Free thyroxine within the normal reference range predicts risk of atrial fibrillation

Thyroid-related Hormones and Hypertension Incidence in Middle-Aged and Older Hispanic/Latino Adults: The HCHS/SOL Study

Background

Thyroid-related hormones act to regulate metabolic pathways and blood pressure (BP). However, the relationship of TSH and peripheral thyroid hormones and the role of the hypothalamic-pituitary-thyroid axis on hypertension development is not fully understood. We assessed sex-specific associations of thyroid-related hormones with BP and hypertension in Hispanic/Latino adults followed for 6 years.

Methods

We studied 1789 adults, ages 45 to 74, free of diabetes at baseline from a subcohort of the Hispanic Community Health Study/Study of Latinos. We assessed TSH, free T4 (FT4), T3, and various indicators of thyroid axis. Using multivariable linear and Poisson regression adjusted for survey design and confounding variables, we estimated a priori sex-specific associations of thyroid-related hormones with changes in BP and hypertension development.

Results

In men and women, TSH and TSH/FT4 ratios were associated with changes in diastolic BP and T3 with changes in pulse pressure and the development of hypertension from prehypertension. In men, a 1-SD increase in TSH [incident rate ratio (IRR) = 1.42; 95% confidence interval (CI): 1.15, 1.75] and TSH/FT4 ratio (IRR = 1.20; 95% CI: 1.07, 1.35) were positively associated with the development of hypertension from prehypertension while the TSH/FT4 ratio (IRR = 0.85; 95% CI: .72, 1.00) was protective in women. We observed sex-specific differences in associations of the T3/FT4 ratio and indices of pituitary sensitivity to thyroid hormones with changes in pulse pressure and hypertension development.

Conclusion

Thyroid-related hormones are associated with sex-specific changes in BP and hypertension among Hispanic/Latino adults consistent with selected studies conducted in other populations. Mechanisms underlying associations of pituitary sensitivity to thyroid hormones with BP and hypertension development warrant further study.

Prognostic implications of thyroid disease in patients with atrial fibrillation

Atrial fibrillation (AF) is often accompanied by thyroid disease (THD). This study aimed to explore the relationship between THD and the occurrence of significant clinical outcomes in patients with AF. This post hoc analysis utilized data from the MISOAC-AF trial (NCT02941978), which enrolled hospitalized patients with AF. Patients were categorized based on their THD history into hyperthyroidism, hypothyroidism, or euthyroidism. Cox regression models were employed to calculate unadjusted and adjusted hazard ratios (aHRs). The primary outcomes of interest included all-cause mortality, cardiovascular death, and hospitalizations during the follow-up period. The study included 496 AF patients (mean age 73.09 ± 11.10 years) with available THD data, who were followed-up for a median duration of 31 months. Among them, 16 patients (3.2%) had hyperthyroidism, 141 (28.4%) had hypothyroidism, and 339 (68.4%) had no thyroid disease. Patients with hypothyroidism exhibited higher rates of hospitalization during follow-up (aHR: 1.57, 95% CI 1.12 to 2.20, p = 0.025) compared to the euthyroid group. Elevated levels of thyroid-stimulating hormone (TSH) were correlated with an increased risk of cardiovascular mortality (aHR: 1.03, 95% CI 1.01 to 1.05, p = 0.007) and hospitalizations (aHR: 1.06, 95% CI 1.01 to 1.12, p = 0.03). Conversely, lower levels of triiodothyronine (T3) were associated with higher risks of all-cause mortality (aHR: 0.51, 95% CI 0.31 to 0.82, p = 0.006) and cardiovascular mortality (aHR: 0.42, 95% CI 0.23 to 0.77, p = 0.005). Among patients with AF, hypothyroidism was associated with increased hospitalizations. Furthermore, elevated TSH levels and decreased T3 levels were linked to higher cardiovascular and all-cause mortality risks, respectively.

Effects of Triiodothyronine Treatment in an Animal Model of Heart Failure with Preserved Ejection Fraction

Background: Low levels of triiodothyronine (T3) are common in patients with heart failure (HF). Our aim was to evaluate the effects of supplementation with low and replacement doses of T3 in an animal model of HF with preserved ejection fraction (HFpEF). Methods: We evaluated four groups: ZSF1 Lean (n = 8, Lean-Ctrl), ZSF1 Obese (rat model of metabolic-induced HFpEF, n = 13, HFpEF), ZSF1 Obese treated with a replacement dose of T3 (n = 8, HFpEF-T3high), and ZSF1 Obese treated with a low-dose of T3 (n = 8, HFpEF-T3low). T3 was administered in drinking water from weeks 13 to 24. The animals underwent anthropometric and metabolic assessments, echocardiography, and peak effort testing with maximum O2 consumption (VO2max) determination at 22 weeks, and a terminal hemodynamic evaluation at 24 weeks. Afterwhile myocardial samples were collected for single cardiomyocyte evaluation and molecular studies. Results: HFpEF animals showed lower serum and myocardial thyroid hormone levels than Lean-Ctrl. Treatment with T3 did not normalize serum T3 levels, but increased myocardial T3 levels to normal levels in the HFpEF-T3high group. Body weight was significantly decreased in both the T3-treated groups, comparing with HFpEF. An improvement in glucose metabolism was observed only in HFpEF-T3high. Both the treated groups had improved diastolic and systolic function in vivo, as well as improved Ca2+ transients and sarcomere shortening and relaxation in vitro. Comparing with HFpEF animals, HFpEF-T3high had increased heart rate and a higher rate of premature ventricular contractions. Animals treated with T3 had higher myocardial expression of calcium transporter ryanodine receptor 2 (RYR2) and α-myosin heavy chain (MHC), with a lower expression of β-MHC. VO2max was not influenced by treatment with T3. Myocardial fibrosis was reduced in both the treated groups. Three animals died in the HFpEF-T3high group. Conclusions: Treatment with T3 was shown to improve metabolic profile, myocardial calcium handling, and cardiac function. While the low dose was well-tolerated and safe, the replacement dose was associated with increased heart rate, and increased risk of arrhythmias and sudden death. Modulation of thyroid hormones may be a potential therapeutic target in HFpEF; however, it is important to take into account the narrow therapeutic window of T3 in this condition.

An elevated parametric thyroid feedback quantile-based index is associated with atrial fibrillation

INTRODUCTION

Atrial fibrillation is associated with hyperthyroidism. Within the euthyroid range, it is also associated with high thyroxine (fT4), but not with thyrotropin (TSH). We aim to describe differences in thyroid regulation, measured by the Parametric Thyroid Feedback Quantile-Based Index (PTFQI), between patients with atrial fibrillation and the general population.

MATERIALS AND METHODS

Thyroid parameters (PTFQI, TSH, and fT4) of a sample of 84 euthyroid subjects with atrial fibrillation (cases) were compared to a reference sample of euthyroid healthcare patients (controls). We calculated age and sex adjusted ORs for atrial fibrillation across tertiles of these parameters. Also, within cases, we studied thyroid parameters association with clinical characteristics of the atrial fibrillation.

RESULTS

After adjusting for age and sex, fT4 and PTFQI were higher in subjects with atrial fibrillation when compared to the general sample (p<0.01 and p=0.01, respectively). Atrial fibrillation ORs of the third versus the first PTFQI tertile was 1.88(95%CI 1.07,3.42), and there was a gradient across tertiles (p trend=0.02). Among atrial fibrillation patients, we observed that higher PTFQI was associated with sleep apnea/hypopnea syndrome (OSAS) (p=0.03), higher fT4 was associated with the presence of an arrhythmogenic trigger (p=0.02) and with heart failure (p<0.01), and higher TSH was also associated with OSAS (p<0.01).

CONCLUSIONS

Euthyroid subjects with atrial fibrillation have an elevation of the pituitary TSH-inhibition threshold, measured by PTFQI, with respect to the general population. Within atrial fibrillation patients, high PTFQI was associated with OSAS, and high fT4 with heart failure. These results hint of the existence of a relationship between thyroid regulation and atrial fibrillation.

Mechanisms and Management of Thyroid Disease and Atrial Fibrillation: Impact of Atrial Electrical Remodeling and Cardiac Fibrosis

Atrial fibrillation (AF) is the most common cardiac arrhythmia associated with increased cardiovascular morbidity and mortality. The pathophysiology of AF is characterized by electrical and structural remodeling occurring in the atrial myocardium. As a source of production of various hormones such as angiotensin-2, calcitonin, and atrial natriuretic peptide, the atria are a target for endocrine regulation. Studies have shown that disorders associated with endocrine dysregulation are potential underlying causes of AF. The thyroid gland is an endocrine organ that secretes three hormones: triiodothyronine (T3), thyroxine (T4) and calcitonin. Thyroid dysregulation affects the cardiovascular system. Although there is a well-established relationship between thyroid disease (especially hyperthyroidism) and AF, the underlying biochemical mechanisms leading to atrial fibrosis and atrial arrhythmias are poorly understood in thyrotoxicosis. Various animal models and cellular studies demonstrated that thyroid hormones are involved in promoting AF substrate. This review explores the recent clinical and experimental evidence of the association between thyroid disease and AF. We highlight the current knowledge on the potential mechanisms underlying the pathophysiological impact of thyroid hormones T3 and T4 dysregulation, in the development of the atrial arrhythmogenic substrate. Finally, we review the available therapeutic strategies to treat AF in the context of thyroid disease.

The bidirectional relationship of thyroid disease and atrial fibrillation: Established knowledge and future considerations

Atrial fibrillation (AF) tends to occur frequently in patients with thyroid disease, primarily hyperthyroidism. In hyperthyroidism, increased levels of thyroid hormones, via intra- and extranuclear mechanisms, have profound effects on cardiac electrophysiology. Hypothyroidism carries a lower risk for AF and is mainly associated with the overtreatment of hypothyroid patients. New-onset AF is frequently the only manifestation of thyroid disease, which renders screening for thyroid dysfunction in that scenario clinically useful. Managing thyroid disease and comorbid AF is essential. This includes thyroid hormones control along with conventional AF therapy. However, there are several open issues with this comorbid duo. The optimal management of thyroid disease and its impact on AF burden remains obscure. There is scanty information on clear-cut benefits for therapy of subclinical thyroid disease and screening of asymptomatic patients. Furthermore, the immunogenetic overlap between the autoantibodies in Graves' disease and AF genesis may lead to novel therapeutic implications. The objective of this review is to summarize the up-to-date epidemiology, pathogenesis, pathophysiology and management of interacting thyroid disease and AF.

Effects of thyroid dysfunction and thyroid stimulating hormone levels on the Atrial fibrillation risks: a systematic review and dose-response meta-analysis from cohort studies

OBJECTIVE

To explore the relationship between thyroid dysfunction, thyroid stimulating hormone (TSH) levels and risks of atrial fibrillation (AF) in studies as well as to conduct a dose-response meta-analysis on the correlation between TSH levels and AF risks.

METHODS

13 studies from five databases with 649,293 subjects (mean age 65.1 years) were included. The dose-response meta-analysis was conducted by comparing the Risk Ratios (RRs) and 95% Confidence Intervals (CI) for incident AF associated with different levels of TSH (vs TSH=0 mU/L) across studies. Data were collected until Oct 25, 2021.

RESULTS

Subclinical hyperthyroidism, subclinical hypothyroidism, clinical hyperthyroidism were associated with the increased risk of AF respectively (RR=1.70, 95% CI: 1.11-2.62; RR=1.23, 95% CI:1.05-1.44; RR=2.35, 95% CI:1.07-5.16), while clinical hypothyroidism was not found associated with the significantly increased risk of AF (RR=1.20, 95% CI: 0.72-1.99). A non-linear relationship was observed in two models (crude model: P_nonlinear<0.001; adjusted model: P_nonlinear =0.0391) between the TSH concentrations and the risks of AF.

CONCLUSIONS

Our study indicated that subclinical hyperthyroidism, subclinical hypothyroidism, clinical hyperthyroidism were associated with the risk of AF, and the results for TSH levels and AF risk were mixed which showed a U-shaped relationship.

Association of thyroid function, within the euthyroid range, with cardiovascular risk: The EPIPorto study

BACKGROUND

Thyroid hormones are important modulators of cardiovascular function. Both hypothyroidism and hyperthyroidism are known to contribute to an increased cardiovascular risk. It remains uncertain whether thyroid hormones level within the euthyroid range are associated with cardiometabolic risk. We aimed to evaluate the association between thyroid function levels within the euthyroid range and cardiovascular risk in a population-based cohort.

METHODS

Eight hundred thirty-five subjects aged ≥45 years from the EPIPorto population-based cohort were included. We excluded participants with TSH, free T4 (FT4), or free T3 (FT3) outside of the reference range, or with previous cardiovascular or thyroid disease. The associations between thyroid function, cardiovascular risk factors and the 10-year estimated risk of cardiovascular events (using SCORE2 and SCORE2-OP) were evaluated in linear and logistic regression models, crudely and adjusting for age, sex, BMI, diabetes, and smoking.

RESULTS

The mean age of the participants was 61.5 (SD 10.5) years and 38.9% were men. Eleven percent of the participants had diabetes, 47.8% had dyslipidemia, and 54.8% had hypertension. The mean body mass index (BMI) was 27.4 (SD 4.6) kg/m², and the median (percentile25-75) 10-year risk of cardiovascular events was 5.46% (2.92, 10.11). Participants with higher BMI, larger waist circumference and higher hs-CRP had higher levels of FT3 and FT3/FT4 ratio. Lower FT3/FT4 ratio and higher FT4 levels were associated with higher prevalence of diabetes and more adverse lipid profile. Higher TSH, lower FT3 and lower FT3/FT4 ratio were associated with lower eGFR. Lower FT3, lower FT3/FT4 ratio and higher FT4 were associated with an increased 10-year risk of cardiovascular events.

CONCLUSIONS

In a population-based study, variations of thyroid function within the euthyroid range were associated with cardiovascular risk factors. On one hand, individuals with higher BMI, larger waist circumference and higher hs-CRP had higher levels of FT3 and FT3/FT4 ratio. On the other hand, a decreased conversion of T4 to T3 (lower FT3, lower FT3/FT4 ratio and/or higher FT4) was associated with a higher prevalence of diabetes, a more adverse lipid profile, a lower eGFR and an increased 10-year risk of cardiovascular events.

Impact of thyroid disease in patients with atrial fibrillation: Analysis from the JoFib registry

Background

Thyroid disease is a well-established risk factor for atrial fibrillation (AF). However, only a handful of studies examined its impact on treatment. This study aims to report the prevalence rate of thyroid disease in patients with AF and to demonstrate the effect of thyroid disease on AF treatment.

Materials and methods

We retrospectively analyzed the Jordanian Atrial Fibrillation Study (JoFib). Among Jordan and Palestine, patients with AF were evaluated for their sociodemographic, clinical, and pharmacological characteristics.

Results

A total of 2000 patients with AF (53.3% males, mean age 67.6 ± 13.1 years) were enrolled in the JoFib registry from May 2019 to November 2020. Thyroid disease was present in 210 (10.5%) patients. Hypertension, diabetes mellitus, and dyslipidemia were the most common comorbidities among patients with thyroid history (75.2%, 51.0%, and 45.7%, respectively). Diabetes mellitus (p = .04), pulmonary hypertension (p = .01), and chronic kidney disease (p = .01) were significantly higher in this particular subgroup. Patients with thyroid disease demonstrated significantly higher usage of anticoagulants (p = .02).

Conclusion

Despite having similar stroke and bleeding risks, patients with thyroid disease demonstrated meaningful differences in their baseline characteristics. Prospective studies are required to assess the influence of thyroid hormone fluctuations on the progression of AF.

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Thyroid disease doesn't appear to impact bleeding risk in atrial fibrillation.

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Patients with thyroid disease are more likely to consume more anticoagulants.

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Thyroid disease in atrial fibrillation maybe linked with pulmonary hypertension.

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Assessment tools of stork or bleeding may be underestimated in Arab Jordanians.

Higher FT4 level within the normal range predicts the outcome of cryoballoon ablation in paroxysmal atrial fibrillation patients without structural heart disease

Background

Accumulated evidence has indicated that a high‐normal FT4 level is an independent risk factor for the clinical progression of AF. However, the association between elevated FT4 concentration within the normal range and AF recurrence after cryoballoon ablation in China is unknown.

Methods

This retrospective and observational study included 453 AF patients who underwent cryoballoon ablation from January 2016 to August 2018. Patients were classified into quartiles based on preprocedural serum FT4 concentration. The clinical characteristics of the patients and the long‐term rate of AF recurrence after ablation were assessed.

Results

After a mean follow‐up period of 17.4 ± 9.0 months, 91 (20.1%) patients suffered from AF recurrence. The AF recurrence rate by FT4 quartile was 17.7%, 19.0%, 21.4%, and 22.3% for participants with FT4 in quartile 1, 2, 3, and 4, respectively (p < .001). On multivariate Cox regression, FT4 concentration (HR: 1.187, 95% CI: 1.093–1.290, p < .001) and left atrial diameter (HR: 1.052, 95% CI: 1.014–1.092, p = .007) were significant predictors of AF recurrence. When stratifying for AF type, the rate of postoperative recurrence was independently increased as FT4 concentration increased in paroxysmal AF, but not in persistent AF (p < .001 in paroxysmal AF and p = .977 in persistent AF).

Conclusion

Higher FT4 level within the normal range predicted the outcome of cryoballoon ablation in Chinese paroxysmal AF patients without structural heart disease.

High-Normal Thyroid Function and Recurrence of Atrial Fibrillation after Catheter Ablation: A Prospective Observational Study

BACKGROUND

Thyroid function is increasingly recognized as an important modifiable factor for atrial fibrillation (AF); however, it is unclear if the changes in thyroid hormones, even within the normal range, are associated with AF recurrence after catheter ablation.

METHODS

Consecutive paroxysmal AF patients who underwent catheter ablation were enrolled. Patients with abnormal thyroid hormones or previous thyroid illnesses were excluded. Patients were followed for 12 months or until they presented with the first episode of atrial tachyarrhythmia after a blanking period.

RESULTS

The study included 448 patients with a mean age of 61 (14) years, and 46% were women. After a 1-year follow-up, 104 (23.2%) patients experienced atrial tachyarrhythmia recurrences after an ablation procedure. Recurrence was significantly different among quartile groups of thyroid function, with highest FT4 and FT3 levels associated with the greatest risk of recurrence (p < 0.001 and p = 0.024, respectively). FT4 and FT3 levels were independent predictors of atrial tachyarrhythmia recurrence (hazard ratio 1.07 per 1 pmol/L increase in FT4, 95% confidence interval [CI] 1.01-1.15, p = 0.036 and 1.31 per 1 pmol/L increase in FT3, 95% CI 1.01-1.71, p = 0.032).

CONCLUSIONS

High-normal FT3 and FT4 levels are associated with AF recurrence after catheter ablation in this Chinese population. Attention to thyroid hormones could be valuable to assist in the management of AF.

Genetic Thyrotropin Regulation of Atrial Fibrillation Risk Is Mediated Through an Effect on Height

CONTEXT

A genetic predisposition to lower thyrotropin (TSH) levels is associated with increased atrial fibrillation (AF) risk through undefined mechanisms.

OBJECTIVE

Defining the genetic mediating mechanisms could lead to improved targeted therapies to mitigate AF risk.

METHODS

We used 2-sample mendelian randomization (MR) to test associations between TSH-associated single-nucleotide variations and 16 candidate mediators. We then performed multivariable mendelian randomization (MVMR) to test for a significant attenuation of the genetic association between TSH and AF, after adjusting for each mediator significantly associated with TSH.

RESULTS

Four candidate mediators (free thyroxine, systolic blood pressure, heart rate, and height) were significantly inversely associated with genetically predicted TSH after adjusting for multiple testing. In MVMR analyses, adjusting for height significantly decreased the magnitude of the association between TSH and AF from -0.12 (SE 0.02) occurrences of AF per SD change in height to -0.06 (0.02) (P = .005). Adjusting for the other candidate mediators did not significantly attenuate the association.

CONCLUSION

The genetic association between TSH and increased AF risk is mediated, in part, by taller stature. Thus, some genetic mechanisms underlying TSH variability may contribute to AF risk through mechanisms determining height occurring early in life that differ from those driven by thyroid hormone-level elevations in later life.

Liothyronine and Desiccated Thyroid Extract in the Treatment of Hypothyroidism

Background: The basis for the treatment of hypothyroidism with levothyroxine (LT4) is that humans activate T4 to triiodothyronine (T3). Thus, while normalizing serum thyrotropin (TSH), LT4 doses should also restore the body's reservoir of T3. However, there is evidence that T3 is not fully restored in LT4-treated patients. Summary: For patients who remain symptomatic on LT4 therapy, clinical guidelines recommend, on a trial basis, therapy with LT4+LT3. Reducing the LT4 dose by 25 mcg/day and adding 2.5-7.5 mcg liothyronine (LT3) once or twice a day is an appropriate starting point. Transient episodes of hypertriiodothyroninemia with these doses of LT4 and LT3 are unlikely to go above the reference range and have not been associated with adverse drug reactions. Trials following almost a 1000 patients for almost 1 year indicate that similar to LT4, therapy with LT4+LT3 can restore euthyroidism while maintaining a normal serum TSH. An observational study of 400 patients with a mean follow-up of ∼9 years did not indicate increased mortality or morbidity risk due to cardiovascular disease, atrial fibrillation, or fractures after adjusting for age when compared with patients taking only LT4. Desiccated thyroid extract (DTE) is a form of combination therapy in which the LT4/LT3 ratio is ∼4:1; the mean daily dose of DTE needed to normalize serum TSH contains ∼11 mcg T3, but some patients may require higher doses. The DTE remains outside formal FDA oversight, and consistency of T4 and T3 contents is monitored by the manufacturers only. Conclusions: Newly diagnosed hypothyroid patients should be treated with LT4. A trial of combination therapy with LT4+LT3 can be considered for those patients who have unambiguously not benefited from LT4.