Subclinical hyperthyroidism and atrial fibrillation

Effect of Hyperthyroidism Treatments on Heart Rate Variability: A Systematic Review and Meta-Analysis

The reversibility of HRV abnormalities in hyperthyroidism remains contradictory. The design of this study involves conducting a systematic review and meta-analysis on the effect of antithyroid treatments on HRV in hyperthyroidism. PubMed, Cochrane, Embase, and Google Scholar were searched until 4 April 2022. Multiple reviewers selected articles reporting HRV parameters in treated and untreated hyperthyroidism. Independent data extraction by multiple observers was stratified by degree of hyperthyroidism for each HRV parameter: RR intervals, SDNN (standard deviation of RR intervals), RMSSD (square root of the mean difference of successive RR intervals), pNN50 (percentage of RR intervals with >50 ms of variation), total power (TP), LFnu (low-frequency normalized unit) and HFnu (high-frequency), VLF (very low-frequency), and LF/HF ratio. We included 11 studies for a total of 471 treated hyperthyroid patients, 495 untreated hyperthyroid patients, and 781 healthy controls. After treatment, there was an increase in RR, SDNN, RMSSD, pNN50, TP, HFnu, and VLF and a decrease in LFnu and LF/HF ratio (p < 0.01). Overt hyperthyroidism showed similar results, in contrast to subclinical hyperthyroidism. Compared with controls, some HRV parameter abnormalities persist in treated hyperthyroid patients (p < 0.05) with lower SDNN, LFnu, and higher HFnu, without significant difference in other parameters. We showed a partial reversibility of HRV abnormalities following treatment of overt hyperthyroidism. The improvement in HRV may translate the clinical cardiovascular benefits of treatments in hyperthyroidism and may help to follow the evolution of the cardiovascular morbidity.

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.

Estimated change in prevalence of abnormal thyroid-stimulating hormone levels in China according to the application of the kit-recommended or NACB standard reference interval

BACKGROUND

Both the kit-recommended and United States National Academy of Clinical Biochemistry (NACB) standard thyroid-stimulating hormone (TSH) reference intervals (RIs) are used to determine thyroid dysfunction in clinical practice and epidemiological surveys in China. However, a number of kit-recommended RIs were derived from the European or United States reference population.

METHODS

A nationally representative cross-sectional study with 78,470 enrolled participants aged 18 years or older from China was performed. Serum concentrations of thyroid hormones, TSH, thyroid antibodies (by Roche Diagnostics), and urine iodine concentration (UIC) were measured.

FINDINGS

The abnormal TSH weighted prevalence was 15.33% (95% CI, 14.24% to 16.49%) according to the kit-recommended RI and 6.89% (6.46% to 7.34%) according to the NACB standard RI. The NACB standard prevalence of abnormal TSH was associated with an absolute change in abnormal TSH prevalence of -11.20% (-12.23% to -10.18%) among women. When estimating the proportion of supranormal TSH levels according to background characteristics, the NACB standard definition decreased the prevalence by more than 10% in some categories, with the highest absolute difference of -13.92% (-15.52% to -12.33%) observed among the elderly, -12.85% (-13.68% to -12.02%) among those with UIC ≥300 μg/L, and -12.15% (-13.02% to -11.28%) among non-smokers. For subnormal TSH, with the highest absolute difference of 3.17% (2.74% to 3.61%) observed among regular smokers, 3.11% (2.49% to 3.74%) among the elderly, and 2.53% (2.29% to 2.77%) among those with BMI <25.

INTERPRETATION

For adults in China, the NACB standard RI of TSH reveals a lower estimated prevalence of supranormal TSH levels than the kit-recommended RI. Because of the public health significance of overt and subclinical hypothyroidism and the very large population base in China, the TSH RI should be further assessed.

FUNDING

National Health Commission of the People's Republic of China and National Natural Science Foundation of China.

Myocardial disease and ventricular arrhythmia in Marfan syndrome: a prospective study

Background

Aortic root dilatation and—dissection and mitral valve prolapse are established cardiovascular manifestations in Marfan syndrome (MFS). Heart failure and arrhythmic sudden cardiac death have emerged as additional causes of morbidity and mortality.

Methods

To characterize myocardial dysfunction and arrhythmia in MFS we conducted a prospective longitudinal case–control study including 86 patients with MFS (55.8% women, mean age 36.3 yr—range 13–70 yr–) and 40 age—and sex-matched healthy controls. Cardiac ultrasound, resting and ambulatory ECG (AECG) and NT-proBNP measurements were performed in all subjects at baseline. Additionally, patients with MFS underwent 2 extra evaluations during 30 ± 7 months follow-up. To study primary versus secondary myocardial involvement, patients with MFS were divided in 2 groups: without previous surgery and normal/mild valvular function (MFS-1; N = 55) and with previous surgery or valvular dysfunction (MFS-2; N = 31).

Results

Compared to controls, patients in MFS-1 showed mild myocardial disease reflected in a larger left ventricular end-diastolic diameter (LVEDD), lower TAPSE and higher amount of (supra) ventricular extrasystoles [(S)VES]. Patients in MFS-2 were more severely affected. Seven patients (five in MFS-2) presented decreased LV ejection fraction. Twenty patients (twelve in MFS-2) had non-sustained ventricular tachycardia (NSVT) in at least one AECG. Larger LVEDD and higher amount of VES were independently associated with NSVT.

Conclusion

Our study shows mild but significant myocardial involvement in patients with MFS. Patients with previous surgery or valvular dysfunction are more severely affected. Evaluation of myocardial function with echocardiography and AECG should be considered in all patients with MFS, especially in those with valvular disease and a history of cardiac surgery.

Cancer Survivorship in Primary Care

With the early detection of cancer and improvement in cancer therapy, the number of cancer survivors is rapidly increasing. This number is expected to reach 2 million by the end of 2019. Cancer survivors struggle with not only cancer-related health problems but also diverse acute and chronic diseases. These health issues make cancer survivorship more complex, and proper care coordination is necessary. This study aimed to summarize the definition of cancer experience and management of cancer survivors, specifically focused on gastric, colorectal, lung, breast, thyroid, prostate, and cervical cancers. Furthermore, it aimed to discuss the role of primary care in cancer survivorship and survivorship care models and the National Policy for Cancer Survivors and Future Challenges.

Relationship between heart rate variability and subclinical thyroid disorders of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

The association between subclinical thyroid dysfunctions and autonomic modulation changes has been described by many studies with conflicting results. We aimed to analyze the association between subclinical hyperthyroidism (SCHyper), subclinical hypothyroidism (SCHypo), and heart rate variability (HRV) using the baseline from ELSA-Brasil. SCHyper and SCHypo were classified by use of medication to treat thyroid disorders, thyrotropin levels respectively above and under the reference range, and normal free thyroxine levels. For HRV, the participants underwent 10 min in supine position and the R-R intervals of the final 5 min were selected for analysis. We first used linear regression models to report crude data and then, multivariate adjustment for sociodemographic (age, sex, and race) and cardiovascular risk factors (hypertension, dyslipidemia, diabetes, smoking, body mass index, use of alcohol, and leisure physical activity) using the euthyroid group as reference. From 9270 subjects (median age, 50; interquartile range: 44–56), 8623 (93.0%) were classified as euthyroid, 136 (1.5%) as SCHyper, and 511 (5.5%) as SCHypo. Compared to euthyroid subjects, SCHyper participants presented significantly higher heart rate (68.8 vs 66.5 for euthyroidism, P=0.007) and shorter R-R intervals (871.4 vs 901.6, P=0.007). Although SCHyper was associated with lower standard deviation of NN interval (SDNN) (β: –0.070; 95% confidence interval (95%CI): –0.014 to –0.009) and low-frequency (LF) (β: –0.242, 95%CI: –0.426 to –0.058) compared to the euthyroid group, these differences lost significance after multivariate adjustment for confounders. No significant differences were found for HRV in SCHypo. No association was found between HRV and SCHyper or SCHypo compared to euthyroid subjects in this sample of apparently healthy subjects.

Is heart disease a risk factor for low dementia test battery scores in older persons with Down syndrome? Exploratory, pilot study, and commentary

OBJECTIVES

Certain heart conditions and diseases are common in Down syndrome (DS; trisomy 21), but their role in early onset dementia that is prevalent in older adults with DS has not been evaluated. To address this knowledge gap, we conducted a study of risk factors for low neurocognitive/behavioral scores obtained with a published dementia test battery (DTB). Participants were adults with DS living in New York (N = 29; average age 46 years). We asked three questions. 1. Does having any type of heart disease affect the association between DTB scores and chronological age? 2. Does thyroid status affect the association between heart disease and DTB scores? 3. Are the E4 or E2 alleles of apolipoprotein E (APOE) associated with DTB scores or with heart disease?

METHOD

The study was retrospective, pilot, and exploratory. It involved analysis of information in a database previously established for the study of aging in DS. Participants had moderate intellectual disability on average. Information for each person included: gender, age, a single DTB score obtained by combining results from individual subscales of the DTB, the presence or absence of heart disease, thyroid status (treated hypothyroidism or normal), and APOE genotype. Trends were visualized by inspection of graphs and contingency tables. Statistical methods used to evaluate associations included Pearson correlation analysis, Fisher's exact tests (2-tailed), and odds ratio analysis. P values were interpreted at the 95% confidence level without Bonferroni correction. P values >.05<.1 were considered trends.

RESULTS

The negative correlation between DTB scores and age was significant in those with heart disease but not in those without. Heart disease was significantly associated with DTB scores >1 SD below the sample mean; there was a strong association between heart disease and low DTB scores in those with treated hypothyroidism but not in those with normal thyroid status. The APOE genotype was weakly associated with heart disease (E4, predisposing; E2, protective) in males.

CONCLUSIONS

On the basis of the potentially important findings from the present study, large prospective studies are warranted to confirm and extend the observations. In these, particular heart conditions or diseases and other medical comorbidities in individuals should be documented.

Thyroid hormones and cardiovascular disease

Myocardial and vascular endothelial tissues have receptors for thyroid hormones and are sensitive to changes in the concentrations of circulating thyroid hormones. The importance of thyroid hormones in maintaining cardiovascular homeostasis can be deduced from clinical and experimental data showing that even subtle changes in thyroid hormone concentrations - such as those observed in subclinical hypothyroidism or hyperthyroidism, and low triiodothyronine syndrome - adversely influence the cardiovascular system. Some potential mechanisms linking the two conditions are dyslipidaemia, endothelial dysfunction, blood pressure changes, and direct effects of thyroid hormones on the myocardium. Several interventional trials showed that treatment of subclinical thyroid diseases improves cardiovascular risk factors, which implies potential benefits for reducing cardiovascular events. Over the past 2 decades, accumulating evidence supports the association between abnormal thyroid function at the time of an acute myocardial infarction (MI) and subsequent adverse cardiovascular outcomes. Furthermore, experimental studies showed that thyroid hormones can have an important therapeutic role in reducing infarct size and improving myocardial function after acute MI. In this Review, we summarize the literature on thyroid function in cardiovascular diseases, both as a risk factor as well as in the setting of cardiovascular diseases such as heart failure or acute MI, and outline the effect of thyroid hormone replacement therapy for reducing the risk of cardiovascular disease.

Subclinical Thyroid Dysfunction and Frailty Among Older Men

CONTEXT

Both subclinical thyroid dysfunction and frailty are common among older individuals, but data on the relationship between these 2 conditions are conflicting.

OBJECTIVE

The purpose of this study was to assess the cross-sectional and prospective associations between subclinical thyroid dysfunction and frailty and the 5 frailty subdomains (sarcopenia, weakness, slowness, exhaustion, and low activity).

SETTING AND DESIGN

The Osteoporotic Fractures in Men Study is a prospective cohort study.

PARTICIPANTS

Men older than 65 years (n = 1455) were classified into 3 groups of thyroid status: subclinical hyperthyroidism (n = 26, 1.8%), subclinical hypothyroidism (n = 102, 7.0%), and euthyroidism (n = 1327, 91.2%).

MAIN OUTCOME MEASURES

Frailty was defined using a slightly modified Cardiovascular Health Study Index: men with 3 or more criteria were considered frail, men with 1 to 2 criteria were considered intermediately frail, and men with no criteria were considered robust. We assessed the cross-sectional relationship between baseline thyroid function and the 3 categories of frailty status (robust/intermediate/frail) as well as the prospective association between baseline thyroid function and subsequent frailty status and mortality after a 5-year follow-up.

RESULTS

At baseline, compared with euthyroid participants, men with subclinical hyperthyroidism had an increased likelihood of greater frailty status (adjusted odds ratio, 2.48; 95% confidence interval, 1.15-5.34), particularly among men aged <74 years at baseline (odds ratio for frailty, 3.63; 95% confidence interval, 1.21-10.88). After 5 years of follow-up, baseline subclinical hypothyroidism and hyperthyroidism were not consistently associated with overall frailty status or frailty components.

CONCLUSION

Among community-dwelling older men, subclinical hyperthyroidism, but not subclinical hypothyroidism, is associated with increased odds of prevalent but not incident frailty.

Safety Profile and Effects of Pulsed Methylprednisolone on Vital Signs in Thyroid Eye Disease

Objective. To analyze changes in vital signs (heart rate (HR), systolic (SBP), and diastolic blood pressure (DBP)) during and after intravenous methylprednisolone (IVMP) and any other adverse effects. Methods. Retrospective review of charts of patients who received IVMP as treatment regime for thyroid eye disease. All subjects had vital signs charted during and after infusions. Results. This study included 38 subjects and a total of 242 infusions administered. IVMP resulted in a small but significant percentage drop in mean SBP at 30 min (p < 0.001) and 60 min (p = 0.03) but no difference at 90 min. There was also small but significant percentage drop in mean DBP and HR (DBP: p < 0.001 for 30 min, p = 0.001 for 60 min, and p = 0.02 for 90 min and HR: p < 0.001 for 30 min, 60 min, and 90 min). There were no cumulative effects on change of blood pressure or HR. There were 6 episodes of bradycardia (2.5%) and 12 episodes of moderate to severe hypertension (5%). No significant cardiovascular or hepatic toxicity was found. Conclusion. IVMP is relatively safe and efficacious. IVMP demonstrated mild and noncumulative effects on vital signs. Severe hypertension may occur in susceptible individuals such as those with underlying hypertension and uncontrolled thyroid dysfunction, whereas bradycardia may be more likely in those on beta-blockers.

Subclinical thyroid dysfunction and functional capacity among elderly

BACKGROUND

Subclinical thyroid dysfunction is common among older people and has been associated with decreased functional capacity but with conflicting data. The aim of this study was to assess the association between subclinical thyroid dysfunction and functional capacity in an elderly population.

METHODS

We included 5182 participants with a mean age of 75.2 years from the Prospective Study of Pravastatin in the Elderly at Risk (PROSPER). Self-reported functional capacity was assessed using the Barthel Index (BI) and the Instrumental Activities of Daily Living (IADL) scores at baseline and during follow-up. Participants with subclinical hyperthyroidism (n=65) and subclinical hypothyroidism (n=173) were compared to euthyroid participants (n=4944). The association between persistent subclinical thyroid dysfunction and functional capacity and decline was also investigated.

RESULTS

At baseline, compared to euthyroid participants (BI 19.73±SE 0.06; IADL 13.52±0.02), there was no difference in functional capacity for participants with subclinical hyperthyroidism (BI 19.60±0.09; IADL 13.51±0.12, p>0.05) or subclinical hypothyroidism (BI 19.82±0.06; IADL 13.55±0.08, p>0.05). Over a mean 3.2-year follow-up period, there was no association between thyroid function and annual decline of either BI or IADL (p>0.05). No association was found between persistent subclinical thyroid dysfunction and functional capacity at baseline or during follow-up (p>0.05). Results were similar after excluding participants with a maximum BI and/or IADL score at baseline.

CONCLUSION

Among well-functioning community-dwelling elderly, we found no evidence that subclinical thyroid dysfunction contributes to decreased functional capacity.

Thyroid hormones and electrocardiographic parameters: findings from the third national health and nutrition examination survey

Introduction

Altered thyroid status exerts a major effect on the heart. Individuals with hypo- or hyperthyroidism showed various changes in electrocardiograms. However, little is known about how variations in thyroid hormone levels within the normal range affect electrical activities of the heart in the general population.

Methods and Results

We conducted a cross-sectional analysis of 5,990 men and women from the Third National Health and Nutrition Examination Survey. Serum total T4 was measured by immunoassay and TSH was measured by chemiluminescent assay. We categorized T4 and TSH into 7 groups with cut-offs at the 5^th, 20^th, 40^th, 60^th, 80^th, and 95^th percentiles of the weighted population distribution. Electrocardiographic parameters were measured from the standard 12-lead electrocardiogram. We found a positive linear association between serum total T4 level and heart rate in men, and a U-shape association between T4 and PR interval in men and women. TSH level was positively associated with QRS interval in men, while a U-shape association between TSH and QRS was observed in women. No clear graded association between thyroid hormones and corrected QT or JT was found, except that men in the highest category of T4 levels appeared to have longer corrected QT and JT, and men in the lowest category of T4 appeared to have shorter corrected QT and JT.

Conclusions

Variation in thyroid hormone levels in the general population, even within the normal range, was associated with various ECG changes.

Previously unknown thyroid dysfunction in patients with acute ischemic stroke

OBJECTIVES

Opinions differ regarding the clinical significance of subclinical thyroid disorders. The aim of the present study was to evaluate the prevalence and influence of previously unknown overt or subclinical thyroid dysfunction in patients with acute ischemic stroke and to look for differences between cardio-embolic and non-embolic ischemic stroke.

MATERIAL AND METHODS

A total of 153 Swedish patients diagnosed with first-time acute ischemic stroke were included in the study and categorized for suspected cardio-embolic (n = 30) or non-embolic (n = 123) ischemic stroke depending on the presence of atrial fibrillation (AF). Blood samples were taken 48 h or earlier after onset of stroke symptoms.

RESULTS

Previously, unknown overt or subclinical thyroid dysfunction was found in 12%. Previously, unknown overt or subclinical hyperthyroidism was more common in the AF group (13%) compared to the non-AF group (3%), P = 0.048. Patients with AF had slightly higher concentrations of free T4 (15 vs 14 pm; P < 0.001), but there was no significant difference in concentrations of S-TSH or prevalence of thyroperoxidase (TPO) antibodies between the groups.

CONCLUSIONS

In patients with first-time acute ischemic stroke, unknown thyroid dysfunction is common, and unknown overt or subclinical hyperthyroidism is associated with cardio-embolic stroke.

Thyrotoxicosis

Hyperthyroidism describes the sustained increase in thyroid hormone biosynthesis and secretion by a thyroid gland with increased metabolism. Although the use of radioiodine scanning serves as a useful surrogate that may help characterize the cause of thyrotoxicosis, it only indirectly addresses the underlying physiologic mechanism driving the increase in serum thyroid hormones. In this article, thyrotoxic states are divided into increased or decreased thyroid metabolic function. In addition to the diagnosis, clinical presentation, and treatment of the various causes of hyperthyroidism, a section on functional imaging and appropriate laboratory testing is included.

A review on cardiovascular diseases originated from subclinical hypothyroidism

Thyroid hormones play an important role on the cardiovascular systems and thyroid disorder ultimately have a profound adverse effects on myocardium and vascular functions. There are extensive reports on the role of overt thyroid dysfunction which adversely can modify the cardiovascular metabolism but even at the present of some controversial reports, the subclinical thyroid disorders are able also to manipulate cardiovascular system to some extent. The aim of this study is to review the cardiovascular disorders accompanied with subclinical hypothyroidism. It is concluded that adverse effect of thyroid malfunction on myocardium and vascular organs are through the direct role of thyroid hormone and dyslipidemia on heart muscle cells at nuclear level and vascular system, respectively. It seems many cardiovascular disorders initially would not have been occurred in the first place if the thyroid of affected person had functioned properly, therefore thyroid function tests should be one of a prior laboratory examinations in cardiovascular disorders.

Prognosis of thyroid function after hemithyroidectomy

Identify criteria and create a risk scoring system to predict hypothyroidism after hemithyroidectomy. We have retrospectively studied 216 cases of patients with goiter who had undergone hemithyroidectomy from January 2002 to December 2007 at Vilnius University Hospital Santariškių Klinikos. Patients were divided into two groups according to their thyroid function after hemithyroidectomy: 168 (77.8%) patients’ thyroid function was normal (group A), 48 (22.2%) patients had symptoms of hypothyroidism (group B). The relationship between groups and parameters such as patients’ sex, age, patient’s weight, preoperative serum thyroid-stimulating hormone (TSH) level, weight of the remnant gland, ratio of the remaining thyroid gland weight to patient’s weight was statistically analysed. The patients’ mean age was 41.6 ± 14.1 years in group A and 52.9 ± 13.9 years in group B (p=0.0002). The mean preoperative TSH level was 0.79 ± 0.5 mU/L in group A, compared with 1.42 ± 1.00 mU/L in group B (p= 0.005). The mean ratio of the remaining thyroid gland weight to patient’s weight was 0.102 ± 0.053 g/kg in group A and 0.063 ± 0.027 g/kg in group B (p=0.04). The groups did not establish a significant difference between patients’ sex, patient’s weight or weight of the remaining gland. Patient’s age, preoperative serum TSH level, ratio of the remaining thyroid gland weight to patient’s weight is the main factors of hypothyroidism after hemithyroidectomy. A risk scoring system was created to predict hypothyroidism after hemithyroidectomy before the operation.

Subclinical hypothyroidism and subclinical hyperthyroidism

Subclinical thyroid dysfunction occurs when peripheral thyroid hormone levels are within the normal laboratory reference range and the serum thyroid-stimulating hormone (TSH or thyrotropin) level is greater than normal (subclinical hypothyroidism) or less than normal (subclinical hyperthyroidism; TSH normal laboratory reference range: 0.3-5.0 mIU/l). For patients with subclinical hypothyroidism (serum TSH levels >10 mIU/l), thyroxine therapy is prescribed if other causes of TSH elevation and transient conditions have been excluded. For serum TSH levels between 5.0 and 10.0 mIU/l, selective therapy should be considered. For patients with sustained subclinical hyperthyroidism (serum TSH levels <0.1 mIU/l), therapy is recommended, especially in older patients. Observation or selective therapy should be considered for patients with serum TSH levels between 0.1 and 0.3 mIU/l.

Thyroid hormones and cardiac arrhythmias

Thyroid hormone plays an important role in cardiac electrophysiology and Ca2+ handling through both genomic and nongenomic mechanisms of action, while both actions can interfere. Chronic changes in the amount of circulating thyroid hormone due to thyroid dysfunction or systemic disease result in structural, electrophysiological and Ca2+ handling remodeling, while acute changes may affect basal activity of cardiac cells membrane systems. Consequently, long-term or rapid modulation of sarcolemmal ion channels, Ca2+ cycling proteins and intercellular communicating channels by thyroid hormone may affect heart function as well as susceptibility of the heart to arrhythmias. This aspect including pro- and anti-arrhythmic potential of thyroid hormone is highlighted in this review.

Cardiac hypertrophy and thyroid hormone signaling

Thyroid hormone exerts a large number of influences on the cardiovascular system. Increased thyroid hormone action increases the force and speed of systolic contraction and the speed of diastolic relaxation and these are largely beneficial effects. Furthermore, thyroid hormone has marked electrophysiological effects increasing heart rate and the propensity for atrial fibrillation and these effects are largely mal-adaptive. In addition, thyroid hormone markedly increases cardiac angiogenesis and decreases vascular tone. These multiple thyroid hormone effects are largely mediated by the action of nuclear based thyroid hormone receptors (TR) the thyroid hormone receptor alpha and beta. TRα is the predominant isoform in the heart. Rapid nongenomic thyroid hormone effects also occur, which can be clearly demonstrated in ex-vivo experiments. Some of the most marked thyroid hormone effects in cardiac myocytes involve influences on calcium flux, with thyroid hormone promoting expression of the gene encoding the calcium pump of the sarcoplasmic reticulum (SERCa2). In contrast, in hypothyroid animals phospholamban levels, which inhibit the SERCa2 pump, are increased. In addition, marked effects are exerted on the calcium channel of the sarcoplasmic reticulum the ryanodine channel. Related to myofibrillar proteins, myosin heavy chain alpha is increased by T3 and MHC beta is decreased. Complex and interesting interactions occur between cardiac hypertrophy induced by excess thyroid hormone action and cardiac hypertrophy occurring with heart failure. The thyroid hormone mediated cardiac hypertrophy in its initial phases presents a physiological hypertrophy with increases in SERCa2 levels and decreased expression of MHC beta. In contrast, pressure overload induced heart failure leads to a “pathological” cardiac hypertrophy which is largely mediated by activation of the calcineurin system and the MAPkinases signaling system. Recent evidence indicates that heart failure can lead to a downregulation of the thyroid hormone signaling system in the heart. In the failing heart, decreases of thyroid hormone receptor levels occur. In addition, serum levels of T4 and T3 are decreased with heart failure in the frame of the non-thyroidal illness syndrome. The decrease in T3 serves as an indicator for a bad prognosis in the heart failure patient being linked to increased mortality. In animal models, it can be shown that in pressure overload-induced cardiac hypertrophy a decrease of thyroid hormone receptor levels occurs. Cardiac function can be improved by increasing expression of thyroid hormone receptors mediated by adeno-associated virus based gene transfer. The failing heart may develop a “hypothyroid” status contributing to diminished cardiac contractile function.

Thyroid hormone and myocardial ischaemia

Thyroid hormone has various effects on the cardiovascular system and its effects on cardiac contractility, heart rhythm and vascular function has long been recognized. However, new evidence is emerged on the importance of thyroid hormone in the response of the myocardium to ischaemic stress and cardiac remodelling following myocardial infarction. Based on this new information, this review highlights the role of thyroid hormone in myocardial ischaemia and cardiac remodelling, the possible underlying mechanisms and the potential therapeutic implications. Thyroid hormone or analogs may prove new therapeutic agents for treating ischaemic heart disease.

Review: The association of thyroid dysfunction with all-cause and circulatory mortality: is there a causal relationship?

CONTEXT

Currently there is ongoing debate on whether subclinical and overt thyroid dysfunction may exert deleterious effects on the cardiovascular system with the consequence of increased mortality in affected individuals. We systematically review studies on the relation of thyroid dysfunction with all-cause and circulatory mortality questioning whether thyroid dysfunction is a causal factor for mortality.

METHODS

Two investigators independently searched the MEDLINE database. All case-control and cohort studies published in peer-reviewed journals were selected. Studies on nonthyroidal illness or low-T3 syndrome and reports from highly selected populations were not considered. Risk estimates from studies with appropriate adjustment for confounders were metaanalyzed.

RESULTS

Four among eight studies performed to investigate the association between hyperthyroidism and mortality revealed an increased risk of either all-cause or circulatory mortality. Only the minority of studies, however, adjusted analyses for relevant confounders besides age, sex, and race. Studies after radioiodine therapy were generally biased by indication. Findings from 11 studies that investigated the relation between hypothyroidism and mortality were highly discrepant and partly even mutually exclusive. Some of these discrepancies are explained by confounding and selection.

CONCLUSIONS

The currently available evidence for a causal relation of both hyperthyroidism and hypothyroidism with mortality is weak and should particularly not be used to decide whether patients with subclinical thyroid conditions should be treated. Very old individuals might represent an exception from this rule and may benefit from mildly reduced thyroid function, but this has to be substantiated by further research.

Hypothyroidism following Hemithyroidectomy for Benign Nontoxic Thyroid Disease

Hypothyroidism following hemithyroidectomy for benign nontoxic thyroid disease is an underappreciated phenomenon. Up until recently, it was common practice for physicians to place post-hemithyroidectomy patients on thyroid suppression therapy during the immediate postoperative period. That practice began to fall out of favor as a result of two developments: (1) the publication of data that put into question the efficacy of levothyroxine therapy for preventing recurrent disease or thyroid growth and (2) a heightened awareness of the morbidity associated with levothyroxine. We conducted a retrospective chart-review study of 58 patients with benign nontoxic thyroid disease who had undergone hemithyroidectomy from 1994 through 2003 at one institution. Of these 58 patients, 14 (24.1%) had become hypothyroid after surgery, including 7 who had been so diagnosed 1 month postoperatively and 6 at 2 months. The remaining 44 patients were euthyroid. The mean preoperative serum thyroid-stimulating hormone (TSH) levels in the hypothyroid and the euthyroid groups were 2.39 and 1.07 μIU/ml, respectively—a statistically significant difference (p < 0.0001). A tissue diagnosis consistent with chronic inflammation (lymphocytic thyroiditis or Hashimoto's thyroiditis) was found in 50.0% of the hypothyroid patients, compared with only 6.8% of the euthyroid patients—again, a significant difference (p < 0.001). No significant difference was seen between the two groups with respect to age, sex, or the weight of the resected gland. We conclude that hypothyroidism after hemithyroidectomy is not an uncommon occurrence. Apparent risk factors include a high mean preoperative serum TSH level and tissue pathology consistent with chronic inflammation. It may be wise to follow patients with these identifiable risk factors more closely during the postoperative period; monitoring should include scheduled serial serum TSH draws.

Thyroid hormone use, hyperthyroidism and mortality in older women

PURPOSE

Thyroid dysfunction is common, particularly among older women. The safety of thyroid hormone use and long-term prognosis of hyperthyroidism remain controversial. We performed a prospective cohort study to examine the relationship among thyroid hormone use, previous hyperthyroidism, abnormal thyroid function, and mortality.

METHODS

We studied 9449 community-dwelling white women aged > or =65 years followed for 12 years. For analyses of thyroid function, we performed a nested case-cohort in 487 women using a third-generation thyroid-stimulating hormone assay. Causes of death were adjudicated based on death certificates and hospital records.

RESULTS

Twelve percent of the 9449 women took thyroid hormone at baseline, and the mean duration of thyroid hormone use was 15.8 years; 9.4% of participants reported a history of hyperthyroidism. During 12 years of follow-up, 3159 women died (33%). In multivariate analysis, mortality among users of thyroid hormone was similar to that observed for nonusers (relative hazard [RH] 1.11, 95% confidence interval [CI], 0.98-1.24, P=.09). Previous hyperthyroidism was associated with a higher risk of all-cause mortality (RH 1.20, 95% CI, 1.06-1.36), particularly cardiovascular mortality (RH 1.46, 95% CI, 1.20-1.77). Low (< or /=0.5 mU/L) or high (>5 mU/L) thyroid-stimulating hormone levels were not associated with excess total or cause-specific mortality, but the power to detect these relationships was limited.

CONCLUSIONS

Among older women, thyroid hormone use is not associated significantly with excess mortality, but previous hyperthyroidism may be associated with a small increase in all-cause and cardiovascular mortality. Additional long-term studies of hyperthyroidism and its treatment should further explore these findings.

Blood coagulation, fibrinolytic activity and lipid profile in subclinical thyroid disease: subclinical hyperthyroidism increases plasma factor X activity

BACKGROUND AND OBJECTIVES

Various abnormalities of coagulation and fibrinolysis occur in patients with thyroid diseases, and may range from subclinical laboratory abnormalities to clinically significant disorders of coagulation and, rarely, major haemorrhage or thromboembolism. The influence of subclinical hypothyroidism (SHypo) on haemostasis is controversial, both hypercoagulable and hypocoagulable states have been reported. A hypercoagulable state might be a risk factor for thromboembolic disease in SHypo. On the other hand, subclinical hyperthyroidism (SCHyper) is associated with enhanced cardiovascular risk. In the English literature, there are no studies on changes in coagulation and fibriolytic status in subjects with SCHyper. Therefore, the aim of the present study was to investigate the markers of endogenous coagulation and fibrinolysis, and to evaluate the relationships between serum lipid profile and thyroid hormones and these haemostatic parameters in subclinical thyroid patients.

DESIGN AND METHODS

Various haemostatic parameters were investigated in 30 patients with SHypo and 20 patients with SCHyper and compared to 20 euthyroid controls. Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, factors V, VII, VIII, IX and X activities, vWF, antithrombin III (AT III), protein C, protein S, tissue plasminogen activator (t-PA) and tissue plasminogen activator inhibitor-1 (PAI-1), as well as common lipid variables, were measured. The relationships between serum thyroid hormones and these haemostatic parameters were examined.

RESULTS

Compared with the control subjects, only FX activity was significantly increased in patients with SCHyper (P < 0.01). Total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels were significantly higher in patients with SHypo compared with the control group (P < 0.001 and P < 0.01, respectively). TC levels were significantly higher in patients with SCHyper than in controls (P < 0.05). No differences could be found in coagulation/fibrinolysis parameters between subclinical hypothyroid patients and control subjects. In patients with SCHyper, serum TSH level was positively correlated with FX activity (r: 0.58, P < 0.01) and inversely correlated with PAI-1 (r: -0.55. P < 0.05). Serum TG levels were inversely correlated with plasma activities of factors V, VII, VIII, IX, X and vWF (r: -0.83, P < 0.001; r: -0.68, P < 0.05; r: -0.61, P < 0.05; r: -0.77, P < 0.01; r: -0.63, P < 0.05; r: -0.60, P < 0.05, respectively). Serum TC levels were positively correlated with plasma fibrinogen levels (r: 0.72, P < 0.05). Serum HDL-C levels were positively correlated with protein S activity (r: 0.68, P < 0.05) and negatively correlated with F VII activity (r: -0.69, P < 0.05). Also, in patients with SHypo, serum TG levels were positively correlated with serum TSH levels (r: 0.42, P < 0.05), plasma activities of factors V, VII and X (r: 0.42, P < 0.05; r: 0.54, P < 0.01; r: 0.57, P < 0.01, respectively) and negatively correlated with plasma fibrinogen levels (r: -0.41, P < 0.05). Serum TC levels were positively correlated with factors V and X (r: 0.42, P < 0.05; r: 0.58, P < 0.01, respectively) and negatively correlated with t-PA Ag levels (r: -0.44, P < 0.05). Serum HDL-C levels were inversely correlated with F VII activity (r: -0.48, P < 0.05).

INTERPRETATION AND CONCLUSIONS

Some differences were found in the haemostatic parameters and lipid profile between the subclinical thyroid patients and healthy controls. Increased factor X activity in patients with subclinical hyperthyroidism represent a potential hypercoagulable state, which might augment the already existing risk for atheroscleroic complications. Also, subclinical hypothyroid patients exhibit a more atherogenic lipid profile compared with healthy individuals. Therefore, subclinical hypothyroidism is also associated with an increased risk of cardiovascular disease. However, thyroid hormones may play a role at different levels of the complex haemostatic system in subclinical thyroid disease.

Sympatho-vagal control of heart rate variability in patients treated with suppressive doses of L-thyroxine for thyroid cancer

OBJECTIVE

This study aimed to analyze the autonomic control of heart rate variability (HRV) in subjects receiving chronic l-thyroxine (l-T4) treatment after total thyroidectomy and (131)I therapy for differentiated thyroid carcinoma.

METHODS

Blood pressure (BP) and sympatho-vagal activity (evaluated by power spectral analysis (PSA) of time-domain parameters of HRV) were studied in clinostatism and after orthostatism in 24 healthy controls, and in 12 patients taking l-T4 (125-200 mug/day) to maintain serum TSH levels at <0.01 muIU/ml. The study of HRV by PSA is a non-invasive method of analyzing sympatho-vagal control of HRV by quantifying high-frequency (HF) (0.15-0.4 Hz) and low-frequency (LF) (0.04-0.15 Hz) powers.

RESULTS

Patients on L-T4 treatment had undetectable TSH levels, serum free T4 (fT4) above the normal range or at the upper limit in one case, and normal free tri-iodothyronine (fT3) levels. Heart rate and R-R intervals were not different in the two groups, both in clinostatism and in ortostatism. Systolic and mean BP were higher in patients than in controls and were inversely correlated with actual serum fT4 levels. During clinostatism, thyroid patients showed significantly lower LF power (P = 0.035), LF/(LF + HF) (P = 0.008) and LF/HF (P = 0.01) than controls. When patients moved from lying to standing, there was a significantly different decrease in orthostatic LF power (P = 0.001), LF/(LF + HF) (P = 0.044) and LF/HF (P = 0.047) versus controls.

CONCLUSIONS

Changes in autonomic control of HRV, characterized by decreased sympathetic activity and impaired sympatho-vagal balance with preserved vagal tone, are detectable in patients with hyperthyroxinemia due to suppressive l-T4 therapy and increased systolic and mean, but not diastolic, BP.

Simple electrocardiographic markers for the prediction of paroxysmal atrial fibrillation in hyperthyroidism

BACKGROUND

Hyperthyroidism is a major cause of paroxysmal atrial fibrillation (AF). The purpose of this study was to evaluate the predictors of AF in the patients with clinical and subclinical hyperthyroidism.

METHODS AND RESULTS

The study population consisted of four groups: group I (57 euthyroid healthy persons), group II (33 patients with subclinical hyperthyroidism), group III (69 patients with overt hyperthyroidism) and group IV (31 patients with overt hyperthyroidism and documented paroxysmal AF). The maximum P wave duration (P maximum) in group IV (114 +/- 8 ms) was significantly higher than group I (102 +/- 7 ms, p < 0.001), group II (106 +/- 7 ms, p < 0.001) and group III (108 +/- 9 ms, p0.005). The P wave dispersion (PWD) was measured as 46 +/- 9 ms in group IV and this was significantly higher than group I (29 +/- 8 ms, p < 0.001), group II (36 +/- 9 ms, p < 0.001) and grup III (38 +/- 8 ms, p = 0.001). The P maximum and PWD were higher in the patients with subclinical hyperthyroidism compared to healthy individuals. Univariate regression analysis revealed that age, P maximum and PWD, multivariate analysis showed that P maximum and PWD were significant predictors of paroxysmal AF. A PWD value of 37.5 ms separated group IV from others with a sensitivity of 90%, specificity of 85%, and positive predictive accuracy of 77%.

CONCLUSION

Simply measuring P maximum and PWD values, we could identify the patients with high risk for the development of AF and these simple ECG parameters may help in clinical judgement to determine the requirement for treatment in the patients with subclinical hyperthyroidism.

Subclinical hyperthyroidism: clinical features and treatment options

Subclinical hyperthyroidism appears to be a common disorder. It may be caused by exogenous or endogenous factors: excessive TSH suppressive therapy with L-thyroxine (L-T4) for benign thyroid nodular disease, differentiated thyroid cancer, or hormone over-replacement in patients with hypothyroidism are the most frequent causes. Consistent evidence indicates that 'subclinical' hyperthyroidism reduces the quality of life, affecting both the psycho and somatic components of well-being, and produces relevant signs and symptoms of excessive thyroid hormone action, often mimicking adrenergic overactivity. Subclinical hyperthyroidism exerts many significant effects on the cardiovascular system; it is usually associated with a higher heart rate and a higher risk of supraventricular arrhythmias, and with an increased left ventricular mass, often accompanied by an impaired diastolic function and sometimes by a reduced systolic performance on effort and decreased exercise tolerance. It is well known that these abnormalities usually precede the onset of a more severe cardiovascular disease, thus potentially contributing to the increased cardiovascular morbidity and mortality observed in these patients. In addition, it is becoming increasingly apparent that subclinical hyperthyroidism may accelerate the development of osteoporosis and hence increased bone vulnerability to trauma, particularly in postmenopausal women with a pre-existing predisposition. Subclinical hyperthyroidism and its related clinical manifestations are reversible and may be prevented by timely treatment.

Thyroid, hemostasis and thrombosis

The aim of this paper is to briefly review some practical aspects of the relationship between thyroid function and several disorders of the hemostatic system in terms of bleeding and thrombosis. Thrombocytopenia, acquired hemophilia, hypercoagulability, cardioembolism and other biochemical coagulative and fibrinolytic abnormalities have been described in the past years both in hyper- and hypothyroidism. Since most of hyper- and hypothyroid conditions are the consequence of autoimmune thyroid disease (1), either deranged immune function, altered circulating thyroid hormone concentration, or both may concur in the pathogenesis of hemostatic disorders of potential crucial clinical impact. These aspects will be outlined and discussed in an attempt to give answers to some questions, often arising in the clinical approach.

Disfunções mínimas da tiróide: hipotiroidismo subclínico e hipertiroidismo subclínico

Hipotiroidismo subclínico (SHT) e hipertiroidismo subclínico (SCH) são definidos pelas concentrações normais de T4 e T3 livres séricos associadas com valores de TSH elevado (SHT) ou suprimido (SCH). As prevalências são baixas e sintomas e sinais de disfunção tiroideana escassos. No SHT, colesterol total e LDL-C estão ligeiramente elevados, e tratamento com levotiroxina pode influir nos valores dos lipídeos. Ocorre diminuição da contratilidade do miocárdio e aumento da resistência vascular periférica, que melhoram com o tratamento. Fibrilação atrial é mais freqüente no SCH, e há aumento do índice de massa do ventrículo esquerdo, da contratilidade cardíaca, disfunção diastólica e indução de batimentos atriais ectópicos que regridem com uso de beta-bloqueadores. No SCH, ocorre diminuição da densidade óssea. Depressão, doença do pânico e alterações de testes cognitivos são freqüentes no SHT. O tratamento do SHT é indicado com TSH sérico maior do que 8mU/L e presença de anticorpos antitiroideanos, e do SCH endógeno, quando existem sintomas, em idosos ou concentração de TSH menor do que 0,1mU/L.

Mortality rate of chronically ill geriatric patients with subnormal serum thyrotropin concentration: a 2-yr follow-up study

We investigated the natural course of subclinical thyroid dysfunctions in geriatric patients, especially regarding their association with mortality rate. Ninety-three randomly selected chronically ill geriatric patients 64- 87 (median: 77) yr of age participated in the screening study with a 2-yr follow-up. Serum thyrotropin (thyroid- stimulating hormone [TSH]), free thyroxine, triiodothyronine, and antibodies against thyroid peroxidase were measured. During the follow-up, patients with suppressed TSH levels who were otherwise euthyroid (untreated) had a higher mortality rate than patients with normal TSH (5/8 vs 18/64; p < 0.05). The initial clinical state of these two subgroups did not differ significantly. Two-thirds of patients with treated hyperthyroidism died. The mortality rate of patients with initially subnormal but not suppressed TSH level was average and did not differ statistically from either the euthyroid or the hyperthyroid groups. Only 1 of 13 euthyroid patients with positive thyroid antibody titers developed a subsequent subclinical hypothyroidism. Subclinical hyperthyroidism was found to be associated with a higher mortality rate in chronically ill geriatric patients, which justifies screening for thyroid dysfunction and treatment of subclinical hyperthyroidism. In addition, a subnormal but measurable TSH was not indicative regarding the future development of hyperthyroidism. Finally, during the 2-yr follow-up, antibody positivity in the euthyroid cases did not prove to be predictive for the subsequent development of hypothyroidism.

Subclinical thyroid disorders: the menace of the Trojan horse

This review aims at summarizing some new data regarding the so-called subclinical thyroid disease and incorporate the knowledge in order to provide a basis for a more careful approach to these morbidities. SHyper represents a considerable risk factor for atrial fibrillation in the elderly and also for osteoporosis, which is a major cause of morbidity in postmenopausal women. SHypo is not an innocuous condition. It progresses to thyroid failure in patients with positive thyroid antibodies, it affects neurobehavior, it may influence cardiac contractility at exercise and it is associated with an impaired lipid profile that may provoke atherosclerosis. Therefore, both conditions should be screened more carefully in the community and treatment should be more often considered.