Myocardial mechanics in hyperthyroidism: importance of left ventricular loading conditions, heart rate and contractile state

The genetic association between hyperthyroidism and heart failure: a Mendelian randomization study

Background and aims

Hyperthyroidism is an endocrine disease with multiple etiologies and manifestations. Heart failure (HF) is a common, costly, and deadly medical condition in clinical practice. Numerous studies have suggested that abnormal thyroid function can induce or aggravate the development of heart disease. However, no study has demonstrated a causal relationship between hyperthyroidism and heart failure. Therefore, the purpose of this study was to explore the causal link between hyperthyroidism and HF.

Methods

Summary data for genetically predicted hyperthyroidism were obtained from a genetic association study. The data examined for genetically determined all-cause heart failure came from 218,208 individuals from the FinnGen Consortium. Two-sample Mendelian randomization (MR) analysis was used to estimate the causal link between hyperthyroidism and heart failure. Statistical analyses were conducted using the inverse variance-weighted, weighted median, simple median, weighted mode, MR-PRESSO (number of distribution = 5000), MR-Egger, and leave-one-out.

Results

The results of the inverse-variance weighted analysis indicated a causal association between hyperthyroidism and an increased risk of all-cause heart failure (IVW: β=0.048, OR=1.049, 95%CI: [1.013 to 1.087], P=0.007). Similarly, the weighted median approach demonstrated a positive correlation between hyperthyroidism and all-cause heart failure (OR=1.049, [95% CI, 1.001-1.100]; P=0.044). Additionally, no horizontal pleiotropy or heterogeneity was observed. The leave-one-out analysis revealed that the majority of the SNP-driven associations were not influenced by a single genetic marker.

Conclusion

Our study observed a causal relationship between hyperthyroidism and all-cause heart failure. Hyperthyroidism may associate with heart failure genetically.

Thyrotoxicosis-Induced Cardiomyopathy With Systolic Dysfunction

Thyrotoxicosis-induced dilated cardiomyopathy is a rare but potentially life-threatening complication of thyrotoxicosis, with an incidence of <1%. This condition is characterized by a dilatation of the ventricular chamber and a decrease in cardiac contractility. Untreated, it can lead to irreversible changes in cardiac structure and function, including dilated ventricular chamber, a decrease in ejection fraction (EF), and an increased risk of atrial fibrillation. We present a case of a 39-year-old patient with a diagnosis of thyrotoxicosis-induced acute heart failure. A two-dimensional (2D) echocardiogram disclosed an ejection fraction of 36%, with diffuse mild dilation of the atria and ventricles with trace mitral and tricuspid regurgitation. The anti-thyroid-stimulating hormone (TSH) receptor was positive, and Grave's disease was diagnosed. The patient eventually returned to baseline functional status and could return to basic activities of daily living without limitations. The patient was encouraged to follow up with outpatient cardiology. Early diagnosis of cardiac involvement in patients with thyrotoxicosis is critical. Promptly delivered intensive treatment with the rapid achievement of euthyroid state can potentially reverse cardiac dysfunction and improve patient outcomes.

Role of thyroid hormones-induced oxidative stress on cardiovascular physiology

Thyroid hormones (THs) play an essential role in the maintenance of cardiovascular homeostasis and are involved in the modulation of cardiac contractility, heart rate, diastolic function, systemic vascular resistance, and vasodilation. THs have actions on cardiovascular physiology through the activation or repression of target genes or the activation of intracellular signals through non-genomic mechanisms. Hyperthyroidism alters certain intracellular pathways involved in the preservation of the structure and functionality of the heart, causing relevant cardiovascular disorders. Reactive oxygen species (ROS) play an important role in the cardiovascular system, but the exacerbated increase in ROS caused by chronic hyperthyroidism together with regulation on the antioxidant system have been associated with the development of cardiovascular dysfunction. In this review, we analyze the role of THs-induced oxidative stress in the cellular and molecular changes that lead to cardiac dysfunction, as well as the effectiveness of antioxidant treatments in attenuating cardiac abnormalities developed during hyperthyroidism.

Neutrophil-to-lymphocyte Ratio is Associated with LV Diastolic Dysfunction in the Overt Hyperthyroid Patients

BACKGROUND

Recent studies have shown that the neutrophil-to-lymphocyte ratio (NLR) has gradually been identified as a more reliable marker of inflammation, with predictive value for the development of many diseases. However, its association with left ventricular (LV) diastolic dysfunction in overt hyperthyroid patients is unclear. Here, we aimed to explore the relationship between NLR and LV diastolic dysfunction in overt hyperthyroid patients.

METHODS

For this study, we retrospected the consecutive medical files of 350 overt hyperthyroid patients. Their medical data and laboratory findings were recorded. According to the presence or absence of LV diastolic dysfunction, the patients with overt hyperthyroidism were divided into two groups. One group with LV diastolic dysfunction included 104 patients and another group with non-LV diastolic dysfunction included 246 patients. The NLR values between the two groups were compared, and the relationship between NLR levels and the prevalence of LV diastolic dysfunction was also explored.

RESULTS

The NLR value in LV diastolic dysfunction group in the overt hyperthyroid subjects was significantly higher than that in non-LV diastolic dysfunction group [1.100 (0.907-1.580) vs 1.000 (0.761-1.405), P=0.016]. The prevalence of LV diastolic dysfunction in Low- (NLR<0.879), Medium- (0.879< NLR<1.287), and High- (NLR >1.287) NLR level groups were 20.9%, 32.5% and 35.7% respectively. Moreover, increased NLR is associated with increased prevalence of LV diastolic dysfunction, and after adjustment for potential associated factors, NLR remained significantly associated with LV diastolic dysfunction. (OR = 11.753, 95%CI = 1.938-71.267, P = 0.007).

CONCLUSIONS

Our findings demonstrated that the NLR was associated with LV diastolic dysfunction in the overt hyperthyroid patients, and the prevalence of LV diastolic dysfunction may be positively correlated with NLR levels.

Arterial Stiffness and Blood Pressure in Patients Newly Diagnosed with Graves' Disease Compared with Euthyroid Controls

INTRODUCTION AND OBJECTIVE

The excess cardiovascular morbidity and mortality in hyperthyroidism and Graves' disease (GD) is inadequately understood. We aimed to elucidate whether well-established cardiovascular risk factors such as arterial stiffness in terms of pulse wave velocity (PWV) and blood pressure differ in GD and controls.

METHODS

This was a cross-sectional study comparing 55 hyperthyroid patients with newly diagnosed GD and 55 euthyroid, population-based controls matched for age, sex and menopausal status. PWV and blood pressure were measured in office (SphygmoCor Xcel) and 24-h ambulatory settings (Arteriograph). Differences between groups were assessed using adjusted linear regression analysis.

RESULTS

Compared to controls, GD patients showed higher PWV in the 24-h but not in the office setting with an adjusted 24-h PWV difference of 1.0 (95% CI: 0.6-1.5) m/s. PWV was higher in GD at both day and night, and nightly PWV dipping was lower (-5.5, 95% CI: -10.4 to -0.6%). Furthermore, central and brachial pulse pressure was significantly higher in both the office and 24-h setting, whereas nightly central pulse pressure dipping was significantly lower in GD (-5.4, 95% CI: -10.5 to -0.2%). Mean arterial pressure did not differ between the groups.

CONCLUSIONS

Despite comparable blood pressure, GD is associated with a higher 24-h PWV that was not detected in the office setting. Pulse pressure was higher in GD, whereas mean arterial pressure did not differ between the groups. Longitudinal studies should pursue whether higher PWV might be a piece to the puzzle of understanding the increased risk of cardiovascular disease in hyperthyroidism and GD.

Thyroid and Cardiovascular Disease: Research Agenda for Enhancing Knowledge, Prevention, and Treatment

Thyroid hormones have long been known to have a range of effects on the cardiovascular system. However, significant knowledge gaps exist concerning the precise molecular and biochemical mechanisms governing these effects and the optimal strategies for management of abnormalities in thyroid function in patients with and without preexisting cardiovascular disease. In September 2017, the National Heart, Lung, and Blood Institute convened a Working Group with the goal of developing priorities for future scientific research relating thyroid dysfunction to the progression of cardiovascular disease. The Working Group reviewed and discussed the roles of normal thyroid physiology, the consequences of thyroid dysfunction, and the effects of therapy in 3 cardiovascular areas: cardiac electrophysiology and arrhythmias, the vasculature and atherosclerosis, and the myocardium and heart failure. This report describes the current state of the field, outlines barriers and challenges to progress, and proposes research opportunities to advance the field, including strategies for leveraging novel approaches using omics and big data. The Working Group recommended research in 3 broad areas: (1) investigation into the fundamental biology relating thyroid dysfunction to the development of cardiovascular disease and into the identification of novel biomarkers of thyroid hormone action in cardiovascular tissues; (2) studies that define subgroups of patients with thyroid dysfunction amenable to specific preventive strategies and interventional therapies related to cardiovascular disease; and (3) clinical trials focused on improvement in cardiovascular performance and cardiovascular outcomes through treatment with thyroid hormone or thyromimetic drugs.

Thyroid and Cardiovascular Disease: Research Agenda for Enhancing Knowledge, Prevention, and Treatment

Thyroid hormones have long been known to have a range of effects on the cardiovascular system. However, significant knowledge gaps exist concerning the precise molecular and biochemical mechanisms governing these effects and the optimal strategies for management of abnormalities in thyroid function in patients with and without preexisting cardiovascular disease. In September 2017, The National Heart, Lung, and Blood Institute convened a Working Group with the goal of developing priorities for future scientific research relating thyroid dysfunction to the progression of cardiovascular disease. The Working Group reviewed and discussed the roles of normal thyroid physiology, the consequences of thyroid dysfunction, and the effects of therapy in three cardiovascular areas: cardiac electrophysiology and arrhythmias, the vasculature and atherosclerosis, and the myocardium and heart failure. This report describes the current state of the field, outlines barriers and challenges to progress, and proposes research opportunities to advance the field, including strategies for leveraging novel approaches using omics and big data. The Working Group recommended research in three broad areas: 1) investigation into the fundamental biology relating thyroid dysfunction to the development of cardiovascular disease and into the identification of novel biomarkers of thyroid hormone action in cardiovascular tissues; 2) studies that define subgroups of patients with thyroid dysfunction amenable to specific preventive strategies and interventional therapies related to cardiovascular disease; and 3) clinical trials focused on improvement in cardiovascular performance and cardiovascular outcomes through treatment with thyroid hormone or thyromimetic drugs.

G protein-coupled estrogen receptor regulates embryonic heart rate in zebrafish

Estrogens act by binding to estrogen receptors alpha and beta (ERα, ERβ), ligand-dependent transcription factors that play crucial roles in sex differentiation, tumor growth and cardiovascular physiology. Estrogens also activate the G protein-coupled estrogen receptor (GPER), however the function of GPER in vivo is less well understood. Here we find that GPER is required for normal heart rate in zebrafish embryos. Acute exposure to estrogens increased heart rate in wildtype and in ERα and ERβ mutant embryos but not in GPER mutants. GPER mutant embryos exhibited reduced basal heart rate, while heart rate was normal in ERα and ERβ mutants. We detected gper transcript in discrete regions of the brain and pituitary but not in the heart, suggesting that GPER acts centrally to regulate heart rate. In the pituitary, we observed gper expression in cells that regulate levels of thyroid hormone triiodothyronine (T3), a hormone known to increase heart rate. Compared to wild type, GPER mutants had reduced levels of T3 and estrogens, suggesting pituitary abnormalities. Exposure to exogenous T3, but not estradiol, rescued the reduced heart rate phenotype in gper mutant embryos, demonstrating that T3 acts downstream of GPER to regulate heart rate. Using genetic and mass spectrometry approaches, we find that GPER regulates maternal estrogen levels, which are required for normal embryonic heart rate. Our results demonstrate that estradiol plays a previously unappreciated role in the acute modulation of heart rate during zebrafish embryonic development and suggest that GPER regulates embryonic heart rate by altering maternal estrogen levels and embryonic T3 levels.

Estrogen hormones are important for the formation and function of the nervous, reproductive and cardiovascular systems. Here we report that acute exposure to estrogens increases heart rate, a previously unappreciated function of estrogens. Using zebrafish with mutations in genes that respond to estrogens, we found that heart rate is regulated not by the typical molecules that respond to estrogens–the nuclear estrogen receptors–but rather by a different molecule, the G protein-coupled estrogen receptor. We also show that estrogens increase heart rate by increasing levels of thyroid hormone. Our results reveal a new function for the G protein-coupled estrogen receptor and a new connection between estrogens and thyroid hormone. Environmental compounds that mimic estrogens can be harmful because they can influence gonad function. Our results suggest that endocrine disrupting compounds may also influence cardiac function.

Epigenetics, inflammation and metabolism in right heart failure associated with pulmonary hypertension

Right ventricular failure (RVF) is the most important prognostic factor for both morbidity and mortality in pulmonary arterial hypertension (PAH), but also occurs in numerous other common diseases and conditions, including left ventricle dysfunction. RVF remains understudied compared with left ventricular failure (LVF). However, right and left ventricles have many differences at the morphological level or the embryologic origin, and respond differently to pressure overload. Therefore, knowledge from the left ventricle cannot be extrapolated to the right ventricle. Few studies have focused on the right ventricle and have permitted to increase our knowledge on the right ventricular-specific mechanisms driving decompensation. Here we review basic principles such as mechanisms accounting for right ventricle hypertrophy, dysfunction, and transition toward failure, with a focus on epigenetics, inflammatory, and metabolic processes.

Dysthyroidism and Chronic Heart Failure: Pathophysiological Mechanisms and Therapeutic Approaches

Among comorbidity in chronic heart failure (CHF), dysthyroidism represents a relevant problem especially in the ageing CHF patients worldwide. Thyroid greatly affects many cardiovascular activities and its dysfunction may worsen a CHF condition. In particular, hypothyroidism has a relative high prevalence in patients with heart failure and it plays a key role in influencing CHF onset, progression and prognosis. Hyperthyroidism, is less frequent in this clinical context but it necessitates of immediate treatment because of its negative effects on cardiovascular balance. Also, it must be considered that dysthyroism may also be iatrogenic and the main responsible drug is Amiodarone.Based on the best available evidence and our cumulative clinical experience, this manuscript analyzes the prevalence, the pathophysiology and the prognostic impact of thyroid disorders in chronic heart failure.

The IGF1-PI3K-Akt Signaling Pathway in Mediating Exercise-Induced Cardiac Hypertrophy and Protection

Regular physical activity or exercise training can lead to heart enlargement known as cardiac hypertrophy. Cardiac hypertrophy is broadly defined as an increase in heart mass. In adults, cardiac hypertrophy is often considered a poor prognostic sign because it often progresses to heart failure. Heart enlargement in a setting of cardiac disease is referred to as pathological cardiac hypertrophy and is typically characterized by cell death and depressed cardiac function. By contrast, physiological cardiac hypertrophy, as occurs in response to chronic exercise training (i.e. the 'athlete's heart'), is associated with normal or enhanced cardiac function. The following chapter describes the morphologically distinct types of heart growth, and the key role of the insulin-like growth factor 1 (IGF1) - phosphoinositide 3-kinase (PI3K)-Akt signaling pathway in regulating exercise-induced physiological cardiac hypertrophy and cardiac protection. Finally we summarize therapeutic approaches that target the IGF1-PI3K-Akt signaling pathway which are showing promise in preclinical models of heart disease.

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.

Echocardiographic assessment of left ventricular function in thyrotoxicosis and implications for the therapeutics of thyrotoxic cardiac disease

INTRODUCTION

Thyrotoxicosis is an endocrine disorder with prominent cardiovascular manifestations. Thyroid hormone acts through genomic and non-genomic mechanisms to regulate cardiac function. Echocardiography is a useful, non-invasive, easily accessible, and affordable tool for studying the structural and physiological function of the heart.

AIM

We studied thyrotoxicosis patients in a Nigerian Teaching Hospital and employed trans-thoracic echocardiography to find out if there were abnormalities in the hearts of these patients.

METHODS

Fifty adult thyrotoxicosis patients diagnosed with clinical and thyroid function tests in the medical out-patient unit of the hospital were recruited and we performed transthoracic echocardiography with a Sonos 2000 HP machine.

RESULTS

We documented the presence of abnormalities in the following proportion of thyrotoxicosis patients: left ventricular enhanced systolic function in 30%, enhanced diastolic function in 34%, diastolic dysfunction in 34%, heart failure with preserved ejection fraction in10%, heart failure with reduced ejection fraction in 6%, and left ventricular hypertrophy in 34%.

CONCLUSION

Echocardiography was useful in the stratification of cardiac function abnormalities and is indispensable as a guide in the choice of therapeutic options in patients with thyrocardiac disease. The finding of left ventricular enhanced systolic and diastolic functions signify early echocardiographic detectable cardiac abnormalities in thyrotoxicosis, and the clinical management includes the use of anti-thyroid drugs and β-adrenoceptor blockade. Diastolic dysfunction in thyrotoxicosis patients asymptomatic for cardiac disease should be treated with anti-thyroid drugs, and β-adrenoceptor blockade. The judicious application of clinical therapeutics will guide the use of anti-thyroid drugs, diuretics, digoxin, angiotensin inhibitors, and β-adrenoceptor blockade in the successful management of thyrotoxicosis patients with heart failure and reduced, preserved, or increased ejection fraction: parameters which are derived from echocardiography.

Gene polymorphisms and thyroid function in patients with heart failure

We evaluated nuclear factor kappa B {NFkB, rs28362491 [-94ins/delATTG (W/D)]} and angiotensin converting enzyme {ACE; rs1799752 [Ins(I)/Del(D)]} gene polymorphisms and their correlation with thyroid function in patients with heart failure (HF). Peak oxygen uptake (VO(2)) was evaluated (by Weber classification) during a symptom-limited cardiopulmonary exercise test in 194 patients. Thyroid-stimulating hormone, triiodothyronine (T3), thyroxine (T4), and free (F) T3 and FT4 were also measured. According to their cardiovascular (CV) capacity, patients were subdivided into four groups: group A included patients with peak VO(2) >20 ml/kg/min, group B 16-20 ml/kg/min, group C 10-16 ml/kg/min, and group D 6-10 ml/kg/min. Patients were also genotyped for NFkB and ACE genetic variants. T3 was increased and FT3 was decreased for every raise in Weber's classification (p = 0.007 and p = 0.012, respectively). Del carriers had elevated FT3 levels compared with Ins carriers (p = 0.021). Patients with II genotype had elevated T4 levels compared with ID genotype (p = 0.044). Both T4 and FT4 were decreased in D allele carriers (p = 0.007 and p = 0.045, respectively). Thyroid hormones correlated with CV capacity. Associations between the NFkB and ACE gene polymorphisms and thyroid hormones levels were also observed. Further larger studies are required to clarify genes contribution in HF.

A review of literature on the adverse effects of hyperthyroidism on the heart functional behavior

Thyroid hormones play an important role on the physiological chemistry of heart and vascular systems in healthy subjects. Any thyroid disorders accompanied with alteration of effective concentration of thyroid hormones cause heart dysfunctions. Thyrotoxicosis is a term given for the clinical manifestation of hyperthyroidism which can invoke heart and vascular abnormalities through the mechanism at heart muscle cells nuclear level. Thyrotoxicosis can play positive roles for heart disorders including atrial fibrillation, left ventricular hypertrophy and right ventricular systolic dysfunction, which are considered as major risk factors for heart abnormalities. Miscalculation of heart dysfunctions related thyrotoxicosis in cardiovascular patients might be avoided through careful laboratory measurements of T4 and T3 to exclude any possible thyroid hormone-related heart diseases.

Prevalence of echocardiographic criteria for the diagnosis of pulmonary hypertension in patients with Graves' disease: before and after antithyroid treatment

BACKGROUND

Right-sided heart failure with clinical manifestation is only occasionally seen in patients with Graves' disease (GD). Recent studies revealed that pulmonary hypertension (PHT) detected by echocardiography was not rare in patients with GD. We performed this study to investigate the prevalence of PHT in patients with GD before and after antithyroid treatment, and to assess potential mechanisms from the relationship with clinical and echocardiographic features.

SUBJECTS AND METHODS

Serial echocardiographic examinations were performed in 64 patients with newly diagnosed GD before and after antithyroid treatment to measure cardiac factors, such as pulmonary artery systolic pressure (PAPs), cardiac output, total vascular resistance, left ventricular filling pressure and right ventricular (RV) function. PHT was defined as PAPs of at least 35 mmHg.

RESULTS

The prevalence of PHT in untreated GD patients was 44% (28 out of 64 patients). The presence of systemic hypertension was associated with PHT, especially with pulmonary venous hypertension. GD patients with PHT showed reduced RV function represented by higher RV myocardial performance index without difference of pulmonary vascular resistance, RV wall thickness and peak systolic velocity of free wall side of tricuspid annulus. Follow-up echocardiography was performed in 20 out of 28 GD patients with PHT, and PHT disappeared in all except one patient.

CONCLUSION

PHT is a frequent and reversible complication in patients with GD. Our study suggests that PHT in GD may not be related to underlying autoimmune process and increased pulmonary blood flow from thyrotoxicosis might contributes to the pathogenesis of PHT related to GD.

Hyperthyroidism-induced left ventricular diastolic dysfunction: implication in hyperthyroidism-related heart failure

BACKGROUND

Heart failure occurs in 6% of hyperthyroid patients. Nonetheless, only half of those with hyperthyroidism-related heart failure have impaired left ventricular (LV) systolic function. Thus, diastolic dysfunction may play an important role in the pathogenesis.

METHODS AND RESULTS

We performed serial echocardiographic examinations in 70 consecutive patients with hyperthyroidism (39 ± 2 years, 47 women) to determine their diastolic function and repeated the examinations 6 months after achieving a euthyroid state. All patients had normal LV systolic function, but diastolic dysfunction was detected in 22 cases (mild: 3, moderate: 15 and severe: 4). The prevalence of diastolic dysfunction increased with age from 17·9 % in patients <40 years to 100% in those >60 years. Increasing age was the only independent predictor for diastolic dysfunction in hyperthyroid patients. After achievement of a euthyroid state, most patients (16/22, 72%) had completely normalized diastolic function: 100% of patients <40 years, 33·3 % of those ≥ 60 years. Further analyses revealed significant age-related differences in the cardiovascular response to hyperthyroidism. Among patients <40 years, hyperthyroidism resulted in a marked reduction in total peripheral vascular resistance, increased cardiac output and enhanced diastolic function as determined by E'. No such significant change in total peripheral vascular resistance or cardiac output was observed in hyperthyroid patients ≥ 40 years. In addition, hyperthyroidism was associated with reduced E', signifying diastolic dysfunction in older hyperthyroid patients.

CONCLUSION

Hyperthyroidism is associated with diastolic dysfunction, particularly in older patients. It is partly reversible following achievement of a euthyroid state.

Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies

Cardiac hypertrophy can be defined as an increase in heart mass. Pathological cardiac hypertrophy (heart growth that occurs in settings of disease, e.g. hypertension) is a key risk factor for heart failure. Pathological hypertrophy is associated with increased interstitial fibrosis, cell death and cardiac dysfunction. In contrast, physiological cardiac hypertrophy (heart growth that occurs in response to chronic exercise training, i.e. the 'athlete's heart') is reversible and is characterized by normal cardiac morphology (i.e. no fibrosis or apoptosis) and normal or enhanced cardiac function. Given that there are clear functional, structural, metabolic and molecular differences between pathological and physiological hypertrophy, a key question in cardiovascular medicine is whether mechanisms responsible for enhancing function of the athlete's heart can be exploited to benefit patients with pathological hypertrophy and heart failure. This review summarizes key experimental findings that have contributed to our understanding of pathological and physiological heart growth. In particular, we focus on signaling pathways that play a causal role in the development of pathological and physiological hypertrophy. We discuss molecular mechanisms associated with features of cardiac hypertrophy, including protein synthesis, sarcomeric organization, fibrosis, cell death and energy metabolism and provide a summary of profiling studies that have examined genes, microRNAs and proteins that are differentially expressed in models of pathological and physiological hypertrophy. How gender and sex hormones affect cardiac hypertrophy is also discussed. Finally, we explore how knowledge of molecular mechanisms underlying pathological and physiological hypertrophy may influence therapeutic strategies for the treatment of cardiovascular disease and heart failure.

Thyroid function and left ventricular structure and function in the Framingham Heart Study

BACKGROUND

Thyroid hormone acts on the heart and peripheral vasculature in multiple ways. Even in patients with subclinical hypo- or hyperthyroidism, subclinical alterations in left ventricular (LV) structure and function may be associated with important clinical effects. Our objective was to determine whether thyroid function is related to echocardiographic indices of LV structure and function.

METHODS

Cross-sectional association of serum thyroid-stimulating hormone (TSH) with two-dimensional-guided M-mode echo LV dimensions and function. Participants were 1376 Framingham Heart Study participants (61% women, mean age 69 years) who attended a routine examination 1979-1981. We excluded participants with myocardial infarction or heart failure, renal insufficiency, and missing data, and those using thyroid hormone or antithyroid medications. Serum TSH was measured 1977-1979. The following echocardiographic measurements were analyzed both as continuous variables and dichotomized at the top quintile: LV end-diastolic dimensions, LV wall thickness, LV mass, LV fractional shortening (an indicator of systolic function), and left atrial diameter. Sex-specific multiple regression models were adjusted for age, height, weight, blood pressure, heart rate, total to high-density lipoprotein cholesterol ratio, and the presence of diabetes, hypertension treatment, and valve disease.

RESULTS

In multivariable linear models, log-TSH was not related to LV mass, LV wall thickness, or left atrial size in either sex, or to LV systolic function in men. Log-TSH had a borderline inverse association with fractional shortening (p = 0.06) in women. In multivariable logistic models, women with TSH <0.5 mU/L (n = 81) had a greater odds of being in the highest quintile of fractional shortening compared to euthyroid subjects (odds ratio 2.2, 95% confidence interval 1.3-3.8, p = 0.01).

CONCLUSIONS

In our moderate-sized community-based sample, TSH concentration was not associated with LV structure in either sex, but was inversely related to LV contractility, consistent with the known inotropic effects of thyroid hormone.

QTc dispersion in hyperthyroidism and its association with pulmonary hypertension

BACKGROUND

Several studies have reported that hyperthyroidism is associated with prolonged QT interval corrected by the heart rate (QTc) and pulmonary hypertension (PHT).

METHODS

Forty-seven patients with newly diagnosed overt hyperthyroidism and 20 healthy people were enrolled in the study. Transthoracic echocardiography, 12-lead surface electrocardiogram, and thyroid hormone levels were studied at the time of enrollment and after achievement of euthyroid state with propylthiouracil treatment.

RESULTS

Baseline clinical characteristics were similar. However, heart rate (90.5+/-19.6 vs 79.2+/-13.7 bpm, P = 0.024), pulmonary artery systolic pressure (PASP) (26.0+/-12.0 vs 10.6+/-4.0 mmHg, P < 0.001), E deceleration time (DT) (191.8+/-25.6 vs 177.0+/-10.7 ms, P = 0.016), isovolumetric relaxation time (IVRT) (91.38+/-12.3 vs 79.6+/-10.5 ms, P < 0.001), and QTc dispersion (QTcD) (50.3+/-17.2 vs 38.9+/-11.6 ms, P = 0.009) were significantly higher in hyperthyroid patients compared to control group. Heart rate (to 74.1+/-13.8, P < 0.001), QTcD (to 37.3+/-10.1 ms, P < 0.001), DT (to 185.3+/-19.7 ms, P = 0.008), IVRT (to 88.6+/-10.3 ms, P = 0.056), and PASP (23.1+/-10.1 mmHg P < 0.001) were significantly decreased after achievement of euthyroid state. Although PHT was present in 16 patients before treatment only six patients still had PHT during euyhyroid state. Compared to patients with normal PASP, QTcD was significantly longer in patients with PHT (56.5+/-15.8 vs 37.9+/-12.8 mmHg P < 0.001). There were also significant correlations between QTcD and presence of PHT (r = 0.516, P < 0.001) and PASP (r = 0.401, P = 0.009).

CONCLUSIONS

Hyperthyroidism is a reversible cause of PHT and diastolic dysfunction. Increased QTcD observed in hyperthyroidism may be associated with PHT and diastolic dysfunction. These abnormal findings in hyperthyroidism often normalize with the achievement of euthyroid state.

Incidence, clinical characteristics and outcome of congestive heart failure as the initial presentation in patients with primary hyperthyroidism

BACKGROUND

There are limited systematic data on the incidence, clinical characteristics and outcomes of congestive heart failure (CHF) in patients with hyperthyroidism. The aim of this study was to investigate the incidence, clinical characteristics and outcome of CHF as the initial presentation in patients with primary hyperthyroidism.

METHODS

The prevalence, clinical characteristics and outcome of CHF was studied in 591 consecutive patients (mean (SD) age 45 (1) years, 140 men) who presented with primary hyperthyroidism.

RESULTS

CHF was the presenting condition in 34 patients (5.8%) with hyperthyroidism. The presence of atrial fibrillation at presentation (OR 37.4, 95% CI 9.72 to 144.0, p<0.001) was an independent predictor for the occurrence of CHF. Of the 34 patients with CHF, 16 (47%) had systolic left ventricular dysfunction with left ventricular ejection fraction (LVEF)<50%. They were predominantly male (OR 26.6, 95% CI 2.6 to 272.5, p = 0.006) and had a lower serum thyroxine level (OR 0.93, 95% CI 0.87 to 0.99, p = 0.044) than patients with preserved left ventricular systolic function. In these patients, LVEF (55 (4)% vs 30 (2)%, p<0.001) and New York Heart Association functional class (1.2 (0.1) vs 2.5 (0.2), p<0.001) improved significantly 3 months after achieving euthyroid status. Systolic left ventricular dysfunction (mean (SD) LVEF 38 (4)%) persisted on long-term follow-up in five

PATIENTS

no clinical parameter could be identified to predict the occurrence of this persistent cardiomyopathy (p>0.05).

CONCLUSION

CHF was the initial clinical presentation in approximately 6% of patients with hyperthyroidism, and half of them had left ventricular systolic dysfunction. Symptoms of CHF subsided and LVEF improved after treatment for hyperthyroidism. Nonetheless, one-third of these patients developed persistent dilated cardiomyopathy.

Thyroid hormone stimulates protein synthesis in the cardiomyocyte by activating the Akt-mTOR and p70S6K pathways

Thyroid hormones affect cardiac growth and phenotype; however, the mechanisms by which the hormones induce cardiomyocyte hypertrophy remain uncharacterized. Tri-iodo-L-thyronine (T3) treatment of cultured cardiomyocytes for 24 h resulted in a 41 +/- 5% (p < 0.001) increase in [(3)H]leucine incorporation into total cellular protein. This response was abrogated by the phosphatidylinositol 3-kinase (PI3K) inhibitor, wortmannin. Co-immunoprecipitation studies showed a direct interaction of cytosol-localized thyroid hormone receptor TRalpha1 and the p85alpha subunit of PI3K. T3 treatment rapidly increased PI3K activity by 52 +/- 3% (p < 0.005), which resulted in increased phosphorylation of downstream kinases Akt and mammalian target of rapamycin (mTOR). This effect was abrogated by pretreatment with wortmannin or LY294002. Phosphorylation of p70(S6K), a known target of mTOR, occurred rapidly following T3 treatment and was inhibited by rapamycin and wortmannin. In contrast, phosphorylation of the p85 variant of S6K in response to T3 was not blocked by LY294002, wortmannin, or rapamycin, thus supporting a T3-activated pathway independent of PI3K and mTOR. 40 S ribosomal protein S6, a target of p70(S6K), and 4E-BP1, a target of mTOR, were both phosphorylated within 15-25 min of T3 treatment and could be inhibited by wortmannin and rapamycin. Thus, rapid T3-mediated activation of PI3K by cytosolic TRalpha1 and subsequent activation of the Akt-mTOR-S6K signaling pathway may underlie one of the mechanisms by which thyroid hormone regulates physiological cardiac growth.

Répercussions cardiaques des dysthyroïdies avérées

KEY POINTS

Thyroid hormones affect the vascular system, including the diastolic and systolic functioning of the heart. Resting heart rate increases early in hyperthyroidism (cardiac contractility expands due to improved ventricular loading and decreased systemic vascular resistance). Paradoxically, these hemodynamic alterations progressively reduce cardiac performance on effort (changes in diastolic, then systolic functioning) and finally at rest (modification in ventricular loading following tachycardia or atrial fibrillation), especially in cases of underlying heart disease (in the elderly). Hypothyroidism has an inverse hemodynamic effect and is less noisy, usually limited to relative bradycardia. The morbidity and mortality associated with hypothyroidism are apparently related to the atherogenic and prothrombotic vascular modifications that follow thyroid hormone deficiency, whereas heart failure and particularly atrial fibrillation and its thromboembolic complications are the primary consequences of hyperthyroidism. In both cases, return to normal thyroid levels corrects the cardiac abnormalities caused by the dysthyroidism. Dysthyroidism (hypo- or hyperthyroidism) occurs in 10 to 20% of the patients treated with amiodarone for arrhythmia. Because of its potential seriousness, some clinical or laboratory tests are necessary before initiating treatment, and specific clinical surveillance should be scheduled, including laboratory tests.

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

OBJECTIVES

We sought to assess the effects of subclinical hypothyroidism (SHT) on the cardiac volumes and function.

BACKGROUND

The cardiovascular system is one of the principal targets of thyroid hormones. Subclinical hypothyroidism is a common disorder that may represent "early" thyroid failure.

METHODS

Thyroid profile was evaluated in 30 females with SHT and 20 matched control subjects. Left ventricular end-diastolic volume (EDV) and end-systolic volume (ESV), stroke volume (SV), cardiac index (CI), and systemic vascular resistance (SVR) were calculated by cardiac magnetic resonance (CMR). Regional greatest systolic lengthening (E1) and greatest systolic shortening (E2) were calculated by tagging CMR.

RESULTS

EDV was lower in SHT than in controls (64.3 +/- 8.7 ml/m(2) vs. 81.4 +/- 11.3 ml/m(2), p < 0.001), as well as SV [corrected] (38.9 +/- 7.5 ml/m(2) vs. 52.5 +/- 6.1 ml/m(2), p < 0.001) and CI (2.6 +/- 0.5 l/[min.m(2)] vs. 3.7 +/- 0.4 l/[min.m(2)], p < 0.001). SVR [corrected] was higher in SHT (12.5 +/- 2.5 mm Hg.min/[l.m(2)] vs. 8.6 +/- 1.1 mm Hg.min/[l.m(2)], p = 0.003). The E1 was higher in controls than in SHT at the basal (p = 0.007), equatorial (p = 0.05), and apical (p = 0.008) levels, as well as E2 at the equatorial (p = 0.001) and apical (p = 0.001) levels. All parameters normalized after replacement therapy. A negative correlation between TSH and EDV (p < 0.001), SV (p < 0.001), CI (p < 0.001), and E1 at the apical level (p < 0.001) and a positive correlation between TSH and SVR (p < 0.001) and E2 at the apical level (p < 0.001) were found.

CONCLUSIONS

Subclinical hypothyroidism significantly decreased cardiac preload, whereas it increased afterload with a consequent reduction in SV and cardiac output. Replacement therapy fully normalized the hemodynamic alterations.

Genomic and non-genomic regulation of L-type calcium channels in rat ventricle by thyroid hormone

Hyperthyroidism is associated with low exercise tolerance despite high cardiac output and sometimes with the development of heart failure. L-type calcium channels may play a role in the mechanism, but this has not been fully understood. We examined the effects of thyroid hormone on gene expression and function of L-type calcium channels in rat ventricles by the ribonuclease protection assay and whole-cell patch-clamp technique, respectively. The effects of bisoprolol, beta-blocking agent, on the regulation of calcium channel by thyroid hormone was also studied. In hyperthyroid animals, the mRNA of the calcium channel alpha1c subunit was reduced on day 4, compared with that in euthyroid animals, and remained low on day 8. Bisoprolol did not affect the thyroid hormone mediated decrease in alpha1c subunit mRNA. While L-type calcium current was greater in hyperthyroid than euthyroid myocytes on day 4, it was smaller on day 8. In addition, the isoproterenol-induced increase in calcium current in euthyroid rats was attenuated in hyperthyroid rats. Acetylcholine decreased calcium current in hyperthyroid myocytes, but not in euthyroid myocytes. In conclusion, L-type calcium current was increased by thyroid hormone in rat ventricular myocytes by the activation of the adenylate cyclase cascade, despite a decreased calcium channel gene expression. These genomic and non-genomic modifications may play an important role in the association of high cardiac output with low exercise tolerance, and in the development of heart failure in hyperthyroidism.

Spironolactone prevents cardiac collagen proliferation after myocardial infarction in rats

1. Aldosterone has been considered a key hormone in the regulation of water, sodium and potassium metabolism, thus influencing blood pressure regulation. More recently, several studies have demonstrated that aldosterone is also produced in extra-adrenal tissues (e.g. the heart), suggesting a paracrine effect for aldosterone, such as to increase collagen synthesis in the heart. 2. Because aldosterone production in the heart increases after myocardial infarction (MI), we investigated the effect of chronic administration of spironolactone, an aldosterone receptor antagonist, in rats after MI compared with the effects produced by losartan and hydralazine. 3. Myocardial infarction was produced in male Wistar rats by surgical ligature of the left coronary artery. Sham-operated animals were used as controls. 4. Spironolactone (20 mg/kg per day), losartan (15 mg/kg per day) or hydralazine (20 microg/kg per day) were administered after MI and used for 1 month. 5. At the end of the treatment period, animals underwent haemodynamic recording (arterial and intraventricular pressures). The collagen content of the heart was evaluated by measuring the hydroxyproline (OH-Pro) concentration in right (RV) and left ventricle (LV) muscle fragments. 6. Infarct size was unaffected by drug treatments. The increased LV end-diastolic pressure observed in MI rats was prevented by losartan and remained unchanged following administration of spironolactone or hydralazine. 7. Losartan prevented RV and LV hypertrophy, as well as collagen proliferation in both ventricles, after MI. The postinfarction hypertrophy observed in RV and LV after MI remained unchanged in infarcted groups treated with spironolactone or hydralazine. 8. The OH-Pro concentration was significantly reduced in LV muscle in the MI group treated with spironolactone (682 +/- 40 vs 557 +/- 21 microg/g for MI vs MI + spironolactone, respectively; P < 0.05), an effect not observed in the hydralazine-treated group. 9. These data suggest that spironolactone prevents collagen proliferation in the surviving myocardium by mechanisms independent of the loading conditions of the heart chambers. Control of postinfarction hypertrophy and collagen accumulation produced by losartan seems to depend on the reduction in loading conditions of the heart chambers.

Thyroid hormone and cardiac function in mice deficient in thyroid hormone receptor-alpha or -beta: an echocardiograph study

We investigated the effect of thyroid hormone (TH) receptor (TR)alpha and -beta isoforms in TH action in the heart. Noninvasive echocardiographic measurements were made in mice homozygous for disruption of TRalpha (TRalpha(0/0)) or TRbeta (TRbeta(-/-)). Mice were studied at baseline, 4 wk after TH deprivation (using a low-iodine diet containing propylthiouracil), and after 4-wk treatment with TH. Baseline heart rates (HR) were similar in wild-type (WT) and TRalpha(0/0) mice but were greater in TRbeta(-/-) mice. With TH deprivation, HR decreased 49% in WT and 37% in TRbeta(-/-) mice and decreased only 5% in TRalpha(0/0) mice from baseline, whereas HR increased in all genotypes with TH treatment. Cardiac output (CO) and cardiac index (CI) in WT mice decreased (-31 and -32%, respectively) with TH deprivation and increased (+69 and +35%, respectively) with TH treatment. The effects of CO and CI were blunted with TH withdrawal in both TRalpha(0/0) (+8 and -2%, respectively) and TRbeta(-/-) mice (-17 and -18%, respectively). Treatment with TH resulted in a 64% increase in LV mass in WT and a 44% increase in TRalpha(0/0) mice but only a 6% increase in TRbeta(-/-) mice (ANOVA P < 0.05). Taken together, these data suggest that TRalpha and TRbeta play different roles in the physiology of TH action on the heart.

Cellular action of thyroid hormone on the heart

Changes in thyroid status markedly influence cardiac contractile and electrical activity. The predominant route by which triiodothyronine (T3) affects cardiac action is by exerting a direct effect in cardiac myocytes through binding to thyroid hormone nuclear receptor isoforms. In addition, T3 modifies cardiac action by alterations in the vascular system and decreases afterload of the left ventricle by subtle modification related to the sympathetic system. The importance of T3 nuclear receptor function has been further demonstrated by studies in null mutant mice in which thyroid hormone receptor-alpha (TRalpha) and thyroid hormone receptor-beta (TRbeta) or both are deleted. In mice with null mutations of the TRalpha, a markedly decreased heart rate and decreased contractile performance occurs in contrast to mice with deletion of TRbeta that have a normal heart rate and a normal contractile performance under baseline conditions. Thyroid hormone influences on heart rate are exerted by specific ion channel proteins in the sinus node of the left atrium. Some of these ion channels, such as the IF channel, the sodium/calcium exchanger protein, the L-type and T-type calcium channel, and the ryanodine channel are targets for thyroid hormone action. The increased contractile performance induced by T3 is largely mediated by increased expression of the calcium adenosine triphosphatase (ATPase) of the sarcoplasmic reticulum and decreased expression of phospholamban and T3 increases the phosphorylation status of phospholamban. The significant influence that is exerted by thyroid hormone signaling system related to contractile and electrical activity in the heart and the molecular basis for these alterations continues to be clarified.

Hyperthyroidism and cardiovascular morbidity and mortality

Hyperthyroidism is a common disorder affecting multiple systems in the body. The cardiovascular effects are among the most striking. The availability of effective treatments for hyperthyroidism has led to the widespread perception that it is a reversible disorder without any long-term consequences. Recent evidence suggests, however, that there may be adverse outcomes. Long-term follow-up studies have revealed increased mortality from cardiovascular and cerebrovascular disease in those with a past history of overt hyperthyroidism treated with radioiodine, as well as those with subclinical hyperthyroidism. Thyroid hormones are known to exert direct effects on the myocardium, as well as the systemic vasculature and predispose to dysrhythmias, especially supraventricular. Atrial fibrillation (AF) is a recognized complication of overt hyperthyroidism, and subclinical hyperthyroidism is also known to be a risk factor for development of AF. Supraventricular dysrhythmias, particularly atrial fibrillation, in older patients may account for some of the excess cardiovascular and cerebrovascular mortality described, especially because AF is known to predispose to embolic phenomena.

Stress echocardiography in hyperthyroidism

Exertion symptoms occur frequently in subjects with hyperthyroidism. Using stress echocardiography, exercise capacity and global left ventricular function can be assessed noninvasively. To evaluate stress-induced changes in cardiovascular function, 42 patients with untreated thyrotoxicosis were examined using exercise echocardiography. Studies were performed during hyperthyroidism, after treatment with propranolol, and after restoration of euthyroidism. Twenty-two healthy subjects served as controls. Ergometry was performed with patients in a semisupine position using a continuous ramp protocol starting at 20 watts/min. In contrast to control and euthyroidism, the change in end-systolic volume index from rest to maximal exercise was lower in hyperthyroidism. At rest, the stroke volume index, ejection fraction, and cardiac index were significantly increased in hyperthyroidism, but exhibited a blunted response to exercise, which normalized after restoration of euthyroidism. Propranolol treatment also led to a significant increase of delta (delta) stroke volume index. Maximal work load and delta heart rate were markedly lower in hyper- vs. euthyroidism. Compared to the control value, systemic vascular resistance was lowered by 36% in hyperthyroidism at rest, but no further decline was noted at maximal exercise. The delta stroke volume index, delta ejection fraction, delta heart rate, and maximal work load were significantly reduced in severe hyperthyroidism. Negative correlations between free T3 and diastolic blood pressure, maximal work load, delta heart rate, and delta ejection fraction were noted. Thus, in hyperthyroidism, stress echocardiography revealed impaired chronotropic, contractile, and vasodilatatory cardiovascular reserves, which were reversible when euthyroidism was restored.

[Angina pectoris in extracoronary diseases]

Chest pain can arise from cardiovascular or noncardiovascular causes. Among the latter are the skin, the chest wall, intrathoracic structures, or subdiaphragmatic organs. The problem to attribute the chest discomfort to either the heart or extracardiac organs arises because the heart, pleura, aorta, and esophagus are all supplied by sensory fibers from the same spinal segments. In contrast to the diseases mentioned above, angina pectoris in sensu strictu is defined as chest pain or discomfort of cardiac origin that arises because of temporary imbalance between myocardial oxygen supply and demand. The metabolic oxygen requirements of the myocardium are essentially dictated by myocardial contraction since only a fraction of the consumed oxygen is needed by the quiescent heart. Therefore, the factors that primarily influence myocardial oxygen consumption include heart rate, the force of cardiac contraction, and myocardial wall tension, as determined by pressure (afterload), volume (preload), and wall thickness. Extracoronary diseases, e.g. hypertensive heart disease, aortic stenosis or cardiomyopathies, can influence these factors and induce angina pectoris (Figure 1). On the other hand, different diseases influencing the oxygen supply, e.g. anemia, can cause angina pectoris, too. In addition, the modulation of the coronary tone by mediators and cytokines can cause angina, coronary spasm being one example. The neurophysiological substrate of angina pectoris are ganglia which are present within the heart, particularly in epicardial fat. The sympathetic nervous system is the main conveyer of afferent pain fibers from the heart and pericardium, but many fibers may travel by the vagus and the phrenic nerves. Therefore, multiple thoracic structures may cause similar pain syndromes in the distressed patient. The blood supply of intrinsic cardiac ganglia arises primarily from branches of the proximal coronary arteries. Adenosine, among a number of substances, can modulate the activity generated by cardiac afferent nerve endings and intrinsic cardiac neurones. During myocardial ischemia adenosine is released in large quantities into the interstitial space. Given as an intravenous bolus to healthy volunteers or to patients with ischemic heart disease and angina pectoris, adenosine provokes angina pectoris-like pain, which is similar to habitual angina pectoris with regard to quality and location. But other mediators (e.g. bradykinin, histamine, prostaglandins, potassium, lactate) can be involved in the development of angina pectoris, too. As most emphasis should be given to the most serious causes first, the cardiologist has to consider ischemic cardiac disease in the differential diagnosis of nearly every case of acute chest pain. The differential diagnosis contains several causes of nonischemic cardiac chest pain. Dissecting aortic aneurysm may cause severe anterior chest pain that can be mistaken for myocardial infarction. Patients frequently will note the sudden onset of the pain rather than the relatively slower onset of ischemic pain. Furthermore, they feel as a tear and describe it as the most severe pain they have ever had. Pericarditis can be characterized as a sharp precordial knife-like pain that is often increased by lying down, breathing, swallowing, or any other thoracic motion. Radiation of pericardial pain is often relieved by sitting up or leaning forward. It may involve the shoulders, upper back, and neck because of the irritation of the diaphragmatic pleura. Acute pulmonary embolism is associated with severe chest pain. It may mimic acute myocardial infarction. Pulmonary embolism should be suspected when dyspnea or tachypnea seems to be disproportionate to the severity of the chest pain. Diffuse esophageal spasm is the extracardiac condition that is confused most often with ischemic cardiac chest pain. This pain presents as a deep thoracic pain that may be present over most of the thorax. It may extend down the anterome

Evaluation of ventricular and arterial hemodynamics in anesthetized closed-chest mice

Transgenic and knock-out mice with cardiovascular phenotypes have created the need for methods to measure murine arterial and ventricular mechanics. The aims of this study were (1) to develop a method for the assessment of wall stress (sigma es)-rate corrected velocity of fiber shortening (Vcfc) relation and (2) to assess the feasibility of quantifying global arterial function in normal mice. This method can thus serve as a reference for future studies in genetically altered mice by establishing normal values for comparison. Ten anesthetized closed-chest mice were studied with targeted M-mode echocardiography of the left ventricle recorded simultaneously with high-fidelity aortic pressures. Data were acquired at baseline and during infusions of methoxamine and isoproterenol. Tracings were digitized to obtain end-systolic wall stress (sigma es) and rate-corrected velocity of fiber shortening (Vcfc) relationships and plots of systolic meridional wall stress. Instantaneous aortic pressures and continuous wave aortic Doppler velocities were digitized to study arterial hemodynamics. The Vcfc-sigma es relationship was inverse and linear in all mice studied with a median value of r2 = 0.94. Isoproterenol resulted in an upward shift from the baseline contractility line obtained with methoxamine (mean shift = 2.0 +/- 0.3 circ/sec). Relative to baseline the integral of wall stress decreased with isoproterenol and increased with methoxamine. Methoxamine increased mean arterial pressure and total vascular resistance and decreased heart rate, cardiac output, and arterial compliance. Isoproterenol decreased total vascular resistance and increased cardiac output. Stress-shortening relationships, systolic wall stress, and evaluation of vascular function can be obtained in a closed-chest mouse model.

Mechanics of left ventricular systolic and diastolic function in physiologic hypertrophy of the athlete's heart

As a result of a number of factors, there is tremendous diversity in the pattern of cardiac mechanics encountered in athletes. Nevertheless, several trends can be identified, and several conclusions are possible. Hypertrophy of a mild to moderate degree and out of proportion to body size is a common finding. Some athletes experience ventricular dilation with appropriate hypertrophy and preservation of the ventricular mass-to-volume ratio, whereas others manifest concentric hypertrophy with an increased mass-to-volume ratio. The functional changes that are encountered appear to be secondary to the structural alterations, and there is no evidence of altered myocardial systolic or diastolic properties. Some athletes with hypertrophy have reduced wall stress when they are evaluated at rest, and velocity of shortening is augmented because of the reduced afterload. As a result of adaptation to a high-output state, some athletes appear preload reduced when evaluated at rest. Although velocity of shortening is not affected by preload status, fractional shortening is inversely related to preload. The magnitude of systolic shortening is therefore the net result of altered preload and afterload and cannot be understood without assessing both of these parameters. When the various determinants of systolic shortening are included, contractility appears to be normal. There have been several reports of depressed contractility immediately after extreme exertion. Although the mechanism remains uncertain, several intriguing possibilities have been proposed.

Case report: reversible systolic heart failure and deep jaundice in hyperthyroidism

Systolic heart failure because of hyperthyroidism in patients without preexisting heart disease is not common. Thyrotoxic systolic heart failure is rarely diagnosed during life. Reports about thyrotoxicosis-related systolic heart failure have been diagnosed postmortem. However, antemortem diagnosis of this fatal disease has important clinical implications because if detected early, thyrotoxicosis-related systolic heart failure is reversible. Here is a report a patient with Graves' disease, systolic heart failure, and deep jaundice, which resolved after the treatment of antithyroid drugs.

Triiodothyronine induces over-expression of alpha-smooth muscle actin, restricts myofibrillar expansion and is permissive for the action of basic fibroblast growth factor and insulin-like growth factor I in adult rat cardiomyocytes

Effects of triiodothyronine (T3) on the expression of cytoskeletal and myofibrillar proteins in adult rat cardiomyocytes (ARC) were followed during two weeks of culture in the presence of 20% T3-depleted (stripped) FCS. Control cultures expressed mainly beta-myosin heavy chain (MHC) mRNA. T3 caused a switch to alpha-MHC expression and a dose-dependent increase of alpha-smooth muscle (alpha-sm) actin mRNA and protein. In parallel, the number of alpha-sm actin immunoreactive cells increased from 1% in controls to 29 and 62% in ARC treated with 5 and 100 nM T3. In the presence of T3, cells exhibited a higher beating rate than controls. The distribution of myofibrils in T3-treated cells was restricted to the perinuclear area with a sharp boundary. Only 5% of the control cells but 30 and 62% of the T3-treated (5 and 100 nM) ARC showed this restricted myofibrillar phenotype. Basic fibroblast growth factor (bFGF) which restricts myofibrillar growth and upregulates alpha-sm actin in ARC cultured with normal FCS had no effect on alpha-sm actin in ARC cultured in stripped FCS, but potentiated the effect of T3. In contrast, insulin-like growth factor I (IGF I), which suppresses alpha-sm actin and stimulates myofibrillogenesis in the presence of normal FCS suppressed T3-induced alpha-sm actin expression in stripped FCS. Thus, T3 appears to be permissive for the action of bFGF and IGF I on alpha-sm actin expression.

Cardiac hypertrophy as a result of long-term thyroxine therapy and thyrotoxicosis

OBJECTIVES

To define the effects of long-term thyroxine treatment upon heart rate, blood pressure, left ventricular systolic function, and left ventricular size, as well as indices of autonomic function, and to compare findings with those in patients with thyrotoxicosis before and during treatment.

DESIGN

Cross sectional study of patients prescribed thyroxine long term (n = 11), patients with thyrotoxicosis studied at presentation (n = 23), compared with controls (n = 25); longitudinal study of patients with thyrotoxicosis studied at presentation and serially after beginning antithyroid drug treatment (n = 23).

METHODS

24 h ambulatory monitoring of pulse and blood pressure, echocardiography, forearm plethysmography, and autonomic function tests.

RESULTS

Long-term thyroxine treatment in doses that reduced serum thyrotrophin to below normal had no effect on blood pressure, heart rate, left ventricular systolic function or stroke volume index, but was associated with an 18.4% increase in left ventricular mass index (mean (SEM) 101.9 (3.09) g/m2 v controls 86.1 (4.61), P < 0.01). Thryoxine treatment, like thyrotoxicosis, had no effect on tests of autonomic function. Untreated thyrotoxicosis resulted in pronounced changes in systolic and diastolic blood pressure and an increase in heart rate during waking and sleep. Patients with thyrotoxicosis at presentation had an increase in left ventricular systolic function (ejection fraction 70.5 (1.66)% v 65.4 (1.79), P < 0.01; fractional shortening 40.4 (1.54)% v 35.6 (1.46), P < 0.01), increased stroke volume index (45.9 (2.4) ml/m2 v 36.6 (1.7), P < 0.001), and an increase in forearm blood flow, and decrease in vascular resistance. They had a similar degree of left ventricular hypertrophy to that associated with thyroxine treatment (99.3 (4.03) g/m2); all changes were corrected within 2 months by antithyroid drugs.

CONCLUSIONS

The development of left ventricular hypertrophy in patients receiving thyroxine in the absence of significant changes in heart rate, blood pressure, and left ventricular systolic function is consistent with a direct trophic effect of thyroid hormone on the myocardium. The presence of left ventricular hypertrophy determines that further studies are essential to assess cardiovascular risk in patients taking thyroxine long term.

Thyroid disease: effects on cardiovascular function

Thyroid hormones exert direct effects upon the heart and indirect influences mediated via changes in cardiac work. Overt thyroid dysfunction is frequently associated with cardiovascular symptoms and signs and less frequently with significant cardiovascular morbidity due to atrial fibrillation or cardiac failure. Whether subclinical thyroid dysfunction is similarly associated with adverse effects upon the cardiovascular system remains unclear.

Factitious hyperthyroidism causing acute myocardial infarction

Myocardial ischemia is a rare but severe and possibly life threatening manifestation of hyperthyroidism, but does not usually result in persistent ischemia. We report on a 71-year-old woman who had undergone total thyroidectomy with subsequent irradiation because of follicular carcinoma 3 years ago. Since then, she had been maintained on oral levothyroxine replacement therapy at a dose of 0.15 mg alternating with 0.2 mg daily. When latent hypothyroidism became evident despite replacement therapy, the dose of levothyroxine was increased to 0.3 mg a day. Three weeks later, the patient suffered from an acute posterior myocardial infarction, although she had no previous history of coronary artery disease. Subsequent coronary arteriograms revealed no evidence of disease of the major vessels. Myocardial scintigraphy 3 weeks after infarction still revealed a persistent perfusion defect. Since it is known that thyroid hormones increase oxygen demand, the rapid elevation of oxygen utilization caused by thyrotoxicosis factitia is likely to be responsible for this patient's myocardial infarction. The case illustrates that a sudden increase in levothyroxine replacement dose should be avoided.

Pretreatment with 3,5,3'triiodo-L-thyronine (T3). Effects on myocyte contractile function after hypothermic cardioplegic arrest and rewarming

Circulating levels of 3,5,3'triiodo-L-thyronine are depressed after cardiopulmonary bypass and have been implicated to play a contributory role in the alterations in left ventricular function after hypothermic cardioplegic arrest and rewarming. The central hypothesis of the present study was that pretreatment of isolated myocytes with triiodothyronine will have a direct and beneficial effect on contractile performance after hypothermic cardioplegic arrest and rewarming. Contractile function in isolated pig left ventricular myocytes was examined by video microscopy after the following treatment protocols: (1) 37 degrees C incubation in medium (normothermia) for 2 hours with triiodothyronine followed by a 2-hour normothermic incubation with no triiodothyronine, (2) 4 hours of normothermic incubation with no triiodothyronine, (3) normothermic incubation for 2 hours with triiodothyronine followed by 2 hours of hyperkalemic, hypothermic cardioplegic arrest ([K+]:24 mmol/L; 4 degrees C) and subsequent rewarming, and (4) normothermic incubation for 2 hours with no triiodothyronine followed by 2 hours of hyperkalemic, hypothermic cardioplegic arrest and rewarming. Two hours of normothermia with triiodothyronine increased myocyte contractile function by 30% compared with values in untreated control myocytes, and this increase persisted after a subsequent 2-hour incubation under normothermic conditions with no triiodothyronine. For example, myocyte velocity of shortening in triiodothyronine-pretreated myocytes was 84 +/- 4.9 microns/sec compared with 62 +/- 2.8 microns/sec in control myocytes (p < 0.05). Cardioplegic arrest and subsequent rewarming caused a significant reduction in myocyte velocity of shortening from normothermic values (37 +/- 3.4 microns/sec, p < 0.05). However, in myocytes pretreated with triiodothyronine, myocyte contractile function was significantly higher after hypothermic cardioplegic arrest and rewarming (54 +/- 2.5 microns/sec, p < 0.05). In a second series of experiments, beta-adrenergic responsiveness was examined after pretreatment with triiodothyronine. In the presence of the beta-adrenergic agonist isoproterenol (25 nmol/L), myocyte contractile function was increased by 26% in the triiodothyronine-treated myocytes compared with that in untreated control myocytes. This enhanced beta-adrenergic responsiveness with triiodothyronine pretreatment persisted with subsequent exposure to hypothermic cardioplegic arrest and rewarming. In summary, triiodothyronine pretreatment caused an increase in myocyte contractile function and beta-adrenergic responsiveness under normothermic conditions and after hypothermic cardioplegic arrest and rewarming. Thus the present study provides direct evidence to suggest that preemptive treatment with triiodothyronine may improve left ventricular contractile performance after hypothermic cardioplegic arrest and rewarming.

Thyroid-induced changes in the growth of the liver, kidney, and diaphragm of neonatal rats

Eu-, hypo- and hyper-thyroid rats were studied 12 days postpartum. Hypothyroidism was induced by administering propylthiouracil (PTU) via the mother's drinking water between late gestation and throughout lactation. This procedure effectively blocked the normal early postnatal surge of T3 and T4. In contrast, hyperthyroidism was induced in the young pups by daily injections of T4 from day 3 postpartum. The effects of these experimental manipulations of thyroid status on the rates of protein turnover and growth of the liver, kidney, and diaphragm were studied and compared with measurements made on appropriate euthyroid control tissues. Tissue rates of protein synthesis were decreased in response to hypothyroidism with consequent growth retardation of all three tissues and the whole animal. In contrast, the three body tissues responded very differently to the induction of hyperthyroidism. Hepatic rates of protein synthesis and growth were completely unaffected by thyroid excess. The response of the diaphragm was essentially the reverse of that seen with hypothyroidism, i.e., the enhanced rates of protein synthesis and protein degradation leading to muscle hypertrophy. The rates of protein turnover in the kidney were also increased, but unlike the diaphragm the net result was renal atrophy. Clearly, thyroid hormones influence the normal rapid growth of the neonate and its individual tissues. However, beyond a certain concentration the threshold of responsiveness to these hormones seems to vary between individual tissues.

Non-invasive estimates of aortic root pressures: external subclavian arterial pulse tracing calibrated by oscillometrically determined brachial arterial pressures

This investigation assessed the ability of a non-invasive method to reproduce aortic root pressure waveform and pressures. An external pulse tracing of the subclavian artery was obtained simultaneously with direct aortic root pressures during routine left heart catheterization in 26 patients (aged 39-74 years) with various cardiovascular disorders. Indirect brachial arterial peak-systolic and nadir-diastolic pressures were obtained with oscillometry. The direct and indirect peak-systolic and nadir-diastolic pressures, were separately used to calibrate the pulse tracing. Adequate pulse tracing was obtained in 19 patients (73%). The waveforms agreed well with cross-correlation coefficients for systole and diastole of 0.98. The difference between the pulse trace and the direct pressure curve, when the first was calibrated with the peak-systolic and nadir-diastolic pressures of the latter on average was less than 1 mmHg for systole and diastole. At end-systole the mean difference was 5 mmHg. Oscillometric brachial arterial peak-systolic pressures were (mean +/- SD) 3 +/- 7 mmHg below the corresponding direct measurements, while diastolic pressures were 8 +/- 4 mmHg above. The difference between the pulse trace and the direct pressure curve, when the pulse trace was calibrated with oscillometric pressures, was at end-systole 6 +/- 6 mmHg and for mean arterial pressures 5 +/- 4 mmHg. Thus, the external subclavian arterial pulse tracing provides a non-invasive, clinically feasible access to the aortic root pressure waveform. With optimal calibration, good estimates of aortic root pressures throughout systole and diastole can be obtained, while end-systolic pressure tends to be slightly overestimated.

Effects of triiodothyronine supplementation after myocardial ischemia

Cardiopulmonary bypass causes a "euthyroid-sick" state characterized by low levels of circulating triiodothyronine. Triiodothyronine supplementation in this setting has been postulated to improve postischemic left ventricular function by increasing the availability of myocardial high-energy phosphates. These postulates have not been substantiated, however, using load-independent parameters of left ventricular function and analysis of high-energy phosphate metabolism. To test these hypotheses, 14 healthy pigs (30 to 40 kg) were placed on cardiopulmonary bypass and instrumented with left ventricular minor-axis ultrasonic crystals and micromanometer-tipped pressure catheters. Hearts were subjected to 30 minutes of global, normothermic ischemia. Triiodothyronine (0.1 mg/kg; n = 7) or placebo (n = 7) was administered in a random, investigator-blinded fashion at the removal of the aortic cross-clamp and after 60 minutes of reperfusion. Hemodynamic, metabolic, and ultrastructural data were obtained before ischemia and after 30, 60, 90, and 120 minutes of reperfusion. By 90 minutes of reperfusion left ventricular contractility had returned to preischemic levels in hearts supplemented with triiodothyronine, despite postischemic myocardial adenosine triphosphate levels of 50% to 60% of baseline in both groups. Ultrastructurally, the sarcoplasmic reticulum and mitochondria were significantly better preserved in the group treated with triiodothyronine. This study suggests that triiodothyronine supplementation significantly enhances postischemic left ventricular functional recovery and that this recovery is due to mechanisms other than enhanced availability of myocardial high-energy phosphates.

The thyroid and the heart

Cardiovascular manifestations are a frequent finding in hyperthyroid and hypothyroid states. In this review, potential mechanisms by which thyroid hormones may exert their cardiovascular effects and pathophysiological consequences of such effects are briefly discussed. Two major concepts have emerged about how thyroid hormones exert their cardiovascular effects. First, there is increasing evidence that thyroid hormones exert direct effects on the myocardium, which are mediated by stimulation of specific nuclear receptors, which in turn leads to specific mRNAs production. Furthermore, there is some evidence that thyroid hormones may also activate extranuclear sites and may directly alter plasma membrane function. Second, thyroid hormones interact with the sympathetic nervous system by altering responsiveness to sympathetic stimulation presumably by modulating adrenergic receptor function and/or density. Pathophysiological consequences of such direct and indirect thyroid hormone effects include increased myocardial contractility and relaxation that may be related to stimulation by T3 of specific myocardial enzymes. However, when left ventricular hypertrophy occurs in association with hyperthyroidism, it may be related to either direct thyroid hormone-induced stimulation of myocardial protein synthesis or to thyrotoxicosis-induced increases in cardiac work load. Although hyperthyroidism generally has little or no effect on mean arterial blood pressure, hypothyroidism is often associated with increases in diastolic blood pressure that are reversible after hormone substitution and may be mediated in part by sympathetic activation. Moreover, there is increasing evidence that thyroid hormones have direct chronotropic effect on the heart that are independent of the sympathetic nervous system.(ABSTRACT TRUNCATED AT 250 WORDS)

Triiodothyronine (T3) and cardiovascular therapeutics: a review

Hypothyroidism is associated with an abnormal hemodynamic state characterized by decreased heart rate, stroke volume, output, and contractility, and increased systemic vascular resistance. Since cardiopulmonary bypass (CPB) and surgical stress can induce profound decreases in triiodothyronine (T3) levels, the hemodynamic consequences of "stress-induced" hypothyroidism and T3 repletion are of increasing clinical interest. Available data generally support the likelihood of a beneficial effect associated with T3 replacement in brain-dead organ donors and in cases of low cardiac output following CPB. Although hypotheses have been advanced to account for these salutary effects, the mechanism by which T3 may augment hemodynamic performance has not been precisely defined, particularly in the acute setting. Although additional research is needed to clarify these and other issues, preliminary findings with T3 replacement indicate that such investigation is warranted.

Thyrotoxicosis and the heart

Many patients with thyrotoxicosis have clinical features that reflect the effects of excess thyroid hormone on the cardiovascular system. Thyrotoxicosis can aggravate preexisting cardiac disease and can also lead to atrial fibrillation, congestive heart failure, or worsening of angina pectoris. In elderly patients, these cardiac manifestations may dominate the clinical picture and warrant the measurement of the serum thyrotropin concentration. In the absence of preexisting cardiac disease, treatment of thyrotoxicosis usually results in a return of normal cardiac function.