Left ventricular function and hyperthyroidism

Hyperdynamic Right Heart Function in Graves' Hyperthyroidism Measured by Echocardiography Normalises on Restoration of Euthyroidism

BACKGROUND

Graves' hyperthyroidism commonly causes tachycardia and may result in pulmonary hypertension and high output cardiac failure. There is limited information regarding the effect of treatment on cardiac function measured using modern echocardiographic techniques.

METHODS

Eight individuals with Graves' hyperthyroidism, aged 22-64 years, underwent comprehensive transthoracic echocardiography at three time points: before treatment, two weeks after commencement of carbimazole, and at six months or more when euthyroid. Exercise capacity was assessed using the 6-minute-walk-distance (6MWT), and quality of life was assessed by Medical Outcome Study 36-item Short-Form Health Status Survey.

RESULTS

All individuals were rendered euthyroid by final assessment. At presentation, there was evidence of hyperdynamic right ventricular function as measured by peak systolic velocity of the free wall of the tricuspid annulus, tricuspid annular plane systolic excursion and right ventricular ejection fraction, which normalised after resolution of thyrotoxicosis. Baseline heart rate correlated significantly with severity of the thyrotoxicosis for either free T4 (r = 0.91, p=0.01) or free T3 (r=0.94, p=0.001). No individual had measurable pulmonary hypertension. Cardiac output was significantly lower in the euthyroid compared to the thyrotoxic state (p=0.03). A higher baseline TSH-receptor antibody titre corresponded to a greater improvement in exercise capacity (r=0.76, p<0.05) and physical quality of life (r=0.73, p<0.05) on resolution of the hyperthyroidism.

CONCLUSION

Graves' hyperthyroidism causes increased cardiac output and a hyperdynamic right ventricle which normalise on restoration of the euthyroid state.

Heart Failure in Thyrotoxic Cardiomopathy: Extracorporeal Membrane Oxygenation Treatment for Graves' Disease

Thyrotoxicosis-induced cardiomyopathy and consequent heart failure is one of the most grave complications of uncontrolled hyperthyroidism. In such patients, early recognition of thyrotoxicosis, and directed antithyroid therapy can lead to rapid normalization of left ventricular function. Herein, we present a case of a 29-year-old male with Graves' disease who developed heart failure with severe deterioration of left ventricular function and eventually, circulatory collapse. Height and weight of the patient were 1.8 m and 84 kg, respectively. The patient was placed on venoarterial extracorporeal membrane oxygenation for immediate circulatory support, with restoration of cardiac function after 6 days.

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.

Dipper and non-dipper blood pressure 24-hour patterns: circadian rhythm-dependent physiologic and pathophysiologic mechanisms

Neuroendocrine mechanisms are major determinants of the normal 24-h blood pressure (BP) pattern. At the central level, integration of the major driving factors of this temporal variability is mediated by circadian rhythms of monoaminergic systems in conjunction with those of the hypothalamic-pituitary-adrenal, hypothalamic-pituitary-thyroid, opioid, renin-angiotensin-aldosterone, plus endothelial systems and specific vasoactive peptides. Humoral secretions are typically episodic, coupled either to sleep and/or the circadian endogenous (suprachiasmatic nucleus) central pacemaker clock, but exhibiting also weekly, monthly, seasonal, and annual periodicities. Sleep induction and arousal are influenced also by many hormones and chemical substances that exhibit 24-h variation, e.g., arginine vasopressin, vasoactive intestinal peptide, melatonin, somatotropin, insulin, steroids, serotonin, corticotropin-releasing factor, adrenocorticotropic hormone, thyrotropin-releasing hormone, endogenous opioids, and prostaglandin E2, all with established effects on the cardiovascular system. As a consequence, physical, mental, and pathologic stimuli that activate or inhibit neuroendocrine effectors of biological rhythmicity may also interfere with, or modify, the temporal BP structure. Moreover, immediate adjustment to exogenous components/environment demands by BP rhythms is modulated by the circadian-time-dependent responsiveness of biological oscillators and their neuroendocrine effectors. This knowledge contributes to a better understanding of the pathophysiology of abnormalities of the 24-h BP pattern and level and their correction through circadian rhythm-based chronotherapeutic strategies.

Cardiac performance in hyperthyroidism assessed by systolic time intervals and radionuclide ventriculography

Systolic time intervals (STI) and radionuclide ventriculography (RNV) were used in the assessment of cardiac performance in 22 patients with hyperthyroidism before and after antithyroid treatment. STI as well as RNV showed enhanced myocardial contractility which was normalized after antithyroid treatment. Beta-blocker treatment did not influence the hypercontractility in hyperthyroidism. This implies that beta-blockers alone cannot be regarded as satisfactory long-term treatment and that mechanisms other than increased sympathoadrenal drive are involved in the hypercontractility in hyperthyroidism. RNV suggested valvular regurgitation, probably of the mitral valve, in 11 patients. Possible hemodynamic consequences are discussed.

Hyperthyroid heart disease

The heart is an organ sensitive to the action of thyroid hormone, and measurable changes in cardiac performance are detected with small variations in thyroid hormone serum concentrations. Most patients with hyperthyroidism experience cardiovascular manifestations, and the most serious complications of hyperthyroidism occur as a result of cardiac involvement. Recent studies provide important insights into the molecular pathways that mediate the action of thyroid hormone on the heart and allow a better understanding of the mechanisms that underlie the hemodynamic and clinical manifestations of hyperthyroidism. Several cardiovascular conditions and drugs can interfere with thyroid hormone levels and may pose a difficulty in interpretation of laboratory data in patients with suspected thyroid heart disease. The focus of this report is a review of the current knowledge of thyroid hormone action on the heart and the clinical and hemodynamic laboratory findings as well as therapeutic management of patients with hyperthyroid heart disease.

Cardiovascular and Renal Manifestations of Hyperthyroidism

In the simplest terms, hyperthyroidism is the clinical syndrome that results from an excess of thyroid hormones. This review considers the effects of hyperthyroidism on the cardiovascular and renal systems by reviewing the available literature on the clinical manifestations of this syndrome in the cat and also considering experimental studies and experience in other species, including human beings.

Operative contractility: A functional concept of the inotropic state

1. Initial unsuccessful attempts to evaluate ventricular function in terms of the 'heart as a pump' led to focusing on the 'heart as a muscle' and to the concept of myocardial contractility. However, no clinically ideal index exists to assess the contractile state. The aim of the present study was to develop a mathematical model to assess cardiac contractility. 2. A tri-axial system was conceived for preload (PL), afterload (AL) and contractility, where stroke volume (SV) was represented as the volume of the tetrahedron. Based on this model, 'operative' contractility ('OperCon') was calculated from the readily measured values of PL, AL and SV. The model was tested retrospectively under a variety of different experimental and clinical conditions, in 71 studies in humans and 29 studies in dogs. A prospective echocardiographic study was performed in 143 consecutive subjects to evaluate the ability of the model to assess contractility when SV and PL were measured volumetrically (mL) or dimensionally (cm). 3. With inotropic interventions, OperCon changes were comparable to those of ejection fraction (EF), velocity of shortening (Vcf) and dP/dt-max. Only with positive inotropic interventions did elastance (Ees) show significantly larger changes. With load manipulations, OperCon showed significantly smaller changes than EF and Ees and comparable changes to Vcf and dP/dt-max. Values of OperCon were similar when AL was represented by systolic blood pressure or wall stress and when volumetric or dimensional values were used. 4. Operative contractility is a reliable, simple and versatile method to assess cardiac contractility.

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.

Severe reversible dilated cardiomyopathy and hyperthyroidism: case report and review of the literature

OBJECTIVE

To describe a case of a 46-year-old woman with Graves' disease and reversible low-output congestive heart failure and present a comparative analysis of 23 similar cases reported in the literature.

METHODS

A detailed case report is presented. In addition, a review of the pertinent literature published between 1960 and 2002 was performed to identify similar cases of dilated cardiomyopathy and thyrotoxicosis and to assess the findings in these patients.

RESULTS

A 46-year-old woman without primary heart disease was admitted to the hospital with Graves' thyrotoxicosis and severe low-output congestive heart failure. Her left ventricular ejection fraction (LVEF) at the time of initial assessment was less than 20%, and her condition was categorized as New York Heart Association (NYHA) functional class III. Nineteen months after she was treated for hyperthyroidism, her LVEF was 49% and her status was NYHA class I. A severe hypotensive episode occurred when b-adrenergic blockade therapy was initiated. The group of 23 similar cases from the literature plus our currently described patient had a mean age of 45 years, a male-to-female ratio of 1:1.2, Graves' disease as the principal cause, and LVEF improvement from 29% to 58%.

CONCLUSION

Dilated cardiomyopathy is an unusual manifestation of hyperthyroidism with unclear cause. Clinicians should be aware of this entity because it is treatable and hypotension can occur if b-adrenergic blockade treatment is initiated.

Myocardial effects of cyclic AMP phosphodiesterase inhibition are dampened in thyroxine-induced cardiac hypertrophy

We tested the hypothesis that the increase in myocardial O2 consumption (MVO2) and myocardial wall thickening in response to milrinone would not be limited by thyroxine (T4)-induced (0.5 mg/kg for 16 days) cardiac hypertrophy. Anesthetized open-chest New Zealand white rabbits were divided into four groups: control vehicle (CV, n = 5), control milrinone (CM, n = 8), T4 vehicle (T4V, n = 7), and T4 milrinone (T4M, n = 9). Vehicle or milrinone (10(-3) M) were topically applied to the left ventricular epicardium for 15 min. Coronary blood flow (radioactive microspheres) and O2 extraction (microspectrophotometry) were used to determine O2 consumption. Cyclic AMP levels were determined by radioimmunoassay. T4 increased the heart weight to body weight ratio from 2.6 +/- 0.1 to 3.1 +/- 0.1 (g/kg). T4 rabbits had significantly higher baseline heart rates, blood pressures, and dP/dtmax and both subepicardial (EPI) and subendocardial (ENDO) blood flows. Topical application of milrinone did not have significant hemodynamic effects in either group. Baseline cyclic AMP levels (pmol/g) in the EPI and ENDO myocytes were comparable between control and T4 rabbits (CVEPI = 599 +/- 34, CVENDO = 532 +/- 26, T4VEPI = 656 +/- 42, T4VENDO = 657 +/- 17). Milrinone increased cyclic AMP in all groups although the increases were less in the T4 rabbits (CMEPI = 742 +/- 115, CMENDO = 698 +/- 101, T4MEPI = 742 +/- 103, T4MENDO = 690 +/- 55). Baseline MVO2 (ml O2/min/100 g) was significantly higher in T4 rabbits than controls (T4VEPI = 17.7 +/- 3.5 vs CVEPI = 8.5 +/- 1.5, T4VENDO = 17.2 +/- 3.2 vs CVENDO = 9.2 +/- 1.5). Significant increases in MVO2 were noted with the addition of milrinone in control (CMEPI = 14.8 +/- 3.0, CMENDO = 13.5 +/- 1.6) and T4 (T4MEPI = 25.5 +/- 3.4, T4MENDO = 22.0 +/- 3.3) rabbits; however, the percentage increase in MVO2 was significantly greater in controls (CEPI = 73%, CENDO = 47%) than T4 (T4,EPI = 44%, T4,ENDO = 28%). Thus, although the cyclic AMP phosphodiesterase activity was comparable between T4 rabbit hearts and controls, the metabolic effects and cyclic AMP effects of milrinone were dampened in this form of hypertrophy.

Thyroid hormone and cardiovascular disease

Thyroid hormone directly affects the heart and peripheral vascular system. The hormone can increase myocardial inotropy and heart rate and dilate peripheral arteries to increase cardiac output. An excessive deficiency of thyroid hormone can cause cardiovascular disease and aggravate many preexisting conditions. In severe systemic illness and after major surgical procedures changes in thyroid function can occur, leading to the "euthyroid sick syndrome." Patients will have normal or decreased levels of T4, decreased free and total T3, and usually normal levels of thyroid stimulating hormone. This syndrome may be an adaptive response to systemic illness that usually will revert to normal without hormone supplementation as the illness subsides. Recently, however, many investigators have explored the benefits of thyroid hormone supplementation in those diseases associated with euthyroid sick syndrome. Thyroid hormone's effects on the cardiovascular system make it an attractive therapy for those patients with impaired hemodynamics and low T3. Thyroid hormone has also been considered a treatment for patients with congestive heart failure, for patients undergoing cardiopulmonary bypass and heart transplantation, and for patients with hyperlipidemia. At present there is no evidence suggesting a favorable treatment outcome using thyroid hormone supplementation for any systemic condition except in those patients with documented hypothyroidism.

Myocardial damage does not occur in untreated hyperthyroidism unless associated with congestive heart failure

Even in the absence of underlying cardiac disease, hyperthyroidism has seldom been reported to be associated with left ventricular dysfunction and congestive heart failure. The left ventricular function invariably improves with achievement of euthyroid status. Anecdotal autopsy reports have suggested that myocardial necrosis associated with hyperthyroidism may be responsible for congestive heart failure. This study prospectively evaluates the role of myocardial necrosis in untreated hyperthyroidism by imaging with Indium-111 antimyosin antibody. Thirteen consecutive patients (7 men and 6 women, mean age 36 +/- 11 years) with hyperthyroidism and Graves' disease (10 patients), subacute thyroiditis (2 patients), or multinodular goiter (1 patient) formed the basis of the study. The T4 levels ranged from 33 to 183 pmol/L (mean 103 +/- 47 pmol/L) and cardiac output from 5.47 to 11.0 L/min (mean 7.17 +/- 1.75 L/min). Two patients had clinical congestive heart failure and mildly depressed left ventricular ejection fraction. Both patients had scintigraphic evidence of myocardial damage with abnormal antimyosin scans. In the remaining 11 patients with normal left ventricular ejection fraction, no antimyosin uptake was observed. The reevaluation of two patients with abnormal initial scans 6 to 8 months after treatment revealed euthyroid status, resolution of antimyosin uptake, and normalization of left ventricular function. This study indicates that myocardial necrosis may be detected in a small proportion of patients with hyperthyroidism, which could contribute to left ventricular systolic dysfunction.

Effects of thyroid hormone on cardiac beta-adrenergic responsiveness in conscious baboons

BACKGROUND

Many of the cardiovascular manifestations of thyroid hormone excess resemble those produced by sympathoadrenal stimulation. The objective of this study was to determine the effects of thyroid hormone excess on myocardial beta-adrenergic expression and responsiveness to infused agonists in the primate heart.

METHODS AND RESULTS

The responses of left ventricular isovolumic contraction (dP/dt(max)) and relaxation (tau) during graded dobutamine infusion were studied both before and after 4 weeks of thyroid hormone administration in 8 chronically instrumented baboons. At matched (atrially paced) heart rates, thyroid hormone significantly increased resting dP/dt(max) (3073+/-1034 versus 2318+/-829 mm Hg/s, P<.05) and decreased tau (24.0+/-5.5 versus 28.2+/-5.4 ms, P<.05). The change from baseline for dP/dt(max) and tau in response to beta1-adrenergic stimulation was significant at each dobutamine dose (2.5 to 10 microg x kg(-1) x min(-1)), but when expressed as a percent change, it was similar before versus after thyroid hormone. Similar changes were found when beta2-adrenergic stimulation was produced by terbutaline infusion in three additional baboons. beta-Adrenergic receptor (betaAR) expression was higher in five thyroxine-treated than in five control baboons (37.4+/-1.2 versus 15.7+/-3.2 fmol/mg, P<.001), and this was due to a greater increase in the beta2AR (5.9+/-1.5 to 20.6+/-1.2 fmol/mg, P<.001) than the beta1AR (9.7+/-1.7 to 16.8+/-0.1 fmol/mg, P<.01) subtype.

CONCLUSIONS

In the primate heart, thyroid hormone produces positive inotropic and lusitropic effects in the resting state and upregulates both beta1AR and beta2AR, with the beta2AR increase predominating. At equivalent rates, however, thyroid hormone excess does not appear to enhance the sensitivity of left ventricular contractility and relaxation to either beta1- or beta2-adrenergic stimulation.

Endocrine mechanisms of blood pressure rhythms

The temporal organization of blood pressure is mainly controlled by neuroendocrine mechanisms. The monoaminergic systems appear to integrate the major driving factors of temporal variability, but evidence also indicates a role of the hypothalamic-pituitary-adrenal, hypothalamic-pituitary-thyroid, opioid, renin-angiotensin-aldosterone, and endothelial systems as well as other vasoactive peptides. Although their hormonal secretions are typically episodic, the probability of secretory episodes is "gated" by mechanisms that are coupled either to sleep or to an endogenous pacemaker which usually is predominantly (though not only) circadian. Many hormones with established actions on the cardiovascular system (arginine vasopressin, vasoactive intestinal peptide, melatonin, somatotropin, insulin, steroids, serotonin, CRF, ACTH, TRH, endogenous opioids, and prostaglandin E2) are also involved in sleep induction or arousal. Hence, physical, mental, and pathologic stimuli, which may drive activation or inhibition of these neuroendocrine effectors of biologic rhythmicity, may also interfere with the temporal blood pressure structure. On the other hand, the immediate adaptation of the exogenous components of blood pressure rhythms to the demands of the environment are modulated by the circadian-time-dependent responsiveness of the biologic oscillators and their neuroendocrine effectors. These notions may contribute to a better understanding of the pathophysiology and therapeutics of changes in blood pressure.

Congestive heart failure due to reversible cardiomyopathy in patients with hyperthyroidism

The authors describe the clinical characteristics and response to therapy of seven patients with hyperthyroidism, dilated cardiomyopathy, and low-output cardiac failure. All patients (4 women and 3 men, age 47 +/- 4 years, mean +/- standard error of the mean) were admitted with the primary diagnosis of congestive heart failure. The cause of hyperthyroidism was Graves' disease in six patients, and toxic multinodular goiter in one. On admission, the mean serum T4 was 21 +/- 1 microgram/dL and mean serum T3:411 +/- 77 ng/mL, and serum thyroid-stimulating hormone was suppressed ( < 0.03 microU/mL) in all patients. Two-dimensional echocardiogram showed biventricular or four chamber dilatation and impaired left ventricular performance. Therapy of heart failure and hyperthyroidism resulted in rapid clinical improvement. During follow-up (5 months to 9 years), left ventricular ejection fraction improved from a mean of 28% to a mean ejection fraction of 55% (P < 0.01). Resolution of dilated cardiomyopathy with normalization of systolic function was achieved in five patients, and improvement from severe to mild left ventricular dysfunction was observed in two patients. We conclude that some patients with hyperthyroidism may have a reversible form of dilated cardiomyopathy and "low-output failure." Assessment of thyroid hormone status in patients with heart failure might permit the identification of patients with dilated cardiomyopathy and thyrotoxicosis who are likely to have reversible cardia dysfunction.

Doppler echocardiographic evaluation of left ventricular diastolic function in acute hypothyroidism

OBJECTIVE

Left ventricular diastolic dysfunction is an important cause of symptomatic heart failure. Previous studies suggest that thyroid dysfunction affects left ventricular diastolic function but the underlying mechanisms remain controversial. The study was undertaken to asses the influence of acute hypothyroidism on left ventricular diastolic function and to elucidate possible underlying mechanisms by means of Doppler echocardiography in a group of athyreotic patients, whose thyroid state depended only on external thyroid hormone supply and could therefore easily be controlled.

PATIENTS

Eleven patients (5 men, 6 women, aged 20-55 years), who had had total thyroidectomy, were investigated during mild hyperthyroidism and during acute hypothyroidism. Additionally, 11 healthy control subjects aged 25-51 years were included in the study.

DESIGN

M-mode echocardiography of the left ventricle and pulsed-wave Doppler echocardiography of the transmitral flow velocity pattern were carried out.

RESULTS

Acute hypothyroidism produced a decrease of left ventricular end-diastolic diameter from 48 +/- 5 to 46 +/- 5 mm (mean +/- SD P < 0.05), of peak velocity of early diastolic filling from 0.52 +/- 0.10 to 0.42 +/- 0.05 m/s (P < 0.05), of peak velocity of late diastolic filling from 0.42 +/- 0.10 to 0.36 +/- 0.09 m/s (P < 0.05), and a decreased time-velocity integral of early diastolic filling (6.2 +/- 1.8 vs 5.1 +/- 0.7 cm, P < 0.05). The other M-mode and Doppler echocardiographic parameters did not differ between the hyperthyroid and the hypothyroid states.

CONCLUSIONS

The observed changes of the trans-mitral flow velocity pattern during acute hypothyroidism can be attributed to a reduction of pre-load. There is no direct evidence that acute hypothyroidism affects the intrinsic diastolic properties of the left ventricle.

The effects of hyperthyroidism on muscular dystrophy in the mdx mouse: greater dystrophy in cardiac and soleus muscle

Muscle damage and repair were studied in mdx mice treated with triiodothyronine (T3) for 14 days. Hindlimb and cardiac muscles were examined for the severity of dystrophy, the degree of muscle centronucleation, and fiber size. In control and mdx mice, cardiac hypertrophy and skeletal muscle atrophy were present after T3 treatment. Both cardiac and soleus (but not fast-twitch) muscles had larger, more frequent dystrophic lesions in T3-treated mdx mice, and mdx soleus had an increased area of new myotubes after T3. Skeletal myogenesis in mdx mice may have been delayed by excess T3, possibly related to the general reduction in staining for basic fibroblast growth factor in hyperthyroid mice. These are the first observations of a metabolic perturbation which worsens mdx dystrophy and possibly repair in a muscle-specific manner, and are likely related to T3-induced changes in myosin heavy chain expression, and to increased mechanical strain on dystrophin-deficient muscles.

Cardiac function in thyroid disease: clinical features and management considerations

Thyroid disease is often manifested by cardiac abnormalities. The site of the cardiac actions of thyroid hormone, whether from a direct, nuclear effect or an extranuclear effect, remains to be established. Nuclear effects are delayed 1/2 to 1 hour after administration of thyroid hormone, require ongoing protein synthesis, and are thought to result from the binding of thyroid hormone to two separate isoforms of the nuclear thyroid hormone receptor. This binding, which is specific to thyroid hormone response elements, stimulates transcription and results in translation of specific enzymes or contractile proteins. Extranuclear effects may influence plasma membrane transport of calcium, sugar, and amino acids in addition to directly influencing mitochondria and are very rapid, occurring within minutes. It is possible that there exists an interaction between the adrenergic system and the thyroid hormone system, which may also contribute to the cardiac actions of thyroid hormone. This review highlights the clinical manifestations of thyroid disease and the mechanisms of thyroid hormone involved in the cardiac abnormalities.

Triiodothyronine, beta-adrenergic receptors, agonist responses, and exercise capacity

Although thyroid hormone excess results in increased beta-adrenergic receptor density or agonist responses in some cells of experimental animals, the role of these effects in contributing to clinical manifestations of hyperthyroidism in human subjects is unclear. To shed further light on this issue, we characterized the effect of 2 weeks of excess triiodothyronine administration on cardiac and metabolic responses to graded-dose isoproterenol infusion, skeletal muscle beta-adrenergic receptor density, and physiologic determinants of exercise capacity in young healthy subjects. The slope of the heart rate response to isoproterenol was 36% greater (p < 0.05) after triiodothyronine administration. In addition, beta-adrenergic receptor density was increased (p < 0.01) in all types of skeletal muscle fibers. Maximal oxygen uptake during treadmill exercise declined 5% (p < 0.001) after triiodothyronine administration because of a decrease in the arteriovenous oxygen difference (p < 0.05). The plasma lactate response to submaximal exercise was 25% greater (p < 0.01) in the hyperthyroid state. These effects were paralleled by a decrement in skeletal muscle oxidative capacity and a decrease in cross-sectional area of type 2A skeletal myocytes. Thus, thyroid hormone excess enhances cardiac beta-adrenergic sensitivity under in vivo conditions in human subjects. Nevertheless, exercise capacity is diminished in the hyperthyroid state, an effect that may be related to reduced skeletal muscle oxidative capacity and type 2A fiber atrophy.

Non-beta-adrenergic-mediated peripheral circulatory hyperkinesia in hyperthyroidism

Systolic time intervals and brachial circulation, evaluated by pulsed Doppler in terms of arterial diameter, blood velocity and flow, and vascular resistance, were studied in 12 hyperthyroid patients and in 12 normal controls. In patients, arterial circulation was studied before and during mechanical exclusion of the hand, and hemodynamic measurements were repeated after beta-blocker treatment and after obtainment of euthyroid state. Compared with controls, patients had higher heart rate (P < 0.001), lower systolic time intervals (P < 0.05, P < 0.01), and higher blood velocity (P < 0.05). Beta blockade decreased heart rate (P < 0.05, P < 0.001) but did not change systolic time intervals and arterial circulation. Euthyroid state decreased heart rate (P < 0.01), preejection period (P < 0.01), and blood velocity (P < 0.01) and flow (P < 0.05). The decreases in velocity and flow before hand exclusion when euthyroid state was obtained were correlated with hyperthyroid values of velocity and flow respectively (r = 0.85, r = 0.90, P < 0.01, P < 0.001). Vascular resistance during hand exclusion was correlated negatively with serum T3 level during hyperthyroid and euthyroid states. Thus, thyroid hormones but not beta-adrenoreceptors participate in the peripheral hyperkinesia of hyperthyroidism.

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.

Effect of hyperthyroidism of short duration on cardiac sensitivity to beta-adrenergic stimulation

The effect of hyperthyroidism on cardiac sensitivity to beta-adrenergic stimulation in humans is controversial. To determine whether heart rate and left ventricular contractile sensitivity to beta-adrenergic stimulation are altered by hyperthyroidism in human subjects, the frequency, velocity and extent of left ventricular shortening at rest and during a 4-stage graded dose isoproterenol infusion were characterized in eight young healthy subjects before and after 2 weeks of daily administration of 100 micrograms of triiodothyronine (T3). The rate and extent of left ventricular shortening were determined by Doppler and two-dimensionally guided M-mode echocardiography. In the hyperthyroid state, heart rate at rest was faster (57 +/- 3 vs. 68 +/- 4 beats/min; p less than 0.001) and the slope of the relation of heart rate to the rate of isoproterenol infusion was 36% steeper (1,538 +/- 126 vs. 1,131 +/- 95; p less than 0.05). The left ventricular ejection time was shorter and the mean velocity of left ventricular circumferential fiber shortening (mVcf) was greater during all stages of isoproterenol infusion in the hyperthyroid versus the euthyroid state (p less than 0.01). After adjustment for the faster heart rate after T3 administration, left ventricular ejection time and mVcf were similar in the euthyroid and hyperthyroid states at baseline and during maximal beta-adrenergic stimulation but shortened and enhanced, respectively, during stages 1 and 2 of isoproterenol infusion (p less than 0.05). There was no effect of T3 administration on left ventricular mass, dimensions, end-systolic wall stress or stroke volume at rest or during any stage of isoproterenol infusion. These results indicate that in human subjects hyperthyroidism of short duration increases the sensitivity of heart rate and left ventricular shortening velocity to beta-adrenergic stimulation in the absence of changes in left ventricular mass, loading conditions or extent of shortening.

Peripartum cardiac failure in a woman with Graves' disease

A case of peripartum cardiac failure is reported in a 20-year-old gravida 3, para 3 black female. The patient was 6 weeks postpartum. Graves' disease had been diagnosed in the first trimester of her pregnancy. The patient presented to the emergency department with complaints of fever, abdominal pain, shortness of breath, and chest pain. Physical examination revealed signs of congestive heart failure and anasarca. Chest x-ray revealed bilateral pleural effusions, and an abdominal series was consistent with ascites. Bedside electrocardiogram revealed pan-hypokinesis of all four cardiac chambers. The authors believe that this is the first case reported in the literature of peripartum cardiac failure occurring in a patient with Graves' disease.

Disturbance of osmoregulated thirst and vasopressin secretion in thyrotoxicosis

OBJECTIVE

To assess the effect of untreated thyrotoxicosis on osmoregulated thirst sensation and AVP secretion.

DESIGN

Measurements were made at 30-minute intervals while untreated thyrotoxic patients were given sodium chloride 855 mmol/l intravenously for 2 hours followed by water drinking ad libitum for 2 hours. The protocol was repeated when the patients were euthyroid.

PATIENTS

Eight newly diagnosed thyrotoxic patients were studied.

MEASUREMENTS

Thirst sensation (visual analogue scale), plasma osmolality, AVP and plasma renin activity were measured.

RESULTS

Prior to osmotic stimulation and after plasma osmolality had been returned to normal by drinking water, thirst sensation was increased in the thyrotoxic state. Plasma AVP showed an exaggerated response to hypertonic saline in the patients when they were thyrotoxic. Increasing plasma osmolality produced a linear increase in thirst sensation and log linear increase in plasma AVP. However, in the thyrotoxic state both these relations were altered. The apparent osmolar thresholds for onset of thirst sensation and AVP release were similar (281 and 280 mosm/kg respectively) and were reduced similarly in the thyrotoxic state (269 and 274 mosm/kg respectively).

CONCLUSIONS

The osmostat mechanisms which regulate thirst sensation and AVP release are reset in the thyrotoxic state. The responses of thirst sensation and of plasma AVP to increasing plasma osmolality are altered similarly, suggesting that thyrotoxicosis affects both homeostatic functions by a common mechanism.

Thyroid hormone and the cardiovascular system

To understand the pathophysiology of thyroid heart disease, it is necessary to recognize that thyroid hormone has effects on both the peripheral circulation and the myocardium. One of the earliest responses to thyroid hormone administration is a decline in systemic vascular resistance and an increase in cardiac output and cardiac contractility. In many ways, this response is similar to the cardiovascular response to exercise and is associated with increased left ventricular work. The majority of cardiac adaptations to changes in thyroid function are physiologic; however, certain patients do demonstrate clinical evidence of cardiac disease. Atrial arrhythmias, limitations in exercise tolerance, and congestive heart failure are reported to occur as a result of hyperthyroidism and are more common in older patients. Thyroid hormone also plays an important role in the regulation of blood pressure. Diastolic hypertension is a common accompaniment of hypothyroidism. By understanding the mechanisms by which thyroid hormone affects both the peripheral circulation as well as the myocardium, it is possible to predict the clinical response to the treatment of various thyroid disease states.

Effect of beta adrenoceptors and thyroid hormones on velocity and acceleration of peripheral arterial flow in hyperthyroidism

Brachial artery flow patterns were studied in 10 hyperthyroid and 10 normal subjects. Mean blood velocity and flow were evaluated by pulsed Doppler, and peak systolic acceleration was calculated by computer-assisted digitization of the instantaneous velocity curve. Compared to control subjects, hyperthyroid patients had higher velocity and flow (p less than 0.01, p less than 0.02) and higher peak systolic acceleration (p less than 0.01). In hyperthyroid patients, measurements were repeated after (1) mechanical exclusion of the hand from brachial circulation, (2) short-term beta-blocker treatment and (3) inducement of the euthyroid state. Exclusion of the hand reduced velocity and flow (p less than 0.001) but did not change peak systolic acceleration. Beta blockade induced disparate changes of velocity and flow but reduced peak systolic acceleration (p less than 0.05). In the euthyroid state, decreased blood velocity (p less than 0.01), flow (p less than 0.02) and acceleration (p less than 0.02) were observed. A hyperkinetic arterial circulation consisting of an increase in both velocity and acceleration is thus observable in hyperthyroidism. Hand exclusion showed that velocity seems to be influenced by peripheral factors while beta blockade suggests that acceleration is dependent of beta 1 adrenoceptors. Comparison between euthyroidism and hyperthyroidism indicates that both mean blood velocity and peak systolic acceleration are influenced by thyroid hormones.

Left ventricular function at rest and during exercise in acute hypothyroidism

The effect of hypothyroidism on left ventricular function at rest and during exercise was studied in nine patients without demonstrable cardiovascular disease who had had total thyroidectomy and ablative radioiodine treatment for thyroid cancer. Radionuclide ventriculography and simultaneous right heart catheterisation were performed while the patients were hypothyroid two weeks after stopping triiodothyronine treatment (to permit routine screening for metastases) and while they were euthyroid on thyroxine replacement treatment. When the patients were hypothyroid, cardiac output, stroke volume, and end diastolic volume at rest were all lower and peripheral resistance was higher than when they were euthyroid. Pulmonary capillary wedge pressure, right atrial pressure, heart rate, left ventricular ejection fraction, and the systolic pressure:volume relation of the left ventricle, which was used as an estimate of the contractile state, were not significantly different when the patients were hypothyroid or euthyroid. During exercise, heart rate, cardiac output, end diastolic volume, and stroke volume were higher when the patients were euthyroid than when they were hypothyroid. Again, pulmonary capillary wedge pressure, ejection fraction, and the systolic pressure:volume relation were similar in both thyroid states. The data suggest that the alterations in cardiac performance seen in short term hypothyroidism are primarily related to changes in loading conditions and exercise heart rate; they do not suggest that acute thyroid hormone deficiency has a major effect on the contractile properties of the myocardium.

Plasma levels of atrial natriuretic peptide in hyperthyroidism

We measured plasma atrial natriuretic peptide (ANP) levels in 17 patients with newly diagnosed thyrotoxicosis. ANP was elevated compared to a group of healthy controls and fell to normal after treatment. Plasma cyclic guanosine monophosphate was also raised in untreated patients. Elevated circulating levels of ANP may play a part in the haemodynamic changes of hyperthyroidism.

Effect of graded doses of tri-iodothyronine on ventricular myosin ATPase activity and isomyosin profile in young and old rats

Ventricular myosin ATPase activity, V1 isomyosin content and serum T3 (tri-iodothyronine) values decrease with age in male Fischer 344 rats. To determine if the age decrement in ATPase activity and V1 isomyosin content are caused by decreased T3 levels or an age-related decrease in V1 isomyosin induction by T3, 3-, 12- and 24-month-old male Fischer 344 rats were given constant T3 infusions by osmotic minipump. Rats at all ages were given 0.75, 5 and 15 micrograms(/100 g per 24 h) doses of T3, whereas 12- and 24-month-old rats were given an additional 0.4 microgram dose. In control rats, T3 levels decreased from 97 +/- 2.7 at 3 months to 75 +/- 4.7 ng/100 ml at 24 months. Likewise, Ca2+-activated myosin ATPase activity decreased from 1.04 +/- 0.05 to 0.68 +/- 0.05 mumol of Pi/min per mg of protein, and the relative proportion of V1 of isomyosin decreased from 90 +/- 4.0 to 26 +/- 2.0%. The lowest (0.4 microgram) T3 dose, which was sufficient to restore T3 levels in 24-month-old animals to 3-month control values, abolished the age decrement in myosin ATPase activity and markedly increased the proportion of V1 isomyosin present in the ventricle. These findings indicate that the senescent ventricle responds readily to small doses of T3 and strongly suggest that the age decrement in serum T3 levels is sufficient to contribute to the age-related decrease in myosin ATPase activity and V1 isomyosin content. Since these parameters correlate with ventricular contractility, the age decrement in T3 levels may also contribute to the decreased ventricular contractility and cardiac output observed in senescent rats.

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

Hyperthyroidism has been reported to affect all of the major determinants of left ventricular performance in a manner that would augment ventricular shortening characteristics. The hypothesis tested in this study is that reduced afterload in conjunction with increased preload and heart rate, rather than augmented contractility, accounts for much of the increase in left ventricular performance noted previously in these patients. To investigate this hypothesis, 11 hyperthyroid patients were evaluated serially over 4 +/- 2 months. With therapy, serum total thyroxin (T4) decreased significantly (p less than 0.001). Ventricular hemodynamics were assessed by two-dimensional targeted M-mode echocardiograms and calibrated carotid pulse tracings. Ventricular preload was estimated by end-diastolic dimension, whereas afterload was measured as end-systolic wall stress. Overall left ventricular performance was quantitated by the extent and velocity of shortening, whereas myocardial work was assessed by ventricular systolic stress-length relations. With therapy, overall left ventricular performance declined (p less than 0.01). This change was associated with no change in end-diastolic dimension or end-systolic wall stress, and a 24% fall in heart rate (p less than 0.01). This latter finding has been shown previously to have no significant effect on left ventricular contractile state over the range of heart rates encountered in this study. In all cases, the end-systolic stress/rate-corrected shortening velocity relation fell with attainment of normal thyroid status, characteristic of a decline in contractility. There was a strong positive correlation between left ventricular contractility and serum thyroid hormone level (r = 0.83). In addition, ventricular minute work declined with therapy (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperthyroid heart disease

The importance of cardiovascular system involvement in hyperthyroidism has been recognized for many years. In the middle-aged and elderly patient, often with mild but prolonged elevation of plasma thyroid hormones, symptoms and signs of heart failure and complicating atrial fibrillation may dominate the clinical picture and mask the more classical endocrine manifestations of the disease. Pitfalls in diagnosis and the importance of early recognition and treatment are discussed. Despite experimental evidence for a short-term inotropic action of thyroid hormone excess, clinical data support the existence of a reversible cardiomyopathy in hyperthyroidism with impaired contractile reserve. Enhanced myocardial performance at rest primarily reflects the peripheral actions of thyroid hormone excess. Most, if not all, of the cardiac abnormalities return to normal once a euthyroid state has been achieved, although atrial fibrillation may persist in a minority. Optimum treatment requires rapid and definitive antithyroid therapy, usually using a large dose of radio-iodine, and rapid control of heart failure. Systemic anticoagulation is indicated in the presence of atrial fibrillation and should be continued until sinus rhythm has been present for at least three months, either spontaneously or after cardioversion.

Delayed recovery of left ventricular function after antithyroid treatment. Further evidence for reversible abnormalities of contractility in hyperthyroidism

Sequential measurements of systolic time intervals, left ventricular dimensions, and the derived indices of contractility were undertaken at rest and during isometric exercise in 15 hyperthyroid patients before, during, and after antithyroid treatment. At rest hyperthyroidism was characterised by a shortened pre-ejection period and increased velocity of circumferential shortening of the left ventricle. During isometric exercise, however, the pre-ejection period increased significantly beyond that predicted for normal subjects, and the velocity of circumferential fibre shortening fell by 30%. In contrast, both the pre-ejection period and the velocity of circumferential fibre shortening were unchanged during exercise after a stable euthyroid state had been achieved for at least three months. Comparison between exercise responses and thyroid status during antithyroid treatment showed that a biochemical euthyroid state may be achieved many weeks before normalisation of contractile response to exercise. These findings support the hypothesis of reversible depression of left ventricular function in hyperthyroidism. Responses at rest principally reflect the peripheral actions of thyroid hormone excess.

Control of cardiac output in thyrotoxic calves. Evaluation of changes in the systemic circulation

The contribution of peripheral vascular factors to the high output state in thyrotoxicosis was examined in 11 calves treated with daily intramuscular injections of L-thyroxine (200 micrograms/kg) for 12-14 d. Thyroxine treatment increased cardiac output from 14.1 +/- 1.4 to 24.7 +/- 1.4 liters/min (P less than 0.001) and decreased systemic vascular resistance from 562 +/- 65 to 386 +/- 30 dyn-s/cm5 (P less than 0.01). Blood volume was increased from 65 +/- 4 ml/kg in the euthyroid state to 81 +/- 6 ml/kg when the animals were thyrotoxic (P less than 0.05). The role of low peripheral vascular resistance in maintenance of the high output state was evaluated by infusion of phenylephrine at two dosages (2.5 and 4.0 micrograms/kg per min). In the euthyroid state, no significant decrease in cardiac output was observed at either level of pressor infusion. In the thyrotoxic state, the higher dosage of phenylephrine increased peripheral resistance to the euthyroid control level and caused a small (6%) decrease in cardiac output (P less than 0.05). This small decrease in cardiac output probably could be attributed to the marked increase in left ventricular afterload caused by the pressor infusion as assessed from measurements of intraventricular pressure and dimensions. Changes in the venous circulation were evaluated by measurement of mean circulatory filling pressure and the pressure gradient for venous return in six animals during cardiac arrest induced by injection of acetylcholine into the pulmonary artery. Mean circulatory filling pressure increased from 10 +/- 1 mmHg in the euthyroid state to 16 +/- 2 mmHg (P less than 0.01) during thyrotoxicosis, while pressure gradient for venous return increased from 10 +/- 1 to 14 +/- 2 mmHg (P less than 0.02). These changes in venous return curves were not affected significantly by ganglionic blockade with trimethapan (2.0 mg/kg per min) before cardiac arrest. Thus, the high output state associated with thyrotoxicosis is not dependent upon a low systemic vascular resistance, but is associated with increases in blood volume, mean circulatory filling pressure, and pressure gradient for venous return.

Hemodynamic profile of constrictive pericarditis produced by a massive right pleural effusion

We report a 29-year-old female who presented with thyrotoxicosis and a massive right pleural effusion. Cardiac catheterization in the presence of the effusion revealed equalization of abnormally elevated right and left heart filling pressures. Repeat study after thoracentesis demonstrated normal intracardiac pressures, which were unchanged by volume loading with normal saline. This case report suggests that both extrinsic cardiac chamber compression produced by the large unilateral effusion and ventricular interdependence altered diastolic function of the right and left ventricle in a manner resembling constrictive pericarditis or restrictive cardiomyopathy.

Effect of timolol on clinical features and echocardiographic assessment of left ventricular function in hyperthyroidism

The effect of timolol, a beta-adrenoceptor blocking drug on the clinical status, thyroid status and left ventricular function as measured by serial M-mode echocardiographic recordings was assessed in a double-blind randomised study in 18 hyperthyroid patients. A significant clinical improvement was documented after 2 weeks of timolol treatment compared with placebo. There was no evidence that timolol impaired peripheral monodeiodination of thyroxine (T4). There were significant increases in left ventricular fractional shortening (Fr. Sh.) and velocity of circumferential shortening (Vcf) as well as a significant decrease in the left ventricular systolic internal dimension (LVIDs) (all P less than 0.01) in the untreated thyrotoxic patients compared with a normal euthyroid control group. After timolol treatment (2/52) there were significant increases in LVIDs and LVIDd and a significant decrease in Vcf (all P less than 0.05). No further changes occurred after a further 2/52 treatment with carbimazole. The cardiac data suggest that both an augmented sympathetic drive and a direct effect of thyroid hormone on myocardial contractility are mediators of the haemodynamic changes in hyperthyroidism.

Abnormal left ventricular function in hyperthyroidism: evidence for a possible reversible cardiomyopathy

We assessed the effects of exercise and beta-adrenoceptor blockade on left ventricular ejection fraction (LVEF) measured by radionuclide ventriculography in nine patients with uncomplicated hyperthyroidism. Patients were studied in both the hyperthyroid and euthyroid states. The hyperthyroid state was characterized by a high LVEF at rest but--paradoxically--by a significant fall (P less than 0.01) in LVEF during exercise. At the same workload and at the same heart rate, patients had a restoration of the normal rise in LVEF during exercise when they were euthyroid. The LVEF was greater during exercise (P less than 0.02) when the patients were euthyroid than when they were hyperthyroid. Pretreatment with propranolol caused similar reductions in resting LVEF in the hyperthyroid and euthyroid states; the drug attenuated the rise in LVEF during exercise when the patients were euthyroid, but did not influence the exercise-induced reduction in LVEF in hyperthyroidism. The abnormal left ventricular function observed during exercise in hyperthyroidism suggests a reversible functional cardiomyopathy, independent of beta-adrenoceptor activation, that is presumably a direct effect of an excess in circulating thyroid hormones.