Does subclinical hypothyroidism affect cardiac pump performance? Evidence from a magnetic resonance imaging study

Metabolic Syndrome, Thyroid Dysfunction, and Cardiovascular Risk: The Triptych of Evil

The triad formed by thyroid dysfunction, metabolic syndrome (MetS), and cardiovascular (CV) risk forms a network with many connections that aggravates health outcomes. Thyroid hormones (THs) play an important role in glucose and lipid metabolism and hemodynamic regulation at the molecular level. It is noteworthy that a bidirectional association between THs and MetS and their components likely exists as MetS leads to thyroid dysfunction, whereas thyroid alterations may cause a higher incidence of MetS. Thyroid dysfunction increases insulin resistance, the circulating levels of lipids, in particular LDL-C, VLDL-C, and triglycerides, and induces endothelial dysfunction. Furthermore, THs are important regulators of both white and brown adipose tissue. Moreover, the pathophysiological relationship between MetS and TH dysfunction is made even tighter considering that these conditions are usually associated with inflammatory activation and increased oxidative stress. Therefore, the role of THs takes place starting from the molecular level, then manifesting itself at the clinical level, through an increased risk of CV events in the general population as well as in patients with heart failure or acute myocardial infarction. Thus, MetS is frequently associated with thyroid dysfunction, which supports the need to assess thyroid function in this group, and when clinically indicated, to correct it to maintain euthyroidism. However, there are still several critical points to be further investigated both at the molecular and clinical level, in particular considering the need to treat subclinical dysthyroidism in MetS patients.

Sex difference in human diseases: mechanistic insights and clinical implications

Sex characteristics exhibit significant disparities in various human diseases, including prevalent cardiovascular diseases, cancers, metabolic disorders, autoimmune diseases, and neurodegenerative diseases. Risk profiles and pathological manifestations of these diseases exhibit notable variations between sexes. The underlying reasons for these sex disparities encompass multifactorial elements, such as physiology, genetics, and environment. Recent studies have shown that human body systems demonstrate sex-specific gene expression during critical developmental stages and gene editing processes. These genes, differentially expressed based on different sex, may be regulated by androgen or estrogen-responsive elements, thereby influencing the incidence and presentation of cardiovascular, oncological, metabolic, immune, and neurological diseases across sexes. However, despite the existence of sex differences in patients with human diseases, treatment guidelines predominantly rely on male data due to the underrepresentation of women in clinical trials. At present, there exists a substantial knowledge gap concerning sex-specific mechanisms and clinical treatments for diverse diseases. Therefore, this review aims to elucidate the advances of sex differences on human diseases by examining epidemiological factors, pathogenesis, and innovative progress of clinical treatments in accordance with the distinctive risk characteristics of each disease and provide a new theoretical and practical basis for further optimizing individualized treatment and improving patient prognosis.

Subclinical hypothyroidism predicts outcome in heart failure: insights from the T.O.S.CA. registry

Subclinical hypothyroidism (SH), defined as increased serum thyroid-stimulating hormone (TSH) with normal free T4 (fT4) levels, is frequently observed in the general population. Prevalence ranges from 0.6% to 1.8% in the adult population, depending on age, sex, and iodine intake. Several studies reported a worse prognosis in patients with heart failure with reduced ejection fraction (HFrEF) and SH, but they considered heterogeneous populations suffering mainly from severe SH. Aim of this study was to evaluate if SH was independently associated with the occurrence of cardiovascular death considering 30 months of follow-up. 277 HFrEF patients enrolled in the prospective, multicenter, observational T.O.S.CA. (Terapia Ormonale Scompenso CArdiaco) registry, were included in this analysis. Patients were divided into two groups according to the presence of SH (serum TSH levels > 4.5 mIU/L with normal fT4 levels). Data regarding clinical status, echocardiography, and survival were analyzed. Twenty-three patients displayed SH (87% mild vs 13% severe), while 254 were euthyroid. No differences were found in terms of age, sex, HF etiology, and left ventricular ejection fraction. When compared with the euthyroid group, SH patients showed higher TSH levels (7.7 ± 4.1 vs 1.6 ± 0.9, p < 0.001), as expected, with comparable levels of fT4 (1.3 ± 0.3 vs 1.3 ± 0.3, p = NS). When corrected for established predictors of poor outcome in HF, the presence of SH resulted to be an independent predictor of cardiovascular mortality (HR: 2.96; 5-95% CI:1.13-7.74; p = 0.03). Since thyroid tests are widely available and inexpensive, they should be performed in HF patients to detect subclinical disorders, evaluate replacement therapy, and improve prognosis.

Correlation of serum thyrotropin and thyroid hormone levels with diabetic kidney disease: a cross-sectional study

OBJECTIVE

The relationship between thyrotropin (TSH), free triiodothyronine (FT3), free thyroxine (FT4) and diabetic kidney disease (DKD) is still controversial, and this study analyzed the correlation between TSH, FT3, FT4 and DKD in patients with type 2 diabetes mellitus (T2DM).

METHODS

T2DM patients (1216) were divided into five groups based on serum TSH, FT3, and FT4 levels, differences in urinary albumin excretion rate (UACR), estimated glomerular filtration rate (eGFR) were compared. Binary logistic regression verified independent correlations among TSH, FT3, FT4 and UACR, eGFR. TSH and FT3 predictive values for DKD were analyzed using receiver operating characteristic (ROC) curves.

RESULTS

The prevalence of albuminuria with decreased eGFR was higher in T2DM patients with subclinical hypothyroidism and overt hypothyroidism than that in patients with normal thyroid function. TSH positively correlated with UACR (r = 0.133, p < 0.001) and positively correlated with eGFR (r = -0.218, p < 0.001), FT3 negatively correlated with UACR (r = -0.260, p < 0.001) and positively correlated with eGFR (r = 0.324, p < 0.001). With the change from the lower normal level to the increased level of TSH and the change from the higher normal level to the reduced level of FT3, the prevalence of albuminuria gradually increased, the prevalence of decreased eGFR gradually increased in TSH groups and FT3 groups. After adjusting for age, BMI, duration of diabetes, TPOAb, TGAb, smoking, drinking, hypertension, the use of anti-diabetic medications (metformin, sodium-glucose cotransporter 2 inhibitors), HbA1c, CRP, TC, TG, LDL-C, and HDL-C, both TSH and FT3 correlated with increased UACR (TSH: OR 1.253, p = 0.001; FT3: OR 0.166, p < 0.001) and decreased eGFR (TSH: OR 1.245, p < 0.001, FT3: OR 0.579, p < 0.001), but this correlation of TSH with eGFR < 60 mL/min/1.73 m2 was not found in male. The area under the ROC curve (AUC) for FT3 was greater than that for TSH (FT3: 0.64; TSH: 0.61).

CONCLUSIONS

Increased TSH and reduced FT3 levels were associated with DKD in T2DM patients, but in a sex-dependent manner. FT3 had a higher predictive value for DKD.

Changes of cardiac function: cardiac adaptation in patients with hypothyroidism assessed by cardiac magnetic resonance-a meta-analysis

Objective

The meta-analysis aimed to explore the cardiac adaptation in hypothyroidism patients by cardiac magnetic resonance.

Research methods and procedures

Databases including PubMed, Cochrane Library, Embase, CNKI, and Sinomed for clinical studies of hypothyroidism on cardiac function changes. Databases were searched from the earliest data to 15 June 2023. Two authors retrieved studies and evaluated their quality. Review Manager 5.4.1 and Stata18 were used to analyze the data. This study is registered with the International Platform of Registered Systematic Review and Meta-analysis Protocols (INPLASY), 202440114.

Results

Six studies were selected for further analysis. Five of them reported differences in cardiac function measures between patients with hypothyroidism and healthy controls, and three studies reported cardiac function parameters after treatment in patients with hypothyroidism. The fixed-effect model combined WMD values for left ventricular ejection fraction (LVEF) had a pooled effect size of -1.98 (95% CI -3.50 to -0.44], P=0.01), implying that LVEF was lower in patients with hypothyroidism than in healthy people. Analysis of heterogeneity found moderate heterogeneity (P = 0.08, I² = 50%). WMD values for stroke volume (SV), cardiac index (CI), left ventricular end-diastolic volume index(LVEDVI), left ventricular end-systolic volume (LESVI), and left ventricular mass index(LVMI) were also analyzed, and pooled effect sizes showed the CI and LVEDVI of patients with hypothyroidism ware significantly decrease (WMD=-0.47, 95% CI [-0.93 to -0.00], P=0.05, WMD=-7.99, 95%CI [-14.01 to -1.96], P=0.009, respectively). Patients with hypothyroidism tended to recover cardiac function after treatment [LVEF (WMD = 6.37, 95%CI [2.05, 10.69], P=0.004), SV (WMD = 7.67, 95%CI [1.61, 13.74], P=0.01), CI (WMD = 0.40, 95%CI [0.01, 0.79], P=0.05)], and there was no difference from the healthy controls.

Conclusion

Hypothyroidism could affect cardiac function, although this does not cause significant heart failure. It may be an adaptation of the heart to the hypothyroid state. There was a risk that this adaptation may turn into myocardial damage. Cardiac function could be restored after treatment in patients with hypothyroidism. Aggressive levothyroxine replacement therapy should be used to reverse cardiac function.

Systematic review registration

https://inplasy.com, identifier (INPLASY202440114).

Cardiovascular mechanisms of thyroid hormones and heart failure: Current knowledge and perspectives

A multiple hormonal imbalance that accompanies heart failure (HF) may have a significant impact on the clinical course in such patients. The non-thyroidal illness syndrome (NTIS), also referred to as euthyroid sick syndrome or low triiodothyronine syndrome, can be found in about 30% of patients with HF. NTIS represents a systemic adaptation to chronic illness that is associated with increased cardiac and overall mortality in patients with HF. While conclusions on thyroid-stimulating hormone, free triiodothyronine, total and free thyroxine are currently unresolved, serum total triiodothyronine levels and the ratio of free triiodothyronine to free thyroxine seem to provide the best correlates to the echocardiographic, laboratory and clinical parameters of disease severity. HF patients with either hyper- or hypothyroidism should be treated according to the appropriate guidelines, but the therapeutic approach to NTIS, with or without HF, is still a matter of debate. Possible treatment options include better individual titration of levothyroxine therapy, combined triiodothyronine plus thyroxine therapy and natural measures to increase triiodothyronine. Future research should further examine the cellular and tissue mechanisms of NTIS as well as new therapeutic avenues in patients with HF.

Estimation of left ventricular functions in patients with subclinical hypothyroidism: a meta-analysis

Objective

To evaluate left ventricular (LV) function in patients with subclinical hypothyroidism (ScH) compared to healthy individuals and to provide clinical hints for practitioners.

Methods

PubMed, Embase, Cochrane Library, and Web of Science were systematically searched in this meta-analysis. Studies evaluating LV function in ScH patients were included. Standardized mean difference (SMD) and the 95% confidence intervals (CIs) were calculated as effect size. Heterogeneity and risks of bias of included studies were assessed.

Results

A total of 9 studies were identified as eligible. The SMD for fractional shortening (FS, %) was -0.21 (95% CI: -0.60, 0.17; z = -1.08, p = 0.2788). The pooled SMD for systemic vascular resistance (SVR, dynes/sec·cm-5) was -0.41 (95% CI: -1.31, 0.49; z = -0.89, p = 0.3744). The pooled SMD for early diastolic mitral flow velocity/late diastolic mitral flow velocity (E/A) ratio was -0.74 (95% CI: -1.09, -0.39; z = -4.13, p < 0.001). The pooled SMD for ejection fraction (EF, %) was -0.35 (95% CI: -0.59, -0.12; z = -2.95, p = 0.0032).

Conclusion

ScH patients had significantly worse LV function parameters than healthy controls. These changes in LV function may be involved in the management of ScH.

Circulating thyroid hormones and clinical parameters of heart failure in men

Heart failure (HF) is a multiple hormonal deficiency syndrome which includes alterations in the serum concentration of thyroid hormones (TH). This cross-sectional study enrolled 215 male patients hospitalised for acute HF. Data on cardiovascular risk factors, chronic medications, cardiac function assessed by echocardiography, and clinical parameters of HF were prospectively collected. The independent predictive association of TH with all investigated parameters of the HF severity were assessed. The patient's mean age was 74.4 years, 57.2% had arterial hypertension, 54.0% were consuming alcohol, and 42.3% were diabetics. Multivariate analysis revealed that total triiodothyronine (TT3) was an independent predictor of greater left ventricular ejection fraction (LVEF; β = 0.223, p = 0.008), less progressed left ventricular diastolic dysfunction (LVDD; β = - 0.271, p = 0.001) and lower N-terminal pro-brain natriuretic peptide (NT-proBNP; β = - 0.365, p < 0.001). None of the TH other than TT3 was associated with LVDD or NT-proBNP, whereas free triiodothyronine (β = - 0.197, p = 0.004), free thyroxine (β = - 0.223, p = 0.001) and total thyroxine (β = - 0.140, p = 0.041) were inversely associated with LVEF. The present study suggests that, among TH, serum TT3 level is most closely associated with echocardiographic, laboratory and clinical parameters of the severity of HF in men.

The Role of Global Longitudinal Strain in Subclinical Hypothyroid Patients With Heart Failure

Introduction There is considerable evidence to suggest the role of thyroid hormone in acute coronary syndrome (ACS), but less is known about its prognostic role in heart failure (HF). We aimed to assess the role of global longitudinal strain (GLS) in patients hospitalized with HF and underlying subclinical hypothyroidism (SCHS). Methods A retrospective analysis of 161 subjects was conducted by dichotomizing them into HF with preserved ejection fraction (HFpEF) and HF with reduced ejection fraction (HFrEF) subgroups. SCHS was defined as a thyroid stimulating hormone level >4.50 mIU/L with a normal thyroxine level based on the evaluation of limits for lab markers from prior studies. HFpEF and HFrEF were defined as left ventricular ejection fraction (LVEF)>40% and LVEF≤40%, respectively, based on American College of Cardiology (ACC) guidelines. An abnormal speckled transthoracic echocardiographic (TTE) strain was defined as a left ventricular global longitudinal strain (LVGLS) value of >-15%. Results The mean age of the population was 62±8 years, and 55% were female. LVGLS was present in 121 patients with underlying SCHS (p<0.05). The patients with SCHS and abnormal LVGLS were found to have deranged left ventricular echocardiographic parameters (p<0.05). The derangements were greater for SCHS patients with HFrEF and abnormal LVGLS (p<0.05). Readmission rates at 30 days and in-hospital mortality were higher in SCHS patients with abnormal LVGLS (p<0.05). Conclusion The SCHS is associated with abnormal GLS in HF patients (either HFpEF or HFrEF) that results in remodeling and adverse outcomes, including mortality and readmission rates. Further studies are warranted to validate these findings in a larger population data pool.

The severity of valvular heart disease in euthyroid individuals is associated with thyroid hormone levels but not with TSH levels

Background

Abnormal thyroid function is a metabolic disorder and can lead to several complications, including cardiovascular diseases. In this study, we aimed to examine the relationship between clinical traits and outcomes and the thyroid hormone level of euthyroid individuals with valvular heart disease (VHD).

Method

The thyroid function was evaluated in 526 euthyroid VHD patients and 155 healthy control people. As well as clinical indicators were collected and analyzed.

Results

No difference in TSH levels (p>0.05) was recorded; however, fT3, TT3, and TT4 levels were lower in the euthyroid VHD patients than in healthy control(4.3 vs 4.63; 1.37 vs 1.48; 97.7 vs 102.09, respectively, all p<0.05), while the fT4 level was higher (12.91 vs 12.35, p<0.05). Moreover, all showed a continuous trend with the change of NYHA grade which does not consist of the incidence of euthyroid sick syndrome(ESS). Further analysis showed that for every 10-fold increase in BNP, fT4 increases by 83%, fT3 decreases by 30%, and TT3 decreases by 12% after being adjusted for other influencing factors. Meanwhile, adjusted fT4 was correlated with multiple worse clinical indicators, which were influenced by age.

Conclusion

Thyroid hormones are widely regulated in VHD patients even with acceptable cardiac function, except for TSH level. And the adjusted fT4 is related to worse clinical indicators and outcomes which are only recorded in patients under 53 years old.

The Impact of Hypothyroidism on Diabetes Mellitus and Its Complications: A Comprehensive Review

Diabetes mellitus (DM) is one of the most prevalent metabolic disorders in the world and is characterized by excessive blood glucose levels, which lead to deranged carbohydrate, protein, and lipid metabolisms. At its core, DM is an impairment of insulin metabolism, leading to a plethora of clinical features. The thyroid gland is another vital cog in the wheel of the endocrine system, and the hormones synthesized by it are heavily involved in the control of the body's metabolism. Hypothyroidism is a state in which thyroid hormones are deficient due to various factors and is characterized by a metabolically hypoactive state. Together, insulin, implicated in DM, and thyroid hormones engage in an intricate dance and serve to regulate the body's metabolism. It is imperative to explore the relationship between these two common endocrine disorders to understand their clinical association and mold treatments specific to patients in which they coexist. Both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) have been shown to have an increased association with hypothyroidism, especially in patients with risk factors including female sex, hyperlipidemia, obesity, and anemia. This review also explores DM's macrovascular and microvascular complications and their association with hypothyroidism. It is of great use to screen for hypothyroidism in diabetic patients. Specific protocols, especially for patients at an elevated risk, provide improved quality of life to patients affected by this highly prevalent disease.

Effect of Levothyroxine Supplementation on the Cardiac Morphology and Function in Patients With Subclinical Hypothyroidism: A Systematic Review and Meta-analysis

CONTEXT

The impact of abnormal thyroid hormone levels on the cardiovascular system has been explored for decades. Recent emerging evidence suggests that subclinical thyroid dysfunction, especially subclinical hypothyroidism (SCH), significantly affects cardiac indices.

OBJECTIVE

We aimed to determine whether levothyroxine (LT4), commonly used to treat hypothyroidism, affects cardiovascular indices in SCH patients.

METHODS

This is a systematic review and meta-analysis. We searched online databases for studies analyzing cardiac morphology and functional changes in SCH patients before and after LT4 supplementation. A total of 294 SCH patients participated and finished the follow-up. The standard mean difference and 95% CI were calculated in fixed or random-effects models. The clinical outcomes analyzed in this study included 18 indicators, mainly covering cardiac morphology, myocardial performance (including various indicators of systolic and diastolic function), mitral wave flow, and systemic vascular resistance.

RESULTS

A total of 11 studies met our search criteria. All studies explicitly mentioned that serum thyrotropin levels decreased to normal at follow-up. Our results suggest that the cardiac output (CO), left ventricular ejection fraction (LVEF), and the ratio of peak E velocity/peak A velocity were all significantly increased after LT4 supplementation compared with the baseline level. However, we found no clear evidence of significant morphological changes in the heart.

CONCLUSION

Judging from the obvious changes in the CO, LVEF, and E/A ratio, LT4 supplementation can effectively improve the cardiac systolic and diastolic dysfunction prevalent in SCH patients. This study provides evidence of the recommendation for LT4 supplementation in adult SCH patients.

Hypothyroidism and Risk of Cardiovascular Disease

Thyroid hormones (TH) have a significant impact on cellular oxidative metabolism. Besides that, they maintain vascular homeostasis by positive effects on endothelial and vascular smooth muscle cells. Subclinical (SCH) and clinical (CH) hypothyroidism influences target organs by changing their morphology and function and impaired blood and oxygen supply induced by accelerated atherosclerosis. The increased risk of acceleration and extension of atherosclerosis in patients with SCH and CH could be explained by dyslipidemia, diastolic hypertension, increased arterial stiffness, endothelial dysfunction, and altered blood coagulation. Instability of atherosclerotic plaque in hypothyroidism could cause excessive activity of the elements of innate immunity, which are characterized by: the significant presence of macrophages in atherosclerotic plaques, increased nuclear factor kappa B (NFkB) expression, and elevated levels of tumor necrosis factor α (TNF-α) and matrix metalloproteinase (MMP) 9, with reduced interstitial collagen, which all together creates inflammation milieu resulted in plaque rupture. Optimal substitution by levothyroxine (LT4) restores biochemical euthyroidism. In postmenopausal women and elderly patients with hypothyroidism and associated vascular comorbidity, excessive LT4 substitution could lead to atrial rhythm disorders and osteoporosis. Therefore, it is of interest to maintain thyroid-stimulating hormone (TSH) levels in the reference range, thus eliminating the deleterious effects of lower or higher TSH levels on the cardiovascular system. This review summarizes the recent literature on subclinical and clinical hypothyroidism and atherosclerotic cardiovascular disease and discusses the effects of LT4 replacement therapy on restoring biochemical euthyroidism and atherosclerosis processes.

Effect of hypothyroidism on contractile performance of isolated end-stage failing human myocardium

The relationship between hypothyroidism and the occurrence and progression of heart failure (HF) has had increased interest over the past years. The low T3 syndrome, a reduced T3 in the presence of normal thyroid stimulating hormone (TSH), and free T4 concentration, is a strong predictor of all-cause mortality in HF patients. Still, the impact of hypothyroidism on the contractile properties of failing human myocardium is unknown. Our study aimed to investigate that impact using ex-vivo assessment of force and kinetics of contraction/relaxation in left ventricular intact human myocardial muscle preparations. Trabeculae were dissected from non-failing (NF; n = 9), failing with no hypothyroidism (FNH; n = 9), and failing with hypothyroidism (FH; n = 9) hearts. Isolated muscle preparations were transferred into a custom-made setup where baseline conditions as well as the three main physiological modulators that regulate the contractile strength, length-dependent and frequency-dependent activation, as well as β-adrenergic stimulation, were assessed under near-physiological conditions. Hypothyroidism did not show any additional significant impact on the contractile properties different from the recognized alterations usually detected in such parameters in any end-stage failing heart without thyroid dysfunction. Clinical information for FH patients in our study revealed they were all receiving levothyroxine. Absence of any difference between failing hearts with or without hypothyroidism, may possibly be due to the profound effects of the advanced stage of heart failure that concealed any changes between the groups. Still, we cannot exclude the possibility of differences that may have been present at earlier stages. The effects of THs supplementation such as levothyroxine on contractile force and kinetic parameters of failing human myocardium require further investigation to explore its full potential in improving cardiovascular performance and cardiovascular outcomes of HF associated with hypothyroidism.

Atrioventricular Longitudinal Mechanics Using Novel Speckle-Tracking Improved Risk Stratification Beyond Baseline Thyroid Hormone in Asymptomatic Subclinical Hypothyroidism

BACKGROUND

Hypothyroidism is reportedly associated with increased cardiovascular risk and heart failure. We aimed to elucidate the mechanistic influence of atrio-ventricular deformations and their prognostic utilizations in asymptomatic subclinical hypothyroidism (SCH).

METHODS

We assessed speckle-tracking of deformations among 4173 population-based asymptomatic individuals classified as euthyroid (0.25< thyroid-stimulating hormone [TSH] ≤4.0 μIU/mL, n=3799) or having mild (4< TSH ≤10.0 μIU/mL, n=349) or marked (TSH >10 μIU/mL, n=25) SCH. We further related deformational indices to outcomes of atrial fibrillation and heart failure.

RESULTS

Despite borderline differences in indexed left ventricular mass and left atrial volume (P=0.054 and 0.051), those classified as mild and marked SCH presented with modest but significant reductions of global longitudinal strain, and showed elevated E/tissue Doppler imaging (TDI)-e', markedly diminished peak atrial longitudinal strain and higher left atrial stiffness (all P<0.05) when compared with euthyroid subjects. A higher TSH level was independently associated with reduced TDI-s'/TDI-e', worse global atrio-ventricular strains (global longitudinal strain/peak atrial longitudinal strain), elevated E/TDI-e', and worsened left atrial strain rate components (all P<0.05). Over a median 5.6 years (interquartile range, 4.7-6.5 years) follow-up, myocardial deformations yielded independent risk prediction using Cox regression in models adjusted for baseline covariates, N-terminal pro-brain natriuretic peptide, E/e', and treatment effect. Incorporation of global atrio-ventricular strain (global longitudinal strain/peak atrial longitudinal strain) and strain rates further showed improved risk reclassification when added to the baseline TSH strata (classified as euthyroid and mild and marked SCH; all P<0.05). Cox regression models remained significant with improved risk reclassification beyond TSH-based strata by using slightly different deformational cutoffs after excluding marked SCH group.

CONCLUSIONS

Hypothyroidism, even when asymptomatic, may widely influence subclinical atrio-ventricular mechanical functions that may lead to higher heart failure and atrial fibrillation risk. We proposed the potential usefulness and prognostic utilization of myocardial strains in such population.

Thyroid Hormone Plays an Important Role in Cardiac Function: From Bench to Bedside

Thyroid hormones (THs) are synthesized in the thyroid gland, and they circulate in the blood to regulate cells, tissues, and organs in the body. In particular, they exert several effects on the cardiovascular system. It is well known that THs raise the heart rate and cardiac contractility, improve the systolic and diastolic function of the heart, and decrease systemic vascular resistance. In the past 30 years, some researchers have studied the molecular pathways that mediate the role of TH in the cardiovascular system, to better understand its mechanisms of action. Two types of mechanisms, which are genomic and non-genomic pathways, underlie the effects of THs on cardiomyocytes. In this review, we summarize the current knowledge of the action of THs in the cardiac function, the clinical manifestation and parameters of their hemodynamics, and treatment principles for patients with hyperthyroid- or hypothyroid-associated heart disease. We also describe the cardiovascular drugs that induce thyroid dysfunction and explain the mechanism underlying the thyroid toxicity of amiodarone, which is considered the most effective antiarrhythmic agent. Finally, we discuss the recent reports on the involvement of thyroid hormones in the regulation of myocardial regeneration and metabolism in the adult heart.

The association of presystolic wave with subclinical left-ventricular dysfunction in patients with subclinical hypothyroidism

PURPOSE

Subclinical hypothyroidism (SCH) patients develop left-ventricular dysfunction (LVD) in an earlier stage. LVD could be detected with myocardial performance index (MPI), left -ventricular global longitudinal strain (LVGLS), and conventional and tissue-Doppler imaging (TDI). A presystolic wave (PSW) detected on late diastole is associated with LVD. We aimed to determine whether there is an association between PSW and subclinical LVD assessed by different echocardiographic methods in SCH patients.

METHODS

We prospectively enrolled 105 patients diagnosed with SCH in this study. Patients were divided into two groups based on the presence of PSW. Both groups were compared with respect to demographic, clinical, and echocardiographic properties. Multivariable regression analysis was performed to detect predictors of subclinical LVD.

RESULTS

The study included 70 PSW-positive patients (66%, mean age: 50.2) and 35 PSW-negative patients (34%, mean age: 46.5). PSW-positive patients had a lower platelet and a higher RDW level compared to PSW-negative patients. PSW-positive patients had more frequent subclinical LVD, which was assessed by MPI, by conventional and TDI parameters, and by LVGLS. PSW velocity was significantly correlated with MPI velocity (r = 0.31, p = 0.009), TSH level (r = 0.44, p < 0.001), and with LVGLS (r = 0.33, p = 0.005). The presence of PSW was an independent predictor of subclinical LVD in multivariable logistic regression analysis detected with MPI, LVGLS, and TDI parameters (OR = 5.409, p = 0.03; OR = 4.872, p = 0.005; OR = 5.632, p = 0.014, respectively).

CONCLUSION

PSW prevalence was 66% in SCH patients. PSW velocity was significantly correlated with MPI and LVGLS. The presence of PSW was independently associated with subclinical LVD in SCH patients.

Blood pressure characteristics of subclinical hypothyroidism: an observation study combined with office blood pressure and 24-h ambulatory blood pressure

OBJECTIVE

To investigate the characteristics of blood pressure in subclinical hypothyroidism by combining office blood pressure and 24-h ambulatory blood pressure.

METHODS

A total of 3078 adults voluntarily participants were enrolled in this study between December 2017 and November 2019. Among 1431 of them who did not fit exclusion criteria, 104 patients were with subclinical hypothyroidism (S-HYPO group), and 1327 were euthyroid participants (euthyroid group). Office blood pressure measurement and 24-h ambulatory blood pressure monitoring were carried out to analyze the characteristics of blood pressure in subclinical hypothyroidism.

RESULTS

There was no statistical difference in office SBP and DBP between the S-HYPO group and the euthyroid group (P > 0.05). On the ambulatory blood pressure level, the daytime SBP, night-time SBP, night-time SBP, 24-h SBP and DBP in the S-HYPO group were significantly higher than those in the euthyroid group (P = 0.048, P = 0.002, P = 0.003, P = 0. 014, P = 0. 046, respectively), and the proportion of nondipper blood pressure in the S-HYPO group was higher than that in the euthyroid group. Comprehensive analysis of blood pressure inside and outside the joint clinic revealed that the S-HYPO group was independently related to sustained hypertension and masked hypertension but not to white-coat hypertension (P = 0.004, P = 0.002, P = 0.886, respectively). After adjusting for age, sex, BMI, and other confounding factors, the above differences were still statistically significant (P < 0.05).

CONCLUSION

The characteristics of blood pressure in subclinical hypothyroidism can be more accurately understood by combining office blood pressure and ambulatory blood pressure.

Treatment of subclinical hypothyroidism: assessing when treatment is likely to be beneficial

Introduction: Subclinical hypothyroidism (SCH) is a common condition diagnosed in up to 16% of the population. SCH is diagnosed when serum TSH is high and circulating thyroid hormones are within the reference range. SCH is considered to be a mild form of thyroid failure by some due to the log-linear relationship between TSH and thyroid hormones. Nevertheless, it is unclear whether the treatment of SCH with thyroid hormones is beneficial, and hence, it is not surprising that expert opinions and recommendations from societies differ in their opinions on how best to manage SCH.Areas covered: This article reviews the currently available evidence pertaining to SCH and provides recommendations as to when treatment of SCH should be considered. An electronic search of PubMed from 1970 to 2019 was performed and systematically reviewed studies assessing the effects of treatment in SCH. The main areas that are considered are the effects of treatment on symptoms and quality of life, and important clinical consequences including psychocognitive outcomes and cardiovascular events.Expert opinion: Treatment of SCH with thyroid hormones is debated and the current literature in this area lacks clarity. We provide an evidence-based recommendation for when treatment of SCH with thyroid hormones should be considered.

Subclinical Thyroid Dysfunction and the Risk of Cardiovascular Disease

The prevalence of subclinical hypothyroidism (SH) is 3-10%. The prevalence of subclinical hyperthyroidism (SHr) is 0.7-9.7%. Thyroid hormones affect cardiac electrophysiology, contractility, and vasculature. SH is associated with an increased risk of coronary heart disease (CHD), especially in subjects under 65. SHr seems to be associated with a slightly increased risk of CHD and an increase in CHD-related mortality. Both SH and SHr carry an increased risk of developing heart failure (HF), especially in those under 65. Both SH and SHr are associated with worse prognoses in patients with existing HF. SH is probably not associated with atrial fibrillation (AF). SHr, low normal thyroid-stimulating hormone (TSH) and high normal free thyroxine (FT4) are all associated with the increased risk of AF. An association between endothelial dysfunction and SH seems to exist. Data regarding the influence of SHr on the peripheral vascular system are conflicting. SH is a risk factor for stroke in subjects under 65. SHr does not increase the risk of stroke. Both SH and SHr have an unfavourable effect on cardiovascular disease (CVD) and all-cause mortality. There is a U-shaped curve of mortality in relation to TSH concentrations. A major factor that modifies the relation between subclinical thyroid disease (SCTD) and mortality is age. SH increases blood pressure (BP). SHr has no significant effect on BP. Lipids are increased in patients with SH. In SHr, high-density lipoprotein cholesterol and lipoprotein( a) are increased. SCTD should be treated when TSH is over 10 mU/l or under 0.1 mU/l. Treatment indications are less clear when TSH is between normal limits and 0.1 or 10 mU/L. The current state of knowledge supports the understanding of SCTD's role as a risk factor for CVD development. Age is a significant confounding factor, probably due to age-associated changes in the TSH reference levels.

Outcomes of Cardiac Resynchronization Therapy in Patients with Hypothyroidism and Heart Failure

Background

Hypothyroidism is known to be associated with adverse clinical outcomes in heart failure. The association between hypothyroidism and cardiac resynchronization therapy outcomes in patients with severe heart failure is not clear.

Methods

The study included 1316 patients who received cardiac resynchronization therapy between 2002 and 2015. Baseline demographics and cardiac resynchronization therapy outcomes, including left ventricular ejection fraction, New York Heart Association class, appropriate implantable cardioverter-defibrillator therapy, and all-cause mortality, were collected from the electronic health record.

Results

Of the study cohort, 350 patients (26.6%) were classified as the hypothyroidism group. The median duration of follow-up was 3.6 years (interquartile range, 1.7–6.2 years). Hypothyroidism was not associated with a higher risk of all-cause mortality in patients receiving CRT for heart failure. The risk of appropriate implantable cardioverter-defibrillator therapy significantly increased in association with increased baseline thyroid-stimulating hormone level in the entire cohort (hazard ratio, 1.23 per 5mIU/L increase; 95% CI, 1.01–1.5; P = 0.04) as well as in the hypothyroid group (hazard ratio, 1.44 per 5mIU/L increase; 95% CI, 1.13–1.84; P = 0.004).

Conclusions

CRT improves cardiac function in hypothyroid patients. The ventricular arrhythmic events requiring ICD therapies are associated with baseline TSH level, which might be considered as an important biomarker to stratify the risk of sudden death for patients with heart failure and hypothyroidism.

Novel noninvasive estimation of mixed venous oxygen saturation by echocardiography and expired gas analysis

Mixed venous oxygen (O₂) saturation ([Formula: see text]) is an important measure for evaluating the sufficiency of cardiac output (CO) relative to whole body O₂ consumption (V̇o₂), while clinical use is limited to the required invasive catheterization. According to Fick's equation, V̇o₂ (mL/min) = CO (L/min) × Hb (g/dL) × 1.36 (mL/g) × ([Formula: see text] - [Formula: see text])/10 (Hb = hemoglobin concentration, [Formula: see text] = arterial blood O₂ saturation). Because V̇o₂, CO, Hb, and [Formula: see text] can be measured noninvasively with expired gas analysis, echocardiography, a simple blood test, and percutaneous O₂ saturation, respectively, [Formula: see text] can be calculated noninvasively. We hypothesized that noninvasively calculated [Formula: see text] shows a significant correlation and agrees well with invasively measured [Formula: see text]. In 47 patients (29 men; mean age, 70 ± 12 yr) who underwent right heart catheterization, [Formula: see text] was directly measured by sampling pulmonary artery blood. Noninvasively calculated [Formula: see text] was also obtained by the method described above. The calculated [Formula: see text] was significantly correlated with the measured [Formula: see text] (r = 0.79, P < 0.001) and was significantly smaller than the measured [Formula: see text] (70 ± 5.1 vs. 72.1 ± 4.9%, P < 0.001). Bias at [Formula: see text] was -2.2% (95% confidence interval, -3.2 to -1.1%) with limits of agreement from -9.5 to 5.2%, demonstrating acceptable agreement. The optimal cutoff value of calculated [Formula: see text] was 69% for reduced measured [Formula: see text] < 70% with an area under the curve of 0.94. Reduced calculated [Formula: see text] < 69% indicated a sensitivity of 92.9% and a specificity of 90.9% for reduced measured [Formula: see text] < 70%. Noninvasive [Formula: see text] calculated from echocardiography, expired gas analysis, percutaneous arterial blood O₂ saturation, and hemoglobin level significantly correlated and agreed well with direct [Formula: see text] measured by catheterization. This novel method allows for practical evaluation of [Formula: see text] to assess the sufficiency of CO according to whole body metabolism.NEW & NOTEWORTHY Clinical use of mixed venous oxygen saturation ([Formula: see text]) is limited to the required invasive procedure. With Fick's equation, expired gas analysis, echocardiography, simple blood tests, and percutaneous oxygen saturation, [Formula: see text] can be calculated noninvasively. We hypothesized that noninvasively calculated [Formula: see text] shows a significant correlation and agrees well with invasively measured [Formula: see text]. The present study examined the relationship between measured [Formula: see text] and calculated [Formula: see text] in patients who underwent right heart catheterization and demonstrated acceptable agreement. This novel method can expand the indication of evaluating [Formula: see text].

Relationship of thyroid dysfunction with cardiovascular diseases: updated review on heart failure progression

Heart disease remains the leading cause of death globally. Heart failure (HF) is a clinical syndrome that results from impairment of the ability of the ventricle to fill with or eject blood. Over the past two decades, accumulated evidence has revealed the contribution of thyroid hormones to cardiovascular (CV) events, exerting their action through genomic and non-genomic pathways within the cardiomyocytes. The pivotal role of thyroid hormones in maintaining cardiac homeostasis has been observed in previous investigations which suggest that the CV system is adversely impacted by fluctuations in thyroid hormone levels, such as those that occur in hypothyroidism, hyperthyroidism, and low triiodothyronine syndrome (LT₃S). Thyroid dysfunction has direct effects on myocardial contractility, systolic and diastolic blood pressure, heart mass, heart rate, ejection fraction, and heart output, which may ultimately lead to HF. Recent clinical data have shown that thyroid hormone replacement therapy for hypothyroid patients appears to provide the potential for reducing CV events. Therefore, this review aims to address the impact of thyroid hormone dysfunction on pathophysiological mechanisms contributing to the development and progression of HF.

Effect of Levothyroxine on Left Ventricular Ejection Fraction in Patients With Subclinical Hypothyroidism and Acute Myocardial Infarction: A Randomized Clinical Trial

IMPORTANCE

Thyroid hormones play a key role in modulating myocardial contractility. Subclinical hypothyroidism in patients with acute myocardial infarction is associated with poor prognosis.

OBJECTIVE

To evaluate the effect of levothyroxine treatment on left ventricular function in patients with acute myocardial infarction and subclinical hypothyroidism.

DESIGN, SETTING, AND PARTICIPANTS

A double-blind, randomized clinical trial conducted in 6 hospitals in the United Kingdom. Patients with acute myocardial infarction including ST-segment elevation and non-ST-segment elevation were recruited between February 2015 and December 2016, with the last participant being followed up in December 2017.

INTERVENTIONS

Levothyroxine treatment (n = 46) commencing at 25 µg titrated to aim for serum thyrotropin levels between 0.4 and 2.5 mU/L or identical placebo (n = 49), both provided in capsule form, once daily for 52 weeks.

MAIN OUTCOMES AND MEASURES

The primary outcome measure was left ventricular ejection fraction at 52 weeks, assessed by magnetic resonance imaging, adjusted for age, sex, type of acute myocardial infarction, affected coronary artery territory, and baseline left ventricular ejection fraction. Secondary measures were left ventricular volumes, infarct size (assessed in a subgroup [n = 60]), adverse events, and patient-reported outcome measures of health status, health-related quality of life, and depression.

RESULTS

Among the 95 participants randomized, the mean (SD) age was 63.5 (9.5) years, 72 (76.6%) were men, and 65 (69.1%) had ST-segment elevation myocardial infarction. The median serum thyrotropin level was 5.7 mU/L (interquartile range, 4.8-7.3 mU/L) and the mean (SD) free thyroxine level was 1.14 (0.16) ng/dL. The primary outcome measurements at 52 weeks were available in 85 patients (89.5%). The mean left ventricular ejection fraction at baseline and at 52 weeks was 51.3% and 53.8%, respectively, in the levothyroxine group compared with 54.0% and 56.1%, respectively, in the placebo group (adjusted difference in groups, 0.76% [95% CI, -0.93% to 2.46%]; P = .37). None of the 6 secondary outcomes showed a significant difference between the levothyroxine and placebo treatment groups. There were 15 (33.3%) and 18 (36.7%) cardiovascular adverse events in the levothyroxine and placebo groups, respectively.

CONCLUSIONS AND RELEVANCE

In this preliminary study involving patients with subclinical hypothyroidism and acute myocardial infarction, treatment with levothyroxine, compared with placebo, did not significantly improve left ventricular ejection fraction after 52 weeks. These findings do not support treatment of subclinical hypothyroidism in patients with acute myocardial infarction.

TRIAL REGISTRATION

isrctn.org Identifier: http://www.isrctn.com/ISRCTN52505169.

The Impact of Levothyroxine on Cardiac Function in Older Adults With Mild Subclinical Hypothyroidism: A Randomized Clinical Trial

BACKGROUND

Subclinical hypothyroidism has been associated with heart failure, but only small trials assessed whether treatment with levothyroxine has an impact on cardiac function.

METHODS

In a randomized, double-blind, placebo-controlled, trial nested within the TRUST trial, Swiss participants ages ≥65 years with subclinical hypothyroidism (thyroid-stimulating hormone [TSH] 4.60-19.99 mIU/L; free thyroxine level within reference range) were randomized to levothyroxine (starting dose of 50 µg daily) to achieve TSH normalization or placebo. The primary outcomes were the left ventricular ejection fraction for systolic function and the ratio between mitral peak velocity of early filling to early diastolic mitral annular velocity (E/e' ratio) for diastolic function. Secondary outcomes included e' lateral/septal, left atrial volume index, and systolic pulmonary artery pressure.

RESULTS

A total of 185 participants (mean age 74.1 years, 47% women) underwent echocardiography at the end of the trial. After a median treatment duration of 18.4 months, the mean TSH decreased from 6.35 mIU/L to 3.55 mIU/L with levothyroxine (n = 96), and it remained elevated at 5.29 mIU/L with placebo (n = 89). The adjusted between-group difference was not significant for the mean left ventricular ejection fraction (62.7% vs 62.5%, difference = 0.4%, 95% confidence interval -1.8% to 2.5%, P = 0.72) and the E/e' ratio (10.6 vs 10.1, difference 0.4, 95% confidence interval -0.7 to 1.4, P = 0.47). No differences were found for the secondary diastolic function parameters or for interaction according to sex, baseline TSH, preexisting heart failure, and treatment duration (P value >0.05).

CONCLUSION

Systolic and diastolic heart function did not differ after treatment with levothyroxine compared with placebo in older adults with mild subclinical hypothyroidism.

Regulation of nitric oxide production in hypothyroidism

Hypothyroidism is a common endocrine disorder that predominantly occurs in females. It is associated with an increased risk of cardiovascular diseases (CVD), but the molecular mechanism is not known. Disturbance in lipid metabolism, the regulation of oxidative stress, and inflammation characterize the progression of subclinical hypothyroidism. The initiation and progression of endothelial dysfunction also exhibit these changes, which is the initial step in developing CVD. Animal and human studies highlight the critical role of nitric oxide (NO) as a reliable biomarker for cardiovascular risk in subclinical and clinical hypothyroidism. In this review, we summarize the recent literature findings associated with NO production by the thyroid hormones in both physiological and pathophysiological conditions. We also discuss the levothyroxine treatment effect on serum NO levels in hypothyroid patients.

Serum nitric oxide levels correlate with quality of life questionnaires scores of hypothyroid females

Primary hypothyroidism can affect lipid metabolism, cardiovascular (CV) function, and overall patients' quality of life (QoL). Decrease in serum nitric oxide (NO) levels could promote the atherosclerosis acceleration in hypothyroid patients. Our hypothesis is that serum NO level is altered in hypothyroidism; more specifically, we hypothesize that the early vascular changes that can be observed in hypothyroidism could be due to these alterations and that serum NO levels are associated with lipid levels in female patients diagnosed with subclinical hypothyroidism (SCH) or clinical hypothyroidism (CH). Furthermore, since serum NO level is an early marker of atherosclerosis and related CV disorders, which are commonly present and follow hypothyreosis and greatly contribute to overall QoL, we further hypothesized that NO level would correlate with Thyroid Symptom Questionnaire (TSQ) and General Health Questionnaire 12 (GHQ12) scores in hypothyroid patients. A collaterally of our hypothesis was that levothyroxine (LT4) treatment would affect serum NO levels as well as TSQ and GHQ12 scores. Therefore, we have analyzed lipid profile, the level of NO and QoL scores in female patients diagnosed with SCH and CH in order to determine the correlation between NO and generic and thyroid disease symptoms in treatment naïve SCH and CH patients and after LT4 treatment and laboratory euthyroidism achievement. As a consequence of our hypothesis is that measurement of serum NO level in SCH and CH patients may be an innovative way to improve LT4 treatment efficacy. This assumption could have a practical significance for future investigations regarding the management of hypothyroidism treatment protocols in current guidelines.

Thyroid Hormones and Cardiovascular Function and Diseases

Thyroid hormone (TH) receptors are present in the myocardium and vascular tissue, and minor alterations in TH concentration can affect cardiovascular (CV) physiology. The potential mechanisms that link CV disease with thyroid dysfunction are endothelial dysfunction, changes in blood pressure, myocardial systolic and diastolic dysfunction, and dyslipidemia. In addition, cardiac disease itself may lead to alterations in TH concentrations (notably, low triiodothyronine syndrome) that are associated with higher morbidity and mortality. Experimental data and small clinical trials have suggested a beneficial role of TH in ameliorating CV disease. The aim of this review is to provide clinicians dealing with CV conditions with an overview of the current knowledge of TH perturbations in CV disease.

Evaluation of left atrial volume and functions by real time three-dimensional echocardiography in patients with subclinical hypothyroidism before and after levothyroxine therapy

BACKGROUND/AIMS

The cardiovascular system is one of the major targets of thyroid hormones. Subclinical hypothyroidism (SCH) is a common disease that can represent "early" thyroid failure. Our aim was to evaluate left atrial (LA) volume and functions in patients with SCH using real time three-dimensional echocardiography (RT3DE) and also to investigate changes in LA parameters after the levothyroxine treatment.

METHODS

In total, 44 patients with SCH and 40 age- and gender-matched controls were studied. Assessments included history, physical examination and echocardiography. All patients with SCH were followed up with replacement therapy until the euthyroid status was achieved.

RESULTS

In patients with SCH, LA total emptying volume, passive emptying volume, and passive ejection fraction were significantly reduced while LA minimal volume, active emptying volume, and active emptying fraction were significantly increased than in control group. Following the levothyroxine treatment, LA volume and function parameters were observed to be significantly improved. A negative correlation between the change of thyroid stimulating hormone (TSH) and change of LA active emptying volume and a positive correlation between the change of TSH level and change of LA passive emptying volume were found.

CONCLUSION

It was shown that volume and functions of LA were impaired in patients with SCH. However, impaired parameters were improved after the levothyroxine treatment. These findings may be indicative of subclinical heart involvement that could lead to functional and structural changes in patients with SCH.

The Management of Thyroid Abnormalities in Chronic Heart Failure

The cardiovascular system is one of the main targets of thyroid hormone action, and triiodothyronine deficiency has crucial consequences on cardiac structure and function. Patients with overt or subclinical hypothyroidism should be treated with levothyroxine to improve their cardiovascular function and the potential risk of heart failure. Even patients with thyroid hormone deficiency and heart failure should receive replacement doses of levothyroxine to improve their prognosis and worsening of the cardiovascular function. An innovative therapeutic multifactorial approach could improve the progression of heart failure. There is a potential beneficial effect of thyroid hormones and their analogs in patients with heart failure.

Subclinical thyroid dysfunction is associated with adverse prognosis in heart failure patients with reduced ejection fraction

BACKGROUND

Subclinical thyroid dysfunction whose typical patterns include subclinical hypothyroidism and subclinical hyperthyroidism, has been indicated to be associated with an increased risk of heart failure (HF). However, the relationship between subclinical thyroid dysfunction and the clinical outcomes of HF patients is uncertain. This meta-analysis was conducted to assess the association between subclinical thyroid dysfunction and the clinical outcomes of HF patients.

METHODS

Pubmed, Embase, Web of Science and Cochrane Central Register of Clinical Trials were searched for eligible studies published up to August 1, 2018 which reported the association between subclinical thyroid dysfunction and the clinical outcomes of HF patients. The pooled hazard ratio (HR) with the corresponding 95% confidence interval (CI) was used to assess the association.

RESULTS

Fourteen studies met the eligibility criteria and a total of 21,221 patients with heart failure were included in the meta-analysis. Compared with HF patients with euthyroidism, the pooled HR of subclinical hypothyroidism for all-cause mortality was 1.45 (95% CI 1.26-1.67) in a randomized effects model with mild heterogeneity (I² = 40.1, P = 0.073). The pooled HR of subclinical hypothyroidism for cardiac death and/or hospitalization was 1.33 (1.17-1.50) in a randomized effects model with moderate heterogeneity (I² = 69.4, P < 0.001). Subclinical hyperthyroid can increase the risk of all-cause mortality without heterogeneity (HR 1.31, 95% CI 1.10-1.55, I² = 25.5%, P = 0.225) but have no influence on the risk of cardiac death and/or hospitalization (HR 1.03, 95% CI 0.87-1.23, I² = 0.0%, P = 0.958). These significant adverse associations were also retained in subgroup analysis. Sensitivity analysis demonstrated the stability of the results of our meta-analysis.

CONCLUSIONS

Both subclinical hypothyroidism and subclinical hyperthyroidism are associated with adverse prognosis in patients with HF. Subclinical thyroid dysfunction may be a useful and promising predictor for the long-term prognosis in HF patients.

Cardiovascular Implications of Diabetes, Metabolic Syndrome, Thyroid Disease, and Cardio-Oncology in Women

Cardiovascular disease may be associated with several comorbidities, including diabetes mellitus, thyroid disorders, and the metabolic syndrome, which are predominantly observed in women and often starting at particular ages. In addition, common treatment options for carcinomas frequently seen in women may induce serious cardiotoxic effects. We review the scope of the problem, the pathophysiologic mechanisms involved, as well as the resulting abnormalities regarding cardiac structure and function as observed by using imaging techniques.

Thyroid Function in Patients with Type 2 Diabetes Mellitus and Diabetic Nephropathy: A Single Center Study

Background

Diabetes mellitus is a common metabolic disease and the prevalence is increasing rapidly. Thyroid disorders including subclinical hypothyroidism (SCH) and low triiodothyronine (T3) syndrome are frequently observed in diabetic patients. We conducted a study to explore thyroid function in patients with type 2 diabetes mellitus (T2DM) and diabetic nephropathy (DN).

Methods

We included 103 healthy volunteers, 100 T2DM patients without DN, and 139 with DN. Physical examinations including body mass index and blood pressure and laboratory measurements including renal function, thyroid function, and glycosylated hemoglobin were conducted.

Results

Patients with DN had higher thyroid stimulating hormone (TSH) levels and lower free T3 (FT3) levels than those without DN (p < 0.01). The prevalence of SCH and low FT3 syndrome in patients with DN was 10.8% and 20.9%, respectively, higher than that of controls and patients without DN (p < 0.05). Through Pearson correlation or Spearman rank correlation analysis, in patients with DN, there were positive correlations in TSH with serum creatinine (r = 0.363, p = 0.013) and urinary albumin-to-creatinine ratio (r = 0.337, p = 0.004), and in FT3 with estimated glomerular filtration rate (eGFR) with statistical significance (r = 0.560, p < 0.001).

Conclusions

High level of TSH and low level of FT3 were observed in T2DM patients with DN. Routine monitoring of thyroid function in patients with DN is necessary, and management of thyroid dysfunction may be a potential therapeutic strategy of DN.

Cardioprotection and Thyroid Hormones in the Clinical Setting of Heart Failure

Ischemic heart disease is the main cause of morbidity and mortality worldwide and is becoming more widespread with population aging. Cardioprotection is a dynamic process characterized by mechanisms related to myocardial damage and activation of protective factors. Targeting these processes could be attractive as a new therapeutic strategy in the evolution of post-ischemic heart failure (HF). In this context, the role of thyroid hormone (TH)-mediated cardioprotection is supported by a number of findings regarding the modulation of neuroendocrine systems, inflammatory and oxidative stress status, pro-survival intracellular pathways, and epigenetic factors, its effects on cardiac angiogenesis, structure, and function and on the preservation of mitochondrial function and morphology, and its beneficial effects on cell growth and redifferentiation. Moreover, the numerous effects of TH on the heart involve genomic mechanisms, which include cardiac differentiation during the perinatal period and non-genomic action, directed toward the maintenance of cardiovascular homeostasis. This evidence suggests that there is an opportunity to treat HF patients with TH. This review is mainly focused on the clinical evidence of the role of the thyroid system in the complex setting of HF.

Levels of serum thyroxine, triidothyronine and thyrotropin in patients with acute myocardial infarction

Objective

To determine the levels of serum thyroxine (T3, T4), triiodothyronine and thyrotropin in patients with acute myocardial infarction (AMI).

Methods

It was an observational prospective study and 60 patients (both males and females) of AMI, (diagnosed by ECG & cardiac enzymes.) were included. Serum thyroid stimulating hormone (TSH), Free T3 and Free T4 were measured and relevant data was entered into a predesigned proforma.

Results

FT3 levels were below the reference range in 56.7% cases while both the FT4 and TSH values were found to be the lower limit of normal range. When the decrease in FT3 was correlated with the duration of illness, it was found that significant inverse correlation existed between FT3 value and the duration of illness and linear regression line was obtained. No such correlation existed between FT4 and TSH values.

Conclusion

Thyroid hormone levels (FT3) decreases in AMI and this change is associated with the duration of illness.

Subclinical hypothyroidism and the development of heart failure: an overview of risk and effects on cardiac function

The prevalence of subclinical hypothyroidism (SCH) ranges from 5 to 15% of the general population. However, it remains controversial if SCH warrants life-long thyroxine replacement therapy. Patients with a thyroid-stimulating hormone (TSH) level > 10 mIU/L have a higher risk of developing heart failure with reduced ejection fraction as compared to subjects with normal thyroid function. However, abnormally high TSH levels could also be connected with an overall lower metabolic rate and better survival in elderly subjects. The potential mechanisms responsible for diastolic dysfunction of the left ventricle (LV) in SCH are connected with endothelial dysfunction and arterial stiffness, inflammatory state and are driven by TSH apoptosis-derived microparticles. The impact of SCH on LV systolic function is more controversial, and it is connected not only with cardiac remodelling but also with predisposition of patients with SCH to the conditions leading to heart failure. This review presents an overview of processes in the context of potential benefits of thyroxine supplementation therapy.

MANAGEMENT OF ENDOCRINE DISEASE: Pitfalls on the replacement therapy for primary and central hypothyroidism in adults

Hypothyroidism is one of the most common hormone deficiencies in adults. Most of the cases, particularly those of overt hypothyroidism, are easily diagnosed and managed, with excellent outcomes if treated adequately. However, minor alterations of thyroid function determine nonspecific manifestations. Primary hypothyroidism due to chronic autoimmune thyroiditis is largely the most common cause of thyroid hormone deficiency. Central hypothyroidism is a rare and heterogeneous disorder characterized by decreased thyroid hormone secretion by an otherwise normal thyroid gland, due to lack of TSH. The standard treatment of primary and central hypothyroidism is hormone replacement therapy with levothyroxine sodium (LT4). Treatment guidelines of hypothyroidism recommend monotherapy with LT4 due to its efficacy, long-term experience, favorable side effect profile, ease of administration, good intestinal absorption, long serum half-life and low cost. Despite being easily treatable with a daily dose of LT4, many patients remain hypothyroid due to malabsorption syndromes, autoimmune gastritis, pancreatic and liver disorders, drug interactions, polymorphisms in DIO2 (iodothyronine deiodinase 2), high fiber diet, and more frequently, non-compliance to LT4 therapy. Compliance to levothyroxine treatment in hypothyroidism is compromised by daily and fasting schedule. Many adult patients remain hypothyroid due to all the above mentioned and many attempts to improve levothyroxine therapy compliance and absorption have been made.

Cardiotoxicity with vascular endothelial growth factor inhibitor therapy

Angiogenesis inhibitors targeting the vascular endothelial growth factor (VEGF) signaling pathway (VSP) have been important additions in the therapy of various cancers, especially renal cell carcinoma and colorectal cancer. Bevazicumab, the first VSP to receive FDA approval in 2004 targeting all circulating isoforms of VEGF-A, has become one of the best-selling drugs of all times. The second wave of tyrosine kinase inhibitors (TKIs), which target the intracellular site of VEGF receptor kinases, began with the approval of sorafenib in 2005 and sunitinib in 2006. Heart failure was subsequently noted, in 2-4% of patients on bevacizumab and in 3-8% of patients on VSP-TKIs. The very fact that the single-targeted monoclonal antibody bevacizumab can induce cardiotoxicity supports a pathomechanistic role for the VSP and the postulate of the "vascular" nature of VSP inhibitor cardiotoxicity. In this review we will outline this scenario in greater detail, reflecting on hypertension and coronary artery disease as risk factors for VSP inhibitor cardiotoxicity, but also similarities with peripartum and diabetic cardiomyopathy. This leads to the concept that any preexisting or coexisting condition that reduces the vascular reserve or utilizes the vascular reserve for compensatory purposes may pose a risk factor for cardiotoxicity with VSP inhibitors. These conditions need to be carefully considered in cancer patients who are to undergo VSP inhibitor therapy. Such vigilance is not to exclude patients from such prognostically extremely important therapy but to understand the continuum and to recognize and react to any cardiotoxicity dynamics early on for superior overall outcomes.

Diffuse Myocardial Injuries are Present in Subclinical Hypothyroidism: A Clinical Study Using Myocardial T1-mapping Quantification

Subclinical hypothyroidism (SHT) is a common disorder that may represent early thyroid dysfunction and is related to adverse cardiovascular events. However, myocardial injuries induced by SHT are difficult to detect. Our previous study demonstrated that the cardiac magnetic resonance (CMR) myocardial longitudinal relaxation time (T1) mapping technique is a useful tool for assessing diffuse myocardial injuries in overt hypothyroidism patients. This study was designed to detect whether diffuse myocardial injuries were present in SHT by using the T1 mapping technique. We found that SHT participants had significantly increased native T1 values within four segments of the left ventricle (all p < 0.01), especially patients with thyroid-stimulating hormone (TSH) levels ≥10 µIU/mL, compared with those in the controls. In addition, the native T1 values were negatively correlated with free thyroxine (FT4) (r = −0.476, p = 0.003) and were positively correlated with TSH (r = 0.489, p = 0.002). Furthermore, left ventricular diastolic function estimated by the peak filling rate (PFR) was significantly lower in patients with TSH levels ≥10 µIU/mL than that in the controls (p < 0.05). In conclusion, diffuse myocardial injuries were present in SHT, and T1 mapping may be a useful tool for evaluating mild myocardial injuries in SHT at an early stage. Our study is the first to confirm myocardial injuries in SHT patients using T1 mapping.

Myocardium of patients with dilated cardiomyopathy presents altered expression of genes involved in thyroid hormone biosynthesis

Background

The association between dilated cardiomyopathy (DCM) and low thyroid hormone (TH) levels has been previously described. In these patients abnormal thyroid function is significantly related to impaired left ventricular (LV) function and increased risk of death. Although TH was originally thought to be produced exclusively by the thyroid gland, we recently reported TH biosynthesis in the human ischemic heart.

Objectives

Based on these findings, we evaluated whether the genes required for TH production are also altered in patients with DCM.

Methods

Twenty-three LV tissue samples were obtained from patients with DCM (n = 13) undergoing heart transplantation and control donors (n = 10), and used for RNA sequencing analysis. The number of LV DCM samples was increased to 23 to determine total T4 and T3 tissue levels by ELISA.

Results

We found that all components of TH biosynthesis are expressed in human dilated heart tissue. Expression of genes encoding thyroperoxidase (–2.57-fold, P < 0.05) and dual oxidase 2 (2.64-fold, P < 0.01), the main enzymatic system of TH production, was significantly altered in patients with DCM and significantly associated with LV remodeling parameters. Thyroxine (T4) cardiac tissue levels were significantly increased (P < 0.01), whilst triiodothyronine (T3) levels were significantly diminished (P < 0.05) in the patients.

Conclusions

Expression of TH biosynthesis machinery in the heart and total tissue levels of T4 and T3, are altered in patients with DCM. Given the relevance of TH in cardiac pathology, our results provide a basis for new gene-based therapeutic strategies for treating DCM.

Cardiac ischemia/reperfusion injury is inversely affected by thyroid hormones excess or deficiency in male Wistar rats

AIM

Thyroid dysfunctions can increase the risk of myocardial ischemia and infarction. However, the repercussions on cardiac ischemia/reperfusion (IR) injury remain unclear so far. We report here the effects of hypothyroidism and thyrotoxicosis in the susceptibility to IR injury in isolated rat hearts compared to euthyroid condition and the potential role of antioxidant enzymes.

METHODS

Hypothyroidism and thyrotoxicosis were induced by administration of methimazole (MMZ, 300 mg/L) and thyroxine (T4, 12 mg/L), respectively in drinking water for 35 days. Isolated hearts were submitted to IR and evaluated for mechanical dysfunctions and infarct size. Superoxide dismutase types 1 and 2 (SOD1 and SOD2), glutathione peroxidase types 1 and 3 (GPX 1 and GPX3) and catalase mRNA levels were assessed by quantitative RT-PCR to investigate the potential role of antioxidant enzymes.

RESULTS

Thyrotoxicosis elicited cardiac hypertrophy and increased baseline mechanical performance, including increased left ventricle (LV) systolic pressure, LV developed pressure and derivatives of pressure (dP/dt), whereas in hypothyroid hearts exhibited decreased dP/dt. Post-ischemic recovery of LV end-diastolic pressure (LVEDP), LVDP and dP/dt was impaired in thyrotoxic rat hearts, whereas hypothyroid hearts exhibited improved LVEDP and decreased infarct size. Catalase expression was decreased by thyrotoxicosis.

CONCLUSION

Thyrotoxicosis was correlated, at least in part, to cardiac remodeling and increased susceptibility to IR injury possibly due to down-regulation of antioxidant enzymes, whereas hypothyroid hearts were less vulnerable to IR injury.

The Relationship between Subclinical Thyroid Disease and Cardiovascular Disease Risk Score in Koreans

Subclinical hyperthyroidism and subclinical hypothyroidism are characterized by abnormal thyroid stimulating hormone (TSH) with normal free thyroxine. Subclinical thyroid diseases, to date, have received less attention compared with other thyroid diseases since they are asymptomatic. This study aimed to verify the association between subclinical thyroid diseases and cardiovascular diseases (CVDs) risk score in the Korean population. This was a population-based cohort study using data collected from 3,722 subjects (aged ≥ 30 years) during the 6th Korea National Health and Nutrition Examination Survey (KNHANES VI; 2013-2015). Gender-specific Framingham risk scores were calculated to identify the association between subclinical thyroid diseases and 10-year CVD risk score. Complex survey, with consideration of sampling weight, was analyzed using generalized linear models after stratification by gender. The TSH reference range was between 0.61 and 6.91 mIU/L in this study. TSH showed a positive association with the 10-year CVD risk score only in the female population (P = 0.001). There were significant differences in the least squares means of 10-year CVD risk score by the effect of subclinical hypothyroidism compared with euthyroidism (normal group) in females, after adjusting for body mass index, white blood cell, and urine iodine (P = 0.006 and Bonferroni corrected P = 0.012). In conclusion, subclinical hypothyroidism is associated with increased 10-year CVD risk score in the female Korean population aged 30 years or more. Therefore, we recommend to clinically checkup major CVD risk factors in female patients with subclinical hypothyroidism aged 30 years or more.

Metabolic reprogramming via PPARα signaling in cardiac hypertrophy and failure: From metabolomics to epigenetics

Studies using omics-based approaches have advanced our knowledge of metabolic remodeling in cardiac hypertrophy and failure. Metabolomic analysis of the failing heart has revealed global changes in mitochondrial substrate metabolism. Peroxisome proliferator-activated receptor-α (PPARα) plays a critical role in synergistic regulation of cardiac metabolism through transcriptional control. Metabolic reprogramming via PPARα signaling in heart failure ultimately propagates into myocardial energetics. However, emerging evidence suggests that the expression level of PPARα per se does not always explain the energetic state in the heart. The transcriptional activities of PPARα are dynamic, yet highly coordinated. An additional level of complexity in the PPARα regulatory mechanism arises from its ability to interact with various partners, which ultimately determines the metabolic phenotype of the diseased heart. This review summarizes our current knowledge of the PPARα regulatory mechanisms in cardiac metabolism and the possible role of PPARα in epigenetic modifications in the diseased heart. In addition, we discuss how metabolomics can contribute to a better understanding of the role of PPARα in the progression of cardiac hypertrophy and failure.