Thyrotoxicosis and the heart

Disfunções mínimas da tiróide: hipotiroidismo subclínico e hipertiroidismo subclínico

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

Stroke is related to lower serum thyrotropin levels in patients with diabetes mellitus

INTRODUCTION

Low serum thyrotropin has been related to the presence of stroke as well as to a higher incidence of cardiovascular disease in the general population. Furthermore, abnormalities in serum thyrotropin have been observed in diabetic patients even if unaffected by known thyroid illness. On this basis we investigated whether stroke is associated with altered thyrotropin concentrations in a hospitalised population categorised for the presence of diabetes.

PATIENTS AND METHODS

This study used a database concerning all patients consecutively admitted to hospital and discharged alive with a diagnosis of stroke or of transient ischemic attacks (TIA) confirmed by clinical and CT criteria during an 18-month period. The study group was composed of 698 (392 M/306 F) patients, aged 74+/-12(SD) years of whom 372 were affected with TIA and 326 with stroke.

RESULTS

The median thyrotropin level was significantly lower in diabetic patients (0.91 mU/l) than in the non-diabetic group (1.3 mU/l; P=0.0001). Patients with stroke, compared to those with TIA, were older, had higher blood pressure, higher prevalence of diabetes and lower serum thyrotropin (median value in TIA group: 1.30 mU/l (95% CI 0.25-4.63) vs. 1.04 (95% CI 0.18-3.76) in the stroke group, P=0.03), stroke being significantly associated with reduced median thyrotropin only in diabetic patients (n=239; 0.82 mU/l, vs. 1.09 mU/l in diabetic group; P<0.05, and 1.21 mU/l vs. 1.37 mU/l in the non-diabetic group; P=NS). Stroke severity, as assessed by NIHSS, was weakly inversely related to thyrotropin levels. Finally, after adjusting for main confounders, the odds ratio for stroke in the first thyrotropin quartile was significantly higher only in diabetic patients (OR: 3.56; 95% CI: 1.55-8.19; P<0.01 by trend test).

CONCLUSIONS

In conclusion, our findings suggest that stroke is significantly associated with low serum thyrotropin in patients with diabetes.

Temporal and topographic ultrastructural alterations of rat heart myofibrils caused by thyroid hormone

In order to further our understanding regarding the temporal and topographic ultrastructural aspects of the myocardium under thyrotoxicosis, thyroxine (T4; 25 and 100 microg/100 g bw) was administered to young rats 24 hours after birth until 15 days. The animals were then sacrificed, the hearts excised and weighed, and the ventricle tissue samples were then processed for confocal and transmission electron microscopy. At 48/72 hours and 1 week after initiation of T4 treatment with 100 microg/100 g bw, numerous lamellar bodies (probably formed by phospholipids) progressively accumulated in the heart. These bodies were observed in the cytosol, inside mitochondria and in the extracellular matrix. At 2 weeks of T4 treatment with 100 microg/100 g bw, lamellar bodies were virtually absent. Changes in cell shape, disorganization of intercellular junctions, and substantial myofibrillar disarray were observed in many cardiomyocytes. A gradient of myofibrillar disarray, which increased in abundance and intensity from the endocardium to the epicardium, was also observed. Immunocytochemical staining for desmin showed that the arrangement of this protein was disorganized in many cells of T4-treated rats as compared with normal ones, confirming ultrastructural data. The predominant appearance of myofibrillar disarray, associated with disorganization of cytoskeletal proteins in the deep myocardium, may be due to higher mechanical wall stress and consequent higher metabolic demand. Alternatively, differential sensitivity of cardiomyocytes to thyroid hormone in different areas is also a possibility.

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.

Hyperthyroidism: a "curable" cause of congestive heart failure--three case reports and a review of the literature

With the increasing incidence of coronary artery disease and the aging population, the prevalence of congestive heart failure (CHF) is increasing. In the majority of these cases the etiology is underlying coronary artery disease. Other less common causes of CHF include valvular heart disease, hypertension, alcoholic cardiomyopathy, and dilated cardiomyopathy. In addition, there are rare causes, one of which is hyperthyroidism. Hyperthyroidism can affect the cardiovascular system in a variety of ways. The cardiovascular manifestations range from sinus tachycardia to atrial fibrillation and from a high cardiac output state to CHF due to systolic left ventricular dysfunction. If the underlying hyperthyroidism is recognized and treated early the CHF in such cases can be cured. The authors present three cases of CHF due to systolic left ventricular dysfunction secondary to hyperthyroidism, which showed considerable improvement in the left ventricular function once the hyperthyroidism was treated.

Functional and metabolic adaptation of the heart to prolonged thyroid hormone treatment

In heart failure, thyroid hormone (TH) treatment improves cardiac performance. The long-term effects of TH on cardiac function and metabolism, however, are incompletely known. To investigate the effects of up to 28 days of TH treatment, male Wistar rats received 3,3',5-triiodo-l-thyronine (200 microg/kg sc per day) leading to a 2.5-fold rise in plasma fatty acid (FA) level and progressive cardiac hypertrophy (+47% after 28 days) (P < 0.001). Ejection fraction (echocardiography) was increased (+12%; P < 0.05) between 7 and 14 days and declined thereafter. Neither cardiac FA oxidation, glycolytic capacity (homogenates) per unit muscle mass, nor mRNA levels of proteins involved in FA and glucose uptake and metabolism (Northern blots and microarray) were altered. After 28 days of treatment, mRNA levels of uncoupling proteins (UCP) 2 and 3 and atrial natriuretic factor were increased (P < 0.05). This indicates that TH-induced hypertrophy is associated with an initial increase in cardiac performance, followed by a decline in cardiac function and increased expression of UCPs and atrial natriuretic factor, suggesting that detrimental effects eventually prevail.

Perioperative evaluation and management of the patient with endocrine dysfunction

Whenever possible, endocrine disorders should be identified and evaluated prior to surgery. A plan for perioperative management of diabetes should be based on the type of diabetes, what diabetes medications are taken, the status of diabetes control, and what type of surgery is planned. Perioperative management of diabetes must include bedside glucose monitoring. Patients with mild hypothyroidism can safely proceed with elective surgery. Elective surgery should be postponed for patients with moderate or severe hypothyroidism. Patients who have mild hyperthyroidism can undergo elective surgery with preoperative beta blockade. Elective surgery should not be done on patients with moderate or severe hyperthyroidism until they are euthyroid. Patients with pheochromocytoma need to be identified and properly treated before surgery to prevent perioperative cardiovascular complications. Patients who take endogenous steroids should have the status of their HPA axis determined prior to surgery. If the patient is undergoing moderate or major surgical stress and has documented or presumed HPA suppression, then stress doses of steroids should be give perioperatively.

Thyroid hormone regulation of cardiac bioenergetics: role of intracellular creatine

The effect of thyroid hormone (T(3)) on the content of myocardial creatine (Cr), Cr phosphate (CrP), and high-energy adenine nucleotides and on cardiac function was examined. In the hearts of control and T(3)-treated rats perfused in vitro, while "low" and "high" contractile work was performed, T(3) treatment resulted in a approximately 50% reduction in CrP, Cr, total Cr content (Cr + CrP), and in the CrP-to-Cr ratio. In addition, there was a slight fall in myocardial content of ATP and a large rise in calculated free ADP (fADP), resulting in a significant decrease in the ATP-to-fADP ratio in the hearts of hyperthyroid compared with euthyroid rats. Moreover, there was a substantial decrease in the level of ATP in hearts of T(3)-treated rats under high work conditions. Importantly, the ratio of cardiac work to oxygen consumption was not altered by thyroid status. Treatment with T(3) also resulted in an almost threefold reduction in the content of Na(+)/Cr transporter mRNA in the ventricular myocardium and skeletal muscle but not in the brain. We conclude with the following: 1) changes in the expression of the Na(+)/Cr transporter mRNA correlate with Cr + CrP in the myocardium; 2) hearts of hyperthyroid rats contain lower levels of ATP and higher levels of fADP under both low and high work conditions but no reduction in efficiency of work output; and 3) the reduction in Cr and ATP in hearts of hyperthyroid rats may be the basis for the reduced maximal work capacity of the hyperthyroid heart.

Design of thyroid hormone receptor antagonists from first principles

It is desirable to obtain TR antagonists for treatment of hyperthyroidism and other conditions. We have designed TR antagonists from first principles based on TR crystal structures. Since agonist ligands are buried in the fold of the TR ligand binding domain (LBD), we reasoned that ligands that resemble agonists with large extensions should bind the LBD, but would prevent its folding into an active conformation. In particular, we predicted that extensions at the 5' aryl position of ligand should reposition helix (H) 12, which forms part of the co-activator binding surface, and thereby inhibit TR activity. We have found that some synthetic ligands with 5' aryl ring extensions behave as antagonists (DIBRT, NH-3), or partial antagonists (GC-14, NH-4). Moreover, one compound (NH-3) represents the first potent TR antagonist with nanomolar affinity that also inhibits TR action in an animal model. However, the properties of the ligands also reveal unexpected aspects of TR behavior. While nuclear receptor antagonists generally promote binding of co-repressors, NH-3 blocks co-activator binding and also prevents co-repressor binding. More surprisingly, many compounds with extensions behave as full or partial agonists. We present hypotheses to explain both behaviors in terms of dynamic equilibrium of H12 position.

Management of patients with thyroid disease: oral health considerations

BACKGROUND

The thyroid gland and its hormones play an important role in the regulation of growth, development and metabolic functions of the body. Thyroid diseases include a group of conditions that can affect the delivery of dental care.

LITERATURE REVIEWED

The authors conducted a MEDLINE search of the medical and dental literature concerning thyroid disease and its management published between 1980 and 2000. The authors found eight published articles concerning this topic in the dental literature; a few of the articles specifically addressed thyroid disease and dental care. They reviewed the medical literature within the scope of provision of dental care.

CONCLUSIONS

The oral health care professional can play a role in the screening of dental patients who have undiagnosed thyroid disease. In addition, to treat patients who have thyroid disease, a thorough understanding of the many related pathological conditions, as well as the signs and symptoms that can occur, is needed. Specific dental treatment protocols for these patients are not found in the medicodental literature published between 1980 and 2000.

CLINICAL IMPLICATIONS

As part of a health care team, the dentist plays an important role in detecting thyroid abnormalities. Modifications of dental care must be considered when treating patients who have thyroid disease.

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.

Endocrine Heart Disease

With the increasing prevalence of obesity and diabetes mellitus in the United States, associated cardiovascular disease is reaching epidemic proportions with staggering economic and societal impact. Numerous studies have demonstrated the poorer prognosis associated with chronic coronary artery disease and acute coronary syndromes in patients with diabetes compared with nondiabetic patients. Although the therapeutic strategy is largely the same for the two populations, proper management of the diabetic patient with cardiovascular disease must account for the associated metabolic disturbances. Thyroid disease is the next most common endocrine disorder that affects proper function of cardiovascular patients; all patients presenting with coronary artery disease or cardiac arrhythmias should undergo screening with a sensitive thyroid-stimulating hormone assay and appropriate treatment when necessary. Though these areas are the most common points of intersection between the cardiologist and endocrinologist, a thorough understanding of the impacts of each endocrine system on cardiac function is essential to recognize disease entities that often present with a cardiovascular manifestation or affect patients with a primary cardiovascular disease.

Effects of thyroid hormone on the arrhythmogenic activity of pulmonary vein cardiomyocytes

OBJECTIVES

This study was conducted to investigate the effects of thyroid hormone on the electrophysiological characteristics of pulmonary vein (PV) cardiomyocytes.

BACKGROUND

Hyperthyroidism is an important etiology of paroxysmal atrial fibrillation (AF). Pulmonary veins are known to initiate paroxysmal AF.

METHODS

The action potential and ionic currents were investigated in single rabbit PV and atrial cardiomyocytes with (hyperthyroid) and without (control) incubation of L-triiodothyronine using the whole-cell clamp technique.

RESULTS

Compared with the control cardiomyocytes, hyperthyroid PV and atrial cardiomyocytes had shorter action potential duration. Hyperthyroid PV cardiomyocytes had faster beating rates (1.82 +/- 0.13 Hz vs. 1.03 +/- 0.15 Hz, p < 0.005) and a higher incidence of delayed after depolarization (beating: 92% vs. 6%, p < 0.0001; non-beating: 45% vs. 3%, p < 0.005). However, only hyperthyroid PV beating cardiomyocytes had a higher incidence of early after depolarization (46% vs. 0%, p < 0.0001). The ionic current experiments showed that hyperthyroid PV beating cardiomyocytes had larger densities of overall slow inward (2.72 +/- 0.21 pA/pF vs. 2.07 +/- 0.19 pA/pF, p < 0.05), overall transient outward (1.39 +/- 0.21 pA/pF vs. 0.48 +/- 0.08 pA/pF, p < 0.001) and steady state outward currents (0.78 +/- 0.06 pA/pF vs. 0.58 +/- 0.04 pA/pF, p < 0.05) on depolarization and larger transient inward (0.021 +/- 0.004 pA/pF vs. 0.005 +/- 0.001 pA/pF, p < 0.001) on repolarization. By contrast, the hyperthyroid PV non-beating cardiomyocytes had larger densities of overall transient outward (1.01 +/- 0.14 pA/pF vs. 0.37 +/- 0.07 pA/pF, p < 0.001), steady state outward (0.61 +/- 0.06 pA/pF vs. 0.44 +/- 0.04 pA/pF, p < 0.05) and transient inward currents (0.011 +/- 0.002 pA/pF vs. 0.003 +/- 0.001 pA/pF, p < 0.05).

CONCLUSIONS

Thyroid hormone changes the electrophysiological activity of the PV cardiomyocytes. Increased automaticity and enhanced triggered activity may increase the arrhythmogenic activity of PVs in hyperthyroidism.

Electrophysiological abnormalities of the atrial muscle in patients with paroxysmal atrial fibrillation associated with hyperthyroidism

OBJECTIVE

Atrial fibrillation (AF) is common in patients with hyperthyroidism. Although the choice of an antiarrhythmic agent should be based on its electrophysiological effects and the electrophysiological properties of the arrhythmia in question, the atrial electrophysiological features of AF associated with hyperthyroidism are unknown. The purposes of this study are to clarify the atrial electrophysiological abnormalities of AF with hyperthyroidism, and to propose effective therapies for AF in patients with hyperthyroidism.

SUBJECTS AND DESIGN

This study included 117 patients who underwent electrophysiological study and were evaluated for thyroid function: 29 patients without AF or hyperthyroidism (Group I), 78 patients with lone paroxysmal AF (Group II), and 10 patients with paroxysmal AF and hyperthyroidism (Group III). The following electrophysiological parameters were assessed and measured quantitatively: (1) the incidence of abnormal right atrial electrograms during sinus rhythm, indicating areas of altered anatomy and conduction where AF is likely to develop; (2) the atrial effective refractory period (ERP); and (3) the atrial conduction delay (CD), which is induced by early atrial premature beats close to the atrial ERP and is thought to facilitate the occurrence of AF.

RESULTS

The incidence of abnormal right atrial electrograms during sinus rhythm was significantly higher in Group II (67.1%) than in Group I (20.0%, P < 0.001) and Group III (22.2%, P = 0.009). The atrial ERP was significantly shorter in Group III (187 +/- 7 ms) than in Group I (215 +/- 36 ms, P = 0.019) and Group II (208 +/- 28 ms, P = 0.022). The atrial CD was observed in Group III as well as in Group II.

CONCLUSIONS

Our data indicate that the electrophysiological features of paroxysmal AF associated with hyperthyroidism are essentially different from those of lone paroxysmal AF. In patients with paroxysmal AF and hyperthyroidism, a shortening of the refractory period in association with a facilitation of the atrial CD could be expected to increase the propensity for AF, and a pre-existent arrhythmogenic substrate might not be essential to the genesis of AF. These findings suggest that the agents that prolong the atrial ERP are effective against AF in patients with hyperthyroidism.

Subclinical hyperthyroidism as a risk factor for atrial fibrillation

OBJECTIVES

Atrial fibrillation is a well-known manifestation of hyperthyroidism. We studied whether subclinical hyperthyroidism with low serum thyrotropin concentrations and free thyroid hormone concentrations within the normal range in clinically euthyroid persons is a risk factor for subsequent atrial fibrillation.

METHODS

We studied 23,638 persons. The subjects were classified according to their serum thyrotropin concentrations: group 1 comprised those with normal values of serum thyrotropin concentration (>0.4-5.0 mU/L) and free tri-iodothyronine and free thyroxine concentrations were within the normal range (22,300 subjects), group 2 comprised those with both low serum thyrotropin values (</=0.03 mU/L) and elevated free tri-iodothyronine and free thyroxine concentrations (725 subjects), and group 3 comprised those with low values of serum thyrotropin (<0.4 mU/L) and free triiodothyronine and free thyroxine concentrations were within the normal range (613 subjects).

RESULTS

Atrial fibrillation was present in 513 persons (2.3%) in group 1 with normal values for serum thyrotropin, 100 (13.8%) in group 2 with overt hyperthyroidism, and 78 (12.7%) in group 3 with subclinical hyperthyroidism. The prevalence of atrial fibrillation in patients with low serum thyrotropin concentrations (<0.4 mU/L) was 13.3% compared with 2.3% in patients with normal values for serum thyrotropin (P <.01). The relative risk of atrial fibrillation in subjects with low serum thyrotropin and normal free tri-iodothyronine and free thyroxine concentrations, compared with those with normal concentrations of serum thyrotropin, was 5.2 (95% CI 2.1-8.7, P <.01).

CONCLUSION

A low serum thyrotropin concentration is associated with a >5-fold higher likelihood for the presence of atrial fibrillation with no significant difference between subclinical and overt hyperthyroidism.

Prediction of all-cause and cardiovascular mortality in elderly people from one low serum thyrotropin result: a 10-year cohort study

BACKGROUND

Low serum thyrotropin, in combination with normal concentrations of circulating thyroid hormones, is common, especially in elderly people and in individuals with a history of thyroid disease. We aimed to assess the long-term effects of subclinical hyperthyroidism on mortality.

METHODS

We did a population-based study of mortality in a cohort of 1191 individuals not on thyroxine or antithyroid medication. All participants were aged 60 years or older. We measured concentration of thyrotropin in serum at baseline in 1988-89. We recorded vital status on June 1, 1999, and ascertained causes of death for those who had died. We compared data for causes of death with age-specific, sex-specific, and year-specific data for England and Wales. We also compared mortality within the cohort according to initial thyrotropin measurement.

RESULTS

During 9733 person-years of follow-up, 509 of 1191 people died, the expected number of deaths being 496 (standardised mortality ratio [SMR] 1.0, 95% CI 0.9-1.1). Mortality from all causes was significantly increased at 2 (SMR 2.1), 3 (2.1), 4 (1.7), and 5 (1.8) years after first measurement in those with low serum thyrotropin (n471). These increases were largely accounted for by significant increases in mortality due to circulatory diseases (SMR 2.1, 2.2, 1.9, 2.0, at years 2, 3, 4, and 5 respectively). Increases in mortality from all causes in years 2-5 were higher in patients with low serum thyrotropin than in the rest of the cohort (hazard ratios for years 2, 3, 4, and 5 were 2.1, 2.2, 1.8, and 1.8, respectively). This result reflects an increase in mortality from circulatory diseases (hazard ratios at years 2, 3, 4, and 5 were 2.3, 2.6, 2.3, 2.3), and specifically from cardiovascular diseases (hazard ratios at years 2, 3, 4, and 5 were 3.3, 3.0, 2.3, 2.2).

INTERPRETATION

A single measurement of low serum thyrotropin in individuals aged 60 years or older is associated with increased mortality from all causes, and in particular mortality due to circulatory and cardiovascular diseases.

Reversible autonomic dysfunction in hyperthyroid patients affects gastric myoelectrical activity and emptying

The autonomic nervous system (ANS) function in hyperthyroidism has been so far investigated mainly from the cardiovascular point of view. The aim of this study is to show that the ANS dysfunction in hyperthyroidism is also expressed in gastric myoelectrical activity disturbances and gastric emptying disorders and to search for a correlation between the severity of clinical manifestation and free thyroid hormone levels and the degree of the ANS dysfunction. The analyzed group included 50 recently diagnosed patients with hyperthyroidism who were examined twice: before and after 3 months of thyrostatic treatment. Results were compared with those of a sex-, age- and BMI-matched control group of 50 healthy volunteers. The study included: heart rate variability analysis in time and frequency domain, at rest and during a deep-breathing test, surface electrogastrography in preprandial and postprandial periods measured simultaneously with the ultrasound assessment of gastric emptying time by Bolondi method. In patients with hyperthyroidism in comparison with the control group, the following significant differences were observed: a sharp reduction of the high-frequency component and a decrease of heart rate variability, a high incidence of dysrhythmia with dominant bradyarrhythmia, and a delay of gastric emptying. The degree of disorders related to the degree of clinical manifestation of hyperthyroidism's symptoms and free triiodothyronine serum concentration both. All the disorders were functional and disappeared in a stable euthyroidism. To conclude, the ANS dysfunction in hyperthyroidism results not only in withdrawal of vagal inhibitory effect on sinoatrial node, but in impaired mutual neuro-hormonal regulation (decrease of vagal influence) of gastric myoelectrical activity followed by delay of gastric emptying.

Renin-angiotensin system contribution to cardiac hypertrophy in experimental hyperthyroidism: an echocardiographic study

The objective of this study was to evaluate, using echocardiography, the involvement of the renin-angiotensin system (RAS) in left ventricular (LV) hypertrophy development in experimental hyperthyroidism. Thyrotoxicosis was produced by a daily intraperitoneal injection of L-thyroxine (T4), 0.1 mg/kg per day for 15 days in Wistar rats. Control (euthyroid) rats received intraperitoneal daily injection of the thyroxine solvent. Two series of experiments were performed. In the first series, euthyroid (n = 10) and hyperthyroid (n = 14) rats were surgically prepared with a femoral artery catheter. After a 3-day recovery period, blood pressure and heart rate were measured and blood samples were collected in conscious and unrestrained rats. In the second series of experiment, measurement of LV geometry was realized with two-dimensional time-movement echocardiography on the 15th day of treatment in control conditions and after long-term treatment with the angiotensin II type I receptor antagonist valsartan (10 mg/kg per day for 15 days) in both euthyroid and hyperthyroid rats. The dose and duration of T4 treatment was sufficient to induce a significant degree of hyperthyroidism with characteristic features including tachycardia, systolic hypertension, myocardial hypertrophy, hyperthermia, and weight loss. In addition, we measured an increase in free fractions of thyroid hormones, and a threefold increase in plasma renin activity. Echocardiographic examinations in rats revealed a strong correlation between LV weight and echocardiographic LV mass. Hyperthyroid rats exhibited an increased LV mass with a marked increase in the LV end-diastolic posterior wall and septal thickness. Chronic treatment with valsartan prevented this concentric LV hypertrophy (p < 0.01), with full prevention of the LV posterior wall hypertrophy (p < 0.001) and decreased LV septal hypertrophy (p < 0.05). In conclusion, the cardiovascular alterations of hyperthyroidism were reproduced with thyroid hormone injections in rats. Activation of the RAS in hyperthyroid rats was accompanied by increased LV mass. Using valsartan, we demonstrated that the RAS impinged on the LV remodelling in our experimental hyperthyroidism model. A chronic treatment with an angiotensin II type I receptor antagonist prevented the development of the concentric LV hypertrophy associated with thyrotoxicosis.

Endothelial function in patients with hyperthyroidism before and after treatment with propranolol and thiamazol

Hyperthyroidism is associated with a higher incidence of arterial thromboembolism; increasing age, atrial fibrillation, and mitral valve abnormalities are risk factors. However, the contribution of endogenous coagulation parameters is unclear. Because thyroid hormone influences receptor and transcription factors, it can be expected that it will influence proteins involved in coagulation processes synthetised in many cells. Fourteen hyperthyroid patients were studied untreated, after 1 week of treatment with propranolol, and after therapeutic treatment with thiamazol. Fourteen matched controls were used for comparison. On each occasion, endothelial marker proteins, coagulation/fibrinolysis factors, and inflammatory (liver) markers were measured. Excess thyroid hormone was associated with elevated levels of most endothelium-associated proteins. In addition, plasma fibronectin and fibrinogen were increased, while plasminogen was decreased. No evidence was found that hyperthyroidism was associated with coagulation/fibrinolysis activation, or with increased levels of the inflammation markers interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha) or C-reactive protein (CRP). Propranolol treatment only lowered the von Willebrand factor propeptide, and slightly increased plasminogen. Treatment with thiamazol returned all parameters to normal. Hyperthyroidism increased the plasma levels of most endothelial marker proteins, and of some liver-synthetized proteins. No evidence for coagulation/fibrinolysis activation was found. However, it appears that endothelial activation, which is indicative of a procoagulant state, is present in hyperthyroidism. This may explain the association between hyperthyroidism and thromboembolism especially if other risk factors are present. von Willebrand factor II (vWF:Ag-II) levels may be suitable markers to evaluate acute changes in endothelial function because this parameter responds more rapidly to changes in endothelial function than other factors.

Selective modulation of thyroid hormone receptor action

Thyroid hormones have some actions that might be useful therapeutically, but others that are deleterious. Potential therapeutically useful actions include those to induce weight loss and lower plasma cholesterol levels. Potential deleterious actions are those on the heart to induce tachycardia and arrhythmia, on bone to decrease mineral density, and on muscle to induce wasting. There have been successes in selectively modulating the actions of other classes of hormones through various means, including the use of pharmaceuticals that have enhanced affinities for certain receptor isoforms. Thus, there is reason to pursue selective modulation of thyroid hormone receptor (TR) function, and several agents have been shown to have some beta-selective, hepatic selective and/or cardiac sparring activities, although development of these was largely not based on detailed understanding of mechanisms for the specificity. The possibility of selectively targeting the TRbeta was suggested by the findings that there are alpha- and beta-TR forms and that the TRalpha-forms may preferentially regulate the heart rate, whereas many other actions of these hormones are mediated by the TRbeta. We determined X-ray crystal structures of the TRalpha and TRbeta ligand-binding domains (LBDs) complexed with the thyroid hormone analog 3,5,3'-triiodithyroacetic acid (Triac). The data suggested that a single amino acid difference in the ligand-binding cavities of the two receptors could affect hydrogen bonding in the receptor region, where the ligand's 1-position substituent fits and might be exploited to generate beta-selective ligands. The compound GC-1, with oxoacetate in the 1-position instead of acetate as in Triac, exhibited TRbeta-selective binding and actions in cultured cells. An X-ray crystal structure of the GC-1-TRbeta LBD complex suggests that the oxoacetate does participate in a network of hydrogen bonding in the TR LBD polar pocket. GC-1 displayed actions in tadpoles that were TRbeta-selective. When administered to mice, GC-1 was as effective in lowering plasma cholesterol levels as T(3), and was more effective than T(3) in lowering plasma triglyceride levels. At these doses, GC-1 did not increase the heart rate. GC-1 was also less active than T(3) in modulating activities of several other cardiac parameters, and especially a cardiac pacemaker channel such as HCN-2, which may participate in regulation of the heart rate. GC-1 showed intermediate activity in suppressing plasma thyroid stimulating hormone (TSH) levels. The tissue/plasma ratio for GC-1 in heart was also less than for the liver. These data suggest that compounds can be generated that are TR-selective and that compounds with this property and/or that exhibit selective uptake, might have clinical utility as selective TR modulators.

Tachycardia-induced cardiomyopathy secondary to thyrotoxicosis: a young man with previously unrecognized Graves' disease

A young man with previously unrecognized Graves' disease presented with atrial fibrillation and severe low-output heart failure due to dilated cardiomyopathy. The patient's cardiomyopathy resolved and cardiac function recovered shortly after hyperthyroidism and tachycardia were treated during hospitalization. The temporal relationship between heart rate and cardiac function during the recovery period suggests that chronic tachycardia may have been an important cause of his cardiac dysfunction. Thyrotoxicosis seemed to be directly responsible for the development of sustained supraventricular tachycardia in this patient, which then led to tachycardia-induced cardiomyopathy causing severe low-output heart failure. Although relatively infrequent, this etiology should not be overlooked in patients thyrotoxicosis and heart failure. This is the first case in which the time course and the temporal relationship between the control of heart rate and the recovery of cardiac function are illustrated in a thyrotoxic patient.

Thyroid storm presenting as multiple organ dysfunction syndrome

Thyroid storm is a rare disorder characterized by hypertension, hyperthermia, and multiple systems involvement. Early recognition and treatment of thyroid storm are essential in reducing morbidity and mortality from this disorder. We present the case of a patient with an atypical (normothermic, normotensive) presentation of thyroid storm, accompanied by multiple organ dysfunction syndrome, including lactic acidosis and liver dysfunction, both of which are very rare complications. This case highlights both the multiple organ systems that can be involved in thyroid storm and the importance of recognizing atypical presentations of thyroid storm.

Graves' disease and low-output cardiac dysfunction: implications for autoimmune disease in endomyocardial biopsy tissue from eleven patients

Classic high-output thyrotoxic heart disease is generally considered a direct effect of thyroid hormone. In contrast, the cause of the less common low-output heart failure is generally unknown. The aim of this study was to retrospectively evaluate available endomyocardial biopsy tissue from patients with coexistent Graves' disease and idiopathic low-output heart failure and determine whether the biopsy features were consistent with an autoimmune process. The study group consisted of 11 patients whose mean age was 47 years when they were diagnosed with hyperthyroidism and 52 years when diagnosed with cardiac dysfunction. Right ventricular endomyocardial biopsy tissue revealed severe lymphocytic myocarditis in a patient with severe ophthalmopathy and showed borderline myocarditis in a patient without ophthalmopathy. Biopsy tissues from 6 other patients showed appreciable myocyte hypertrophy and interstitial fibrosis, consistent with dilated cardiomyopathy. Two patients had nondiagnostic biopsy specimens, and 1 patient had features suggestive of arrhythmogenic right ventricular dysplasia. In conclusion, for the 11 patients with Graves' disease and unexplained systolic dysfunction, only 2 (18%) had lymphocytic infiltrates consistent with an autoimmune process. Thus, among patients with Graves' disease, most cases of low-output cardiac dysfunction appear to be due to causes other than an active autoimmune inflammatory process.

Myocardial stunning in hyperthyroidism

The cases of two patients with hyperthyroidism and acute left ventricular (LV) dysfunction with segmental wall motion abnormalities resulting in heart failure are reported. Both had electrocardiographic changes mimicking ischemic coronary artery disease. Treatment with antithyroid medications, beta blockers, and angiotensin-converting enzyme inhibitors rapidly restored LV function. The rapid reversibility suggests a role for myocardial stunning, an important entity to recognize in hyperthyroidism since this form of LV dysfunction can be reversed with appropriate treatment.

Atrial fibrillation in the elderly

Atrial fibrillation is the most common sustained arrhythmia seen in clinical practice. Although it occurs in any age patients, its frequency increases with age and is very common in the elderly. Atrial fibrillation causes substantial symptoms and morbidity and is an important cause of thromboembolism and stroke. The two approaches for therapy in those patients with intermittent or persistent atrial fibrillation are (1) maintenance of sinus rhythm with an antiarrhythmic drug or nonpharmacologic therapy, and (2) maintenance of atrial fibrillation with rate control. At the present time there are no data about the best approach and therapy must therefore be individualized.

Isoprenaline can activate the acetylcholine-induced K+ current in canine atrial myocytes via Gs-derived betagamma subunits

1. G protein betagamma subunits activate the acetylcholine-induced potassium current IK,ACh. There is no evidence of specificity at the level of the betagamma subunits. Therefore all G protein-coupled receptors in atrial myocytes should be able to activate IK,ACh. Paradoxically, it is often stated that isoprenaline does not activate IK,ACh. Rationales to explain this negative result include insufficient concentrations of Gs in the atrium or restricted access of Gs-derived betagamma subunits to the IK,ACh channel. We took advantage of a non-specific increase in Gs that results after infection with adenovirus. 2. Adenoviral infection unmasked a 1 microM isoprenaline-induced IK,ACh which was prevented by propranolol. Isoprenaline occasionally activated IK,ACh in uninfected and freshly dissociated atrial myocytes but the effect was larger and more consistent in infected myocytes. 3. Pertussis toxin pretreatment (100 ng ml-1 overnight) did not block the effect of isoprenaline. The effect of isoprenaline became persistent if cells were pretreated with cholera toxin (200 ng nl-1). 4. Signal transduction events distal to adenylyl cyclase were not involved in isoprenaline-induced IK,ACh. Forskolin (10 microM) did not activate IK,ACh. Inhibition of adenylyl cyclase with cytoplasmic application of 300 microM 2'-deoxyadenosine 3'-monophosphate did not prevent the activation of IK,ACh by isoprenaline. 5. Cytoplasmic application of a betagamma binding peptide derived from the C terminus of beta-adrenergic receptor kinase 1 (50 microM) prevented the effect of isoprenaline on IK,ACh. The peptide did not prevent the stimulation of the L-type calcium current by isoprenaline. 6. The results indicate that beta-adrenoceptors can activate IK,ACh in atrial myocytes through the release of betagamma subunits from Gs.

Thyroid hormone regulates expression of shaker-related potassium channel mRNA in rat heart

Effects of thyroid hormones on cardiac function or rhythm have been known; however, the mechanism is still unclear. In the present study examined were effects of triiodethyronine (T3) on voltage-gated potassium channel gene expression in rat heart since the potassium channels were presumed to modulate cardiac functions. The mRNA expression of five voltage-gated potassium channel gene alpha subunits (Kv1.2, Kv1.4, Kv1.5, Kv2.1, and Kv4.2) in heart was examined by ribonuclease protection assay in rats which were treated with T3 or propylthyouracil (PTU). All these genes except Kv1.4 mRNA were apparently expressed in the normal rat heart ventricle. Kv1.2 mRNA expression in ventricle was markedly suppressed by T3-treatment and enhanced by PTU-treatment. Interestingly, upregulation of Kv1.4 mRNA expression and downregulation of Kv1.5 mRNA expression were concomitantly induced in the ventricle by the PTU-treatment. In addition, the downregulation of the ventricular Kv1.5 mRNA expression induced by PTU was restored by T3 replacement. No changes of Kv2.1 and Kv4.2 mRNA expression were observed in the ventricles by the T3- or PTU-treatment. In heart atrium the same findings were observed. Kv1.4 mRNA expression, which was detectable in control rat atrium, also decreased significantly by T3-treatment. In contrast, no changes of Kv1.2, Kv1.4, and Kv1.5 mRNA expression in rat brains were induced by T3-treatment. These findings suggest that thyroid hormone specifically influences mRNA expression of Shaker-related potassium channel genes in rat hearts through a common T3 receptor-mediated regulation at a transcriptional level.

Mortality after the treatment of hyperthyroidism with radioactive iodine

BACKGROUND

Hyperthyroidism affects many organ systems, but the effects are usually considered reversible. The long-term effects of hyperthyroidism on mortality are not known.

METHODS

We conducted a population-based study of mortality in a cohort of 7209 subjects with hyperthyroidism who were treated with radioactive iodine in Birmingham, United Kingdom, between 1950 and 1989. The vital status of the subjects was determined on March 1, 1996, and causes of death were ascertained for those who had died. The data on the causes of death were compared with data on age-specific mortality in England and Wales. The standardized mortality ratio was used as a measure of relative risk, and the effect of covariates on mortality was assessed by regression analysis.

RESULTS

During 105,028 person-years of follow-up, 3611 subjects died; the expected number of deaths was 3186 (standardized mortality ratio, 1.1; 95 percent confidence interval, 1.1 to 1.2; P<0.001). The risk was increased for deaths due to thyroid disease (106 excess deaths; standardized mortality ratio, 24.8; 95 percent confidence interval, 20.4 to 29.9), cardiovascular disease (240 excess deaths; standardized mortality ratio, 1.2; 95 percent confidence interval, 1.2 to 1.3), and cerebrovascular disease (159 excess deaths; standardized mortality ratio, 1.4; 95 percent confidence interval, 1.2 to 1.5), as well as fracture of the femur (26 excess deaths; standardized mortality ratio, 2.9; 95 percent confidence interval, 2.0 to 3.9). The excess mortality was most evident in the first year after radioiodine therapy and declined thereafter.

CONCLUSIONS

Among patients with hyperthyroidism treated with radioiodine, mortality from all causes and mortality due to cardiovascular and cerebrovascular disease and fracture are increased.

Mechanisms of thyroid hormone action. Implications for the clinical manifestation of thyrotoxicosis

Serum thyroid hormone concentrations alone do not explain the variability and severity of the range of symptoms observed in thyrotoxic patients. Despite gaps in our understanding of the links between the clinical manifestations of thyrotoxicosis and the underlying mechanisms, much has been learned. A limited number of markers directly reflect T3 action. The future elucidation of T3 targets that mediate these effects should ultimately lead to additional clinical markers of tissue-specific T3 action. The availability of such tests should allow for more specific treatment of individual patients.

Trace elements in coronary heart disease: Impact of intensified lifestyle modification

Concentrations of 14 trace elements (Bi, Cd, Co, Cs, Cu, Hg, Mn, Pb, Rb, Sb, Sn, Sr, Tl, and Zn) were determined by inductively coupled plasma mass spectrometry (ICP-MS) in 120 whole-blood and 121 plasma samples of 56 patients with angiographically documented coronary heart disease (CHD). One serum and two whole-blood reference materials were analyzed for quality control. At baseline, patients had elevated Co plasma as well as diminished Cu blood concentrations compared to healthy adults. The Zn concentrations in whole blood were below or at the lower end of the normal range, but the concentrations in plasma were elevated. All other trace elements were within the normal concentration ranges for healthy adults. After initial investigations, patients were randomly assigned to an experimental group (N = 27) and to a usual care group (N = 29). Experimental group patients were prescribed a lifestyle program that included a low-fat diet and a weekly moderate exercise. Patients were examined at baseline, after 6 and 12 mo for clinical assessment and fasting venous blood samples. No significant time-course changes in concentrations of trace elements in blood and plasma during the clinical treatment in both groups of patients could be observed. The experimental group patients lost weight and had lower blood pressure after 12 mo compared to baseline. The interventional therapy reduced the need for further revascularization procedures.

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.

Thyroid diseases in the elderly

The ageing thyroid is associated with a number of morphological and functional changes, such as decreased serum T3 and mean thyroid-stimulating hormone concentrations, that are to some extent independent of intercurrent non-thyroidal illnesses. All thyroid diseases, including clinical and subclinical hypo- and hyperthyroidism, non-toxic nodular goitre and thyroid cancer, are encountered in the elderly, but their prevalence and clinical expression differ from those observed in younger patients. In the elderly, autoimmune hypothyroidism is particularly prevalent, hyperthyroidism is mainly characterized by cardiovascular symptoms and is frequently due to toxic nodular goitres, and differentiated thyroid carcinoma is more aggressive. The interpretation of thyroid function tests is difficult in old individuals, because of age-associated changes in thyroid function and frequent alterations secondary to non-thyroidal illnesses and/or drugs. Treatment of thyroid disease deserves special attention in old patients because of the increased risk of complications.

Action potential configuration in heart papillary muscles from female rats in different thyroid states

We have studied the effects of thyroidectomy and the in vivo administration of different triiodothyronine (T3) doses in thyroidectomized female rats on electrophysiological properties, measured in vitro, of the anterior and posterior papillary muscle fibers from the right ventricle. In each thyroid state, the action potential duration (APD) measured by stimulating at 1 Hz was shorter for the posterior papillary muscle. APD from both preparations was found significantly lengthened in thyroidectomized animals in comparison to euthyroid controls. APD was shortened owing to treatment of thyroidectomized rats with T3 doses up to 10 micrograms/100 g body weight every second day. Treatment with larger doses of T3 tended to restore the values of APD found for ventricular fibres from both controls and thyroidectomized animals treated with substitutive T3 doses (5 micrograms/100 g body weight every second day). As the stimulation rate was increased from 1 to 5 Hz, APD increased in both preparations of all groups. The changes were of different amounts but the APD difference between the rat groups, which were significant at 1 Hz, remained significant at 5 Hz, while the differences between anterior and posterior preparations were cancelled in animals treated with 50 micrograms of T3 and reversed in those treated with 100 micrograms.

Thyroid hormone stimulates Na(+)-Ca2+ exchanger expression in rat cardiac myocytes

We investigated whether thyroid hormone directly affects Na(+)-Ca2+ exchanger expression in cardiac myocytes. Cultured neonatal rat cardiocytes were prepared from 1-day-old Sprague-Dawley rats. Intracellular Na+ concentration ([Na+]i) in cardiocytes was measured by using the Na(+)-sensitive dye sodium-binding benzofran isophthalate (SBFI). Na(+)-Ca2+ exchanger messenger RNA (mRNA) and protein expression were assayed by Northern and Western blotting, respectively. Triiodothyronine (T3; 10(-8) M) showed no effect on [Na+]i in cardiocytes, whereas ouabain (100 microM) caused a significant increase in [Na+]i from 11.3 +/- 5.0 to 21.8 +/- 5.0 mM. Exposure of cardiocytes to ouabain caused a rapid increase in Na(+)-Ca2+ exchanger mRNA accumulation, with a maximal twofold elevation at 12 h. The ouabain-induced Na(+)-Ca2+ exchanger mRNA accumulation was still observed in the Ca(2+)-free culture medium. On the other hand, exposure of cardiocytes to T3 induced a gradual increase in Na+ exchanger mRNA accumulation, with a maximal threefold increase at 24 h. Even in Na(+)-free medium, T3 still induced a twofold increase in Na(+)-Ca2+ exchanger mRNA accumulation in cardiocytes. Exposure of cardiocytes to T3 for 24-48 h also caused a marked increase in Na(+)-Ca2+ exchanger protein accumulation. In conclusion, thyroid hormone directly increases cardiac Na(+)-Ca2+ exchanger expression, independent of alterations in Na+ mobilization. These findings suggest also that thyroid hormone and Na+ regulate Na(+)-Ca2+ exchanger gene expression through distinct molecular regulatory pathways.

[Severe tricuspid insufficiency as main manifestation of hyperthyroidism]

The cardiac manifestations of the hyperthyroidism (HT) are diverse and frequent. However, sometimes, the initial symptoms are atypical and are difficult to diagnose. We present the case of a patient whose HT began with heart failure secondary to a severe tricuspid regurgitation (IT). This data suggests that when confronted with IT of unclear etiology, a possible HT must be investigated.

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.

Three sudden deaths in men associated with undiagnosed chronic thyroiditis

Three cases of sudden death associated with undiagnosed chronic thyroiditis are described. All were young or middle-aged men who were found dead, and death appeared to have occurred suddenly. Two of them had not previously experienced any serious medical problems, the third suffered from well-controlled Addison's disease. None had been investigated or treated for thyroid disease previously. Microscopically all showed a severe chronic thyroiditis with parenchymal destruction and reactive hyperplasia of the acinar epithelium. In the first case elevated triiodothyronin (T3), thyroxin (T4) and low thyroid stimulating hormone (TSH) were present, in the second case low T3 and T4 and normal TSH, and in the third an isolated elevation of T3 were found. Anti-thyroid antibodies were found in two cases. The possible causal relationship between silent chronic autoimmune thyroiditis and sudden death is discussed.

Acute exacerbation of masked hyperthyroidism after iodine restriction followed by thyrotoxic atrial fibrillation and cerebral embolism. A case report

The authors present a seventy-two-year-old woman complaining of diffuse and firm goiter. At the first visit, she looked almost euthyroid with regular pulse rate of 78 per minute. After iodine restriction, however, she became severely thyrotoxic and developed cerebral embolism associated with atrial fibrillation due to Graves' hyperthyroidism. In conclusion, sudden withdrawal of dietary iodine might lead to exacerbation of Graves' hyperthyroidism resulting in serious cardiovascular or cerebrovascular complications, especially in elderly patients.

Congestive cardiac failure in a 65-year-old man

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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.