Myocardial perfusion and intima-media thickness in patients with subclinical hypothyroidism

The Relationship between Subclinical Hypothyroidism and Carotid Intima-Media Thickness as a Potential Marker of Cardiovascular Risk: A Systematic Review and a Meta-Analysis

BACKGROUND AND OBJECTIVES

Thyroid dysfunction is known to have significant consequences on the cardiovascular system. The correlation between carotid intima-media thickness (CIMT) and subclinical hypothyroidism (SCH) has been frequently evaluated in clinical studies in recent years. This study aimed to evaluate the significance of this association through a meta-analysis.

METHODS

We conducted a systematic search of PubMed, MedLine, Scopus, and Web of Science databases using the keywords 'subclinical hypothyroidism and carotid intima-media thickness', from the beginning of each database until January 2023. We established the inclusion and exclusion criteria and considered studies that met the inclusion criteria. We used Jamovi for statistical analysis of the data.

RESULTS

We identified 39 observational studies that met the inclusion criteria, with 3430 subjects: 1545 SCH and 1885 EU. Compared to euthyroid subjects (EU), subjects with subclinical hypothyroidism (SCH) had significantly increased carotid intima-media thickness (CIMT) values; the estimated average mean difference was 0.08 (95% CI 0.05 to 0.10), p < 0.01, I2 = 93.82%. After the sensitivity analysis, a total of 19 from the 39 abovementioned studies were analyzed, with most studies showing a positive association between SCH and thickening of the carotid wall; the estimated average mean difference was 0.04 (95% CI 0.02 to 0.07), p = 0.03, I2 = 77.7. In addition, female sex, advanced age, and high cholesterol levels statistically significantly influenced this association.

CONCLUSIONS

Our meta-analysis indicates a significant positive association between SCH and increased CIMT, but with some limitations.

Thyroid Dysfunction and Atherosclerosis: A Systematic Review

BACKGROUND/AIM

Thyroid dysfunction, both hypo- and hyperthyroidism, has been associated with cardiovascular disease. The aim of this study was to evaluate the association between thyroid dysfunction and atherosclerosis measured mostly by carotid intima-media thickness, as well as discuss whether L-T4 replacement is able to reverse or slow down the progression of atherosclerosis.

MATERIALS AND METHODS

The review was conducted according the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. We performed on PubMed a literature search from May 2004 to January 2020, using the search terms 'subclinical hypothyroidism' or 'thyroid disorders' and 'carotid artery', 'carotid intima-media thickness (IMT)', 'levothyroxine', and 'atherosclerosis'.

RESULTS

Twenty-six studies were eligible and included in the analysis. Overall, the studies encompassed a total of 36.434 patients included in this review. Most studies indicated a proportional correlation between IMT and thyroid dysfunction. Levothyroxine (L-T4) replacement led to significant decrease of IMT after 1 year in most studies.

CONCLUSION

Most studies have concluded that thyroid dysfunction is associated with arterial wall remodeling and, thus, with increased cardiovascular risk. However, the exact mechanistic background of pathological structural changes in the arterial wall is still unsettled. Large randomized controlled studies are required to definitively address the extent to which T4 replacement therapy might benefit patients with subclinical thyroid disorders.

Effect of Thyroxin Treatment on Carotid Intima-Media Thickness (CIMT) Reduction in Patients with Subclinical Hypothyroidism (SCH): a Meta-Analysis of Clinical Trials

Aim: Research shows that subclinical hypothyroidism (SCH) is related to an increased carotid intima –media thickness (CIMT), a surrogate marker of subclinical cardiovascular disease (CVD). It is controversial whether or not SCH should be treated to reduce CVD morbidity and mortality. This meta-analysis aimed to determine whether SCH is associated with an increase in CIMT as compared to Euthyroidism (EU) and whether thyroxin (T4) treatment in SCH can reverse the change in CIMT.

Methods: Two independent reviewers conducted an extensive database research up to December 2016. A total of 12 clinical trials discussed the effect of Thyroxin on CIMT values at pre- and post-treatment in subjects with SCH.

Results: CIMT was significantly higher among SCH (n = 280) as compared to EU controls (n = 263) at baseline; the pooled weighted mean difference (WMD) of CIMT was 0.44 mm [95% confidence interval (CI) 0.14, 0.74], p = 0.004; I² = 65%. After treatment with thyroxin in subjects with SCH (n = 314), there was a statistically significant decrease in CIMT from pre- to post-treatment; the pooled WMD of CIMT decrease was [WMD −0.32; 95% CI (−0.47, −0.16), p = < 0.0001; I² = 2%], and it was no longer different from EU controls [WMD 0.13 mm; 95% CI (−0.04, 0.30); p = 0.14; I² = 27%]. The total cholesterol (TC), triglycerides (TG), and low-density lipoprotein (LDL) were higher in SCH as compared to EU controls and decreased significantly after treatment with thyroxin.

Conclusion: This meta-analysis shows that thyroxin therapy in subjects with SCH significantly decreases CIMT and improves lipid profile, modifiable CVD risk factors. Thyroid hormone replacement in subjects with SCH may play a role in slowing down or preventing the progression of atherosclerosis.

Aortic Intima-Media Thickness in Newborns with Congenital Hypothyroidism

BACKGROUND/AIMS

Congenital hypothyroidism (CH) in neonates is associated with lipid alterations that might be a risk factor for early cardiovascular disease in adult life. The aim of this study was to investigate the effect of CH on lipid metabolism and aortic intima media thickness (aIMT) as a unique finding of the increased risk of atherogenic risk in neonatal age.

METHODS

The study group consisted of 15 newborns with CH who were identified by neonatal mass screening (patient group), and 25 healthy newborns (control group). Serum lipid profiles and aIMT obtained from abdominal aorta were measured in all subjects.

RESULTS

The mean aIMT were higher in the patient group (0.46 ± 0.062 mm) compared with the control group (0.34 ± 0.035 mm; p = 0.006). The weight-adjusted aIMT of patients (0.13 ± 0.017 mm/kg) was also significantly greater than that of the controls (0.10 ± 0.019 mm/kg; p < 0.001). Total serum cholesterol levels were significantly higher in patients than those in healthy controls (130.80 ± 44.46 vs. 99.96 ± 18.87 mg/dl). The other lipid levels including triglyceride, low-density lipoprotein (LDL), high-density lipoprotein cholesterol and LDL cholesterol levels of the patients were slightly higher than those of the controls, without statistical significance.

CONCLUSION

Neonates with CH have significantly higher aIMT with lipid alterations. Hypothyroidism might increase the risk of early atherosclerosis even in the neonatal period.

Endothelial dysfunction in patients with subclinical hypothyroidism and the effects of treatment with levothyroxine

Background:

Subclinical hypothyroidism (SHT) may increase the risk of cardiovascular disease. We compared endothelial function between SHT patients and euthyroid individuals, and evaluated the effects of levothyroxine therapy on endothelial function in the patients.

Materials and Methods:

In a quasi-experimental study, flow-mediated dilatation (FMD) and intima-media thickness (IMT) were assessed in SHT patients and healthy controls (n = 25 in each group). Patients then received levothyroxine (50 μg/day) for 2 months, and the FMD and IMT assessments were repeated.

Results:

Patients and controls were similar in IMT (0.56 ± 0.09 vs. 0.58 ± 0.08 mm, P = 0.481), but FMD was lower in patients than in controls (4.95 ± 2.02 vs. 6.50 ± 2.57%, P = 0.011). A significant increase was observed in FMD (4.11 ± 2.37%, P = 0.001), but not in IMT (−0.004 ± 0.020 mm, P = 0.327), after levothyroxine therapy among the patients.

Conclusions:

Patients with SHT have endothelial dysfunction which responds to levothyroxine therapy. Randomized placebo-controlled trials are needed to confirm these findings.

Serum H-FABP levels in patients with hypothyroidism

OBJECTIVE

Hypothyroidism (HT) has an increased risk for cardiovascular mortality and morbidity due to increased atherosclerosis. Heart-type fatty acid binding protein (H-FABP) is abundant in the cytosol of cardiomyocytes, and transports fatty acids into these cells. Although H-FABP has been shown to increase in several atherosclerotic and inflammatory conditions, there is no literature data indicating an alteration in other atherosclerotic processes such as HT.

MATERIAL AND METHODS

A total of 39 patients with subclinical hypothyroidism (SCH), 26 patients with overt hypothyroidism (OH), and 29 healthy subjects were enrolled in this study. Carotid artery intima media thickness (CIMT) was measured by high resolution B mode ultrasonography. H-FABP levels, thyroid function test, and biochemical tests of all subjects were measured. The associations between H-FABP and thyroid test and CIMT were examined with correlation and regression analysis.

RESULTS

OH patients had higher H-FABP levels (mean, 6.18 ± 3.08 ng/mL) than both the SCH (mean, 3.81 ± 2.16 ng/mL) and the controls (mean, 2.12 ± 1.27 ng/mL) (P < 0.01 and < 0.001, respectively). SCH patients had increased serum H-FABP levels compared with control subjects (P < 0.01). CIMT of both OH and SCH patients was also significantly greater compared with control subjects (both of p < 0.01). H-FABP was significantly and positively correlated with age, systolic blood pressure, thyroid stimulating hormone (TSH) levels, and CIMT, and negatively correlated with fT4 levels. The H-FABP levels retained an independent and positive association with systolic blood pressure, and a negative association with fT4 levels.

CONCLUSION

Serum H-FABP levels progressively increased from the control group to the OH group. This suggests that H-FABP may be an indicator of low-level myocardial damage in HT, especially when used together with CIMT. Decreasing serum fT4 levels seem also to have an effect on H-FABP levels.

Right ventricular and right atrial function and deformation in patients with subclinical hypothyroidism: a two- and three-dimensional echocardiographic study

BACKGROUND

We sought to investigate right ventricular (RV) function and deformation assessed by three-dimensional echocardiography (3DE) and speckle tracking in patients with subclinical hypothyroidism (SHT), and to evaluate the influence of levothyroxine (L-T₄) therapy on RV remodeling.

METHODS

We included 50 untreated women with SHT and 45 healthy control women matched by age. The L-T₄ therapy was prescribed to all SHT patients who were followed 1 year after euthyroid status was achieved. All study participants underwent laboratory analyses which included thyroid hormone levels, and complete two-dimensional echocardiography (2DE) and 3DE examinations.

RESULTS

3DE RV end-diastolic volume and ejection fraction were significantly reduced in the SHT patients before therapy in comparison with the healthy controls and treated SHT subjects. RV longitudinal strain, systolic, and early diastolic strain rates (SRs) were significantly decreased, whereas RV late diastolic SR was increased in the SHT patients before therapy when comparing with the controls. 2DE speckle tracking imaging revealed that L-T₄ substitution therapy significantly improved RV systolic mechanics, whereas RV diastolic deformation was not completely recovered. Right atrial (RA) function and deformation were significantly impacted by SHT. Replacement L-T₄ treatment improved but did not completely restore RA mechanics in the SHT patients.

CONCLUSION

RV and RA function and mechanics are significantly affected by SHT. L-T₄ therapy and 1-year maintenance of euthyroid status improved but did not completely recover RV and RA function and deformation in the SHT patients, which implies that right heart remodeling caused by SHT is not reversible in a 1-year period.

Subclinical hypothyroidism: Controversies to consensus

Diagnoses of subclinicaal hypothyroidism (SCH) is biochemically made, when serum thyroid stimulating hormone (TSH) levels is elevated while free thyroid hormone levels are within normal reference range. SCH is diagnosed after excluding all other causes of elevated TSH levels. Symptoms of SCH may vary from being asymptomatic to having mild nonspecific symptoms. The risk of progression to overt hypothyroidism is related to number of factors including initial serum TSH concentration, presence of auto antibodies, family history and presence goiter. Various screening recommendations for thyroid function assessment are in practice. There are still controversies surrounding SCH and associated risk of various cardiovascular diseases (CVDs), pregnancy outcomes, neuropsychiatric issues, metabolic syndrome, and dyslipidemia. Consensus will require more large randomized clinical studies involving various age groups and medical condition, especially in developing countries. All these efforts will definitely improve our understanding of disease and ultimately patient outcomes.