Down syndrome on peak heart rate and aerobic capacity in youth and adults

Individuals with Down syndrome (DS) exhibit reduced aerobic capacity with reduced peak heart rate (HR_peak). This condition is often coexistent with higher level of obesity compared to individuals without DS. The purpose of this study is to investigate the effects of obesity and Down syndrome (DS) on peak heart rate (HR_peak) and peak oxygen consumption (VO_2peak) in children and adults both with and without intellectual disabilities (ID)s. VO_2peak and HR_peak from individualized treadmill tests on 654 individuals were analyzed. Body mass index was used to categorize individuals' weight status using standard cut-offs. DS groups had the lowest HR_peak (167bpm±14, p<0.05) compared to individuals with (183bpm±12) without ID (187bpm±12). Obesity did not affect HR_peak among adults and children with DS. VO_2peak was lower among individuals with DS (25.2mL/kg/min±6.3, p<0.05) when compared individuals with (37.0mL/kg/min±10.5) and without ID (36.1mL/kg/min±10.4). Obese adults with DS had lower VO_2peak (24.3mL/kg/min±6.9, p=0.001) compared to the normal weight (26.7±7.1mL/kg/min) and overweight groups (27.0mL/kg/min±6.1) with DS. Conversely, in children, obesity level did not impact VO_2peak in individuals with DS. Our results suggest that DS attenuates both VO_2peak and HR_peak, regardless of obesity status and age group. However, obesity was associated with lower VO_2peak in all adults, but not in children with DS.

Intensive Care and Perioperative Management of Patients With Complete Atrioventricular Septal Defect

Operative repair of an atrioventricular septal defect is not without risk. The purpose of this review is to highlight various key topics in the perioperative treatment of patients with atrioventricular septal defects, including challenges related to Down syndrome, postoperative arrhythmias, pulmonary hypertension, hypothyroidism, postoperative residual and recurrent lesions, including systemic atrioventricular valvar regurgitation and left ventricular outflow tract obstruction, sedation and analgesia, and vascular access.

Down syndrome: a cardiovascular perspective

This review focuses on the heart and vascular system in patients with Down syndrome. A clear knowledge on the wide spectrum of various abnormalities associated with this syndrome is essential for skillful management of cardiac problems in patients with Down syndrome. Epidemiology of congenital heart defects, cardiovascular aspects and thyroid-related cardiac impairment in patients with Down syndrome will be discussed.

The clinical significance of subclinical thyroid dysfunction

Subclinical thyroid disease (SCTD) is defined as serum free T(4) and free T(3) levels within their respective reference ranges in the presence of abnormal serum TSH levels. SCTD is being diagnosed more frequently in clinical practice in young and middle-aged people as well as in the elderly. However, the clinical significance of subclinical thyroid dysfunction is much debated. Subclinical hyper- and hypothyroidism can have repercussions on the cardiovascular system and bone, as well as on other organs and systems. However, the treatment and management of SCTD and population screening are controversial despite the potential risk of progression to overt disease, and there is no consensus on the thyroid hormone and thyrotropin cutoff values at which treatment should be contemplated. Opinions differ regarding tissue effects, symptoms, signs, and cardiovascular risk. Here, we critically review the data on the prevalence and progression of SCTD, its tissue effects, and its prognostic implications. We also examine the mechanisms underlying tissue alterations in SCTD and the effects of replacement therapy on progression and tissue parameters. Lastly, we address the issue of the need to treat slight thyroid hormone deficiency or excess in relation to the patient's age.

Longitudinal study of thyroid function in Down's syndrome in the first two decades

AIMS AND METHODS

Thyroid function tests were initially carried out on 122 children with Down's syndrome aged 6-14 years and then repeated four to six years later in 103 adolescents (85% of the group of 122) when they were aged 10-20 years (median 14.4 years). At the second test two were hypothyroid and two with isolated raised thyroid stimulating hormone (IR-TSH) were receiving thyroxine.

RESULTS

At the first test there were 98 (80%) euthyroid children: 83 were retested and four (5%) had IR-TSH. At the first test 24 had IR-TSH: 20 were retested and 14 (70%) had become normal. Seventeen with IR-TSH on initial testing had a thyrotrophin releasing hormone test within three months; TSH had become normal in eight (47%) of these children. There was no association between reported clinical symptoms and IR-TSH, but there were clear symptoms in one of the two with definite hypothyroidism.

CONCLUSIONS

The likelihood ratio for a positive result on second testing when raised TSH and positive antibody status on first testing are combined is 20. This suggests initial testing results could be used as a basis to select a subgroup for further testing at say five yearly intervals unless new symptoms emerge in the interim. It also suggests that yearly screening (as recommended by the American Academy of Pediatrics, 2001) is probably not justified in the first 20 years of life.