Excess triiodothyronine as a risk factor of coronary events

Recurrent peri-myocarditis: A rarer but unfortunate redundant presentation of thyroid storm

Thyroid storm represents a critical and life-threatening complication from hyperthyroidism, with a notable mortality risk. Limited literature reports have explored the correlation between thyroid storm and peri-myocarditis, although the precise pathophysiological underpinnings remain unclear. The pathophysiology of how thyroid storm and peri-myocarditis are associated is not clearly understood; however, unfavorable prognostic factors include atrial fibrillation and recurrent thyrotoxicosis. Here, we present a case concerning recurrent peri-myocarditis concomitant with a thyroid storm.

Impending myocardial ischaemia during thyroid storm diagnosed through Wellens' syndrome

We present a case of thyroid storm precipitated by discontinuation of antithyroid drugs. The patient developed a concurrent acute coronary event during the resolution period of the thyroid storm. After 48 hours of prudent management of thyroid storm, the patient's sensorium and haemodynamics were stabilised but he had persistent mild chest discomfort and developed new-onset jaw pain. On admission, ECG showed sinus tachycardia. In consideration of persistent mild chest discomfort and new-onset jaw pain, serial ECGs were performed which revealed biphasic T waves in V2-V3 suggestive of Wellens' syndrome type A. This indicated a critical stenosis of the left anterior descending (LAD) coronary artery and impending myocardial ischaemia. The patient underwent urgent coronary catheterisation, which revealed 80% stenosis of proximal LAD and was subsequently revascularised resolving his symptoms. This case underscores the significance of serial ECG monitoring even after the acute phase of thyroid crisis, which helped in timely identification of Wellens' syndrome.

Effect of Liothyronine Treatment on Quality of Life in Female Hypothyroid Patients With Residual Symptoms on Levothyroxine Therapy: A Randomized Crossover Study

OBJECTIVE

The effects of levothyroxine (LT4)/liothyronine (LT3) combination therapy on quality of life (QoL) in hypothyroid patients former on LT4 monotherapy have been disappointing. We therefore wanted to test the effects of LT3 monotherapy on QoL in hypothyroid patients with residual symptoms despite thyroid stimulating hormone (TSH) values within the reference range.

DESIGN

Female hypothyroid patients with residual symptoms on LT4 monotherapy or combination LT4/LT3 therapy received LT3 and LT4 monotherapy, respectively for 12 weeks in a non-blinded randomized crossover study.

METHODS

Fifty-nine patients aged 18-65 years were included. QoL was assessed using one disease-specific questionnaire (ThyPRO) and two generic questionnaires (Fatigue Questionnaire and SF-36) at baseline and at the end of the two treatment periods. Clinical indices of cardiovascular health (resting heart rate and blood pressure), as well as thyroid tests, were assessed at baseline and at the end of the two treatment periods.

RESULTS

After 12 weeks of LT3 treatment, 12 of the 13 domains of the ThyPRO questionnaire (physical, mental and social domains) showed significant improvements. The most pronounced improvements were less tiredness (mean -21 ± 26; P<0.0001) and cognitive complaints (mean -20 ± 20; P<0.0001). LT4 monotherapy exerted minor effects on two domains only (cognitive complaints and impaired daily life). All three dimensions' scores in the Fatigue Questionnaire (physical, mental and total fatigue) improved after LT3 treatment compared to baseline (P<0.001), and in the SF-36 questionnaire 7 of 8 scales showed significantly better scores after LT3 treatment compared to baseline. There were no differences in blood pressure or resting heart rate between the two treatment groups. TSH in patients on LT3 was slightly higher (median 1.33 mU/L (interquartile range (IQR) 0.47-2.26)) than in patients on LT4 (median 0.61 mU/L (IQR 0.25-1.20; P<0.018). Five patients on LT3 dropped out of the study due to subjectively reported side effects, compared to only one on LT4.

CONCLUSIONS

LT3 treatment improved QoL in women with residual hypothyroid symptoms on LT4 monotherapy or LT4/LT3 combination therapy. Short-term LT3 treatment did not induce biochemical or clinical hyperthyroidism, and no cardiovascular adverse effects were recorded. Further studies are needed to assess the long-term safety and efficacy of LT3 monotherapy.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, identifier NCT03627611.

Graves'-induced prothrombotic state and the risk of early-onset myocardial infarction

Hyperthyroidism represents a state of hypercoagulability and hypofibrinolysis, which predisposes an individual to the increased risk of thromboembolism. We present a case of a 25-year-old patient presenting with an acute myocardial infarction secondary to plaque rupture with thrombotic occlusion of proximal left anterior descending artery, in a patient known to have Graves' disease. She had a sudden ventricular fibrillation arrest and a precordial thump given and cardiopulmonary resuscitation started. She successfully underwent cardiac catheterisation. Subsequent thyroid function tests showed she was in active thyrotoxicosis.

Storm and STEMI: a case report of unexpected cardiac complications of thyrotoxicosis

Background 

Thyroid storm is a rare condition with well-known cardiovascular manifestations including tachycardia, atrial fibrillation, heart failure, and myocardial infarction (MI). Several uncommon conditions that can mimic MI are associated with thyrotoxicosis and discussed in this case.

Case summary 

A 23-year-old previously healthy male presented after the onset of generalized weakness and inability to rise from bed in the setting of 35 kg of unintentional weight loss, and was found to have profound hypokalaemia, elevated thyroid hormone, and suppressed thyroid-stimulating hormone consistent with thyrotoxicosis secondary to Grave’s disease. Following hospital admission, he developed worsening tachycardia with dynamic anteroseptal ST-segment elevations and elevated cardiac biomarkers concerning for MI. He was treated with aspirin, ticagrelor, and a heparin infusion, but was unable to tolerate beta-blockade acutely due to hypotension. Echocardiography demonstrated a severely dilated left ventricle (left ventricular end-diastolic volume index 114 mL/m²) and severely reduced systolic function (ejection fraction 23%) with global hypokinesis. Following initiation of propylthiouracil, iodine solution, and stress-dosed steroids his tachycardia and ST-elevations resolved. Computed tomography (CT) coronary angiography demonstrated no evidence of coronary stenosis. He was discharged on methimazole, metoprolol, and lisinopril and found to have recovered left ventricular systolic function at 2-month follow-up.

Discussion 

Thyrotoxicosis can rarely cause coronary vasospasm, stress cardiomyopathy, and autoimmune myocarditis. These conditions should be suspected in hyperthyroid patients with features of MI and normal coronary arteries. Workup should include laboratory evaluation, electrocardiography (ECG), echocardiography, and non-invasive or invasive ischaemic evaluation.

Impact of Hypothyroidism on Occurrence and Outcome of Acute Coronary Syndrome from the National Inpatient Sample

Thyroid hormones have a profound effect on cardiovascular physiology. We utilized a large national inpatient database in the United States (National Inpatient Sample) to study hypothyroidism in relation to the prevalence of coronary heart disease (CHD) and its impact on outcomes (mortality, the length of stay, and hospitalization cost) in the acute coronary syndrome (ACS) subgroup of CHD patients. We found that although hypothyroidism has an increased association with CHD (odds ratio [OR] 1.11, 95% confidence interval [CI] 1.09 to 1.12, p <0.001), the odds of developing ACS in these CHD patients is lower in the hypothyroid group (OR 0.71, 95% CI 0.70 to 0.72, p <0.001) after adjusting for multiple risk factors. Additionally, patients with hypothyroid ACS have a reduced odds of in-hospital mortality (OR 0.86, 95% CI 0.83 to 0.88, p <0.001), shorter length of stay by 0.45 days (p <0.001), and lower hospitalization cost by $1,531.45 (p <0.001) compared with the euthyroid group. Our findings suggest that hypothyroidism has an increased CHD risk but a lower risk of development of ACS in hospitalized CHD patients, as well as a better short-term prognosis including ACS-associated mortality.

Takotsubo Cardiomyopathy Associated with Levothyroxine Over-replacement

Takotsubo cardiomyopathy (TC) is characterised by acute, transient left ventricular apical ballooning precipitated by emotional or physiologically stressful stimuli and has been previously associated with Grave’s disease based on a few clinical reports. More recently, the association with exogenous thyrotoxicosis and radioiodine-induced thyroiditis has also been described. Iatrogenic hyperthyroidism on patients on levothyroxine replacement therapy for hypothyroidism has not been reported as a cause of TC. The authors describe two female patients with TC associated with levothyroxine over-replacement. A 74-year-old and a 48-year-old female patient, medicated with levothyroxine (respectively, 2.27 μg/kg and 1.85 μg/kg) for autoimmune thyroiditis were admitted to our emergency room with precordial pain. The first had an electrocardiogram with ST-segment elevation in the anterior precordial leads, and the latter had sinus tachycardia with deep T-wave inversion and QT interval prolongation. Further investigation revealed a mild elevation of cardiac biomarker levels and severe apical hypokinesis, but no significant coronary lesions on catheterisation. The suppressed thyroid stimulating hormone (TSH) levels were verified in the cardiac intensive care unit: 0.21 and 0.07 mIU/l (0.35–5.50) respectively. Both patients showed improvement of the apical hypokinesis on the discharge echocardiogram and normalisation of cardiac biomarker levels. Levothyroxine dose was reduced. This case report focuses on the cardiovascular risks of thyrotoxicosis, emphasises the importance of correct dose adjustment on patients under levothyroxine replacement therapy and stresses that TSH should be determined in patients presenting with acute coronary syndrome and typical findings of TC.

Recommendations for treatment of hypothyroidism with levothyroxine and levotriiodothyronine: a 2016 position statement of the Italian Society of Endocrinology and the Italian Thyroid Association

Levothyroxine (L-T4) is recommended as lifelong replacement therapy for hypothyroidism. Recent clinical and experimental data support the addition of levotriiodothyronine (L-T3) treatment in some selected hypothyroid patients when their symptoms persist and their quality of life remains impaired despite adequate L-T4 monotherapy. An increase in L-T3 prescriptions has been recently observed in Italy due to availability of different L-T3 formulations, making it possible to clinicians to prescribe L-T3 alone or in combination with L-T4. The aim of the present position statement was to define the correct clinical indications, schedule, duration of treatment and contraindications of combined treatment with L-T4 and L-T3 in hypothyroid patients in an attempt to guide clinicians and to avoid potential adverse effects of overtreatment.

Signal peptide-CUB-EGF domain-containing protein 1 (SCUBE1) levels in patients with overt and subclinical hyperthyroidism: effects of treatment

BACKGROUND AND OBJECTIVES

Signal peptide-CUB-EGF domain-containing protein 1 (SCUBE1) has been shown to increase in parallel with platelet activation in acute ischaemic and thrombotic diseases. There has been no study evaluating SCUBE1 levels in patients with overt hyperthyroidism (OHyper) and subclinical hyperthyroidism (SHyper), conditions which are known to show impairment of both endothelial and platelet function. This study sought to evaluate SCUBE1 concentrations in patients with SHyper and OHyper, and assessed the effects of antithyroid drug (ATD) therapy on circulating SCUBE1 levels.

DESIGN AND METHODS

Forty-five untreated patients with OHyper, 20 untreated patients with SHyper and 30 age- and sex-matched healthy controls were prospectively included in the study. Biochemical and hormonal parameters were evaluated in all patients before and after treatment.

RESULTS

Compared with the control subjects, SCUBE1 levels were significantly increased in patients with SHyper and OHyper (P < 0·0001 and P = 0·002, respectively). SCUBE1 levels were not significantly different in patients with OHyper compared with patients with SHyper. There was no significant correlation between serum thyroid hormones and SCUBE1 levels. Plasma SCUBE1 levels decreased significantly in both OHyper and SHyper after ATD treatment (P < 0·05).

CONCLUSIONS

Increased SCUBE1 levels in both SHyper and OHyper patients may reflect increased platelet activation and possible endothelial dysfunction, which might augment the risk for atherosclerotic and atherothrombotic complications. SCUBE1 may be used as a reliable marker of endothelial damage in hyperthyroidism, especially in the subclinical period.

Severe Hyperthyroidism Presenting with Acute ST Segment Elevation Myocardial Infarction

Introduction. Acute myocardial infarction is life-threatening. A cardiac troponin rise accompanied by typical symptoms, ST elevation or depression is diagnostic of acute myocardial infarction. Here, we report an unusual case of a female who was admitted with chest pain. However, she did not present with a typical profile of an acute myocardial infarction patient. Case Presentation. A 66-year-old Han nationality female presented with chest pain. The electrocardiogram (ECG) revealed arched ST segment elevations and troponin was elevated. However, the coronary angiography showed a normal coronary arterial system. Thyroid function tests showed that this patient had severe hyperthyroidism. Conclusion. Our case highlights the possibility that hyperthyroidism may cause a large area of myocardium injury and ECG ST segment elevation. We suggest routine thyroid function testing in patients with chest pain.

Association of Thyroid Function with Severity of Coronary Artery Disease in Euthyroid Patients

INTRODUCTION

Thyroid hormone exerts multiple effects on the heart and vascular system. Variations of free T3 have been linked to coronary artery disease. We conducted a study to observe whether there is a relationship between the variation of the serum thyroid hormone levels (TSH, FT3 and FT4) and the presence and severity of CAD in the euthyroid patients.

AIM

To study association of serum TSH, FT4 and FT3 levels within the normal range with presence and severity of coronary artery disease.

MATERIALS AND METHODS

A total of 100 euthyroid patients with stable angina, who underwent coronary angiography were enrolled in the study. Coronary artery disease was defined as >50% stenosis in the luminal diameter in at least one major epicardial coronary artery. The Gensini scoring system was used to define the severity of the CAD and serum TSH, FT3 and FT4 levels were measured by the chemiluminescence method.

RESULTS

Single vessel disease was found in 23%, double vessel disease in 15% and triple vessel disease in 17% of patients. TSH and FT4 levels were also comparable between the groups. Normal coronary group had significantly higher mean FT3 values than triple vessel disease (p=0.004) and FT3 levels showed an inverse relation with Gensini score (Pearson's correlation =- 0.30) (p =0.002). A level of FT3 ≤ 2.7 predicted the severity of CAD with a 70% sensitivity and 60% specificity (area under curve (AUC): 0.755, p=0.001).

CONCLUSION

In the absence of primary thyroid disease and acute coronary syndrome, the occurrence of CAD is associated with lower serum levels of FT3. FT3 and not the FT4 and TSH levels may be used as an indicator of increased risk for severe CAD. The present study clearly shows the existence of a strong association between the reduction of biologically active T3 and severity of coronary artery disease. However, low T3 state could be at first interpreted as just a biological risk factor of severe coronary artery disease; only the demonstration of beneficial effects on cardiovascular, end points of long term T3 replacement in CAD patients with low T3 state can answer this fundamental issue.

Ischemia-modified albümin and malondialdehyde levels in patients with overt and subclinical hyperthyroidism: effects of treatment on oxidative stress

The main purpose of this study was to evaluate the levels of ischemia-modified albumin (IMA) and malondialdehyde (MDA) in patients with OHyper and SHyper, to assess the effects of antithyroid drug (ATD) therapy on the oxidative stress (OS) parameters. Forty-five untreated patients with overt hyperthyroidism (OHyper), 20 untreated patients with subclinical hyperthyroidism (SHyper) and 30 age-and sex-matched healthy controls were prospectively included in the study. Biochemical and hormonal parameters were evaluated in all patients before and after treatment. Compared with the control subjects, the levels of MDA, glucose and TG were significantly increased in patients with SHyper (p<0.05), whereas LDL-C levels were significantly decreased (p<0.01). Patients with OHyper showed significantly elevated MDA and glucose levels (p<0.001) and significantly decreased LDL-C and HDL-C levels compared with the controls (p<0.01). In patients with Graves' disease, serum TSH levels were inversely correlated with plasma MDA levels (r: -0.42, p<0.05). Plasma MDA levels significantly decreased and levels of TC, LDL-C and HDL-C significantly increased in the groups of OHyper and SHyper after treatment. Serum IMA levels did not significantly change at baseline and with the therapy in all subjects. In conclusion, increased MDA levels in both patient groups represent increased lipid peroxidation which might play an important role in the pathogenesis of the atherosclerosis in these patients. Increased oxidative stress in patients with SHyper and OHyper could be improved by ATD therapy. Also, MDA can be used as a reliable marker of OS and oxidative damage, while IMA is considered to be inappropriate.

The role of serum C-reactive protein measured by high-sensitive method in thyroid disease

The aim of this study was the evaluation of serum C-reactive protein (CRP) concentration as a marker of the inflammatory state in many different thyroid diseases and its dependence on the stage and duration of disease. We conducted a retrospective analysis of 444 randomly selected patients with different kinds of thyroid disease (106 men and 338 women, ranging 18-72 years of age; mean 56.2 ± 5.0 years; median 52 years). Group 1 (G1) comprised 250 patients with hyperthyroidism. Group 2 (G2) consisted of 72 euthyroid patients. Group 3 (G3) consisted of 122 patients with hypothyroidism. Free T4, free T3, and thyrotropin (TSH) levels were measured using the electrochemiluminescent method. Human serum thyroglobulin autoantibodies (Tg-Abs), thyroperoxidase autoantibodies (TPO-Abs), and autoantibodies against the thyrotropin receptor (TSHR-Abs) levels were measured by radioimmunoassay. The high-sensitive CRP (Hs-CRP) level (reference range <3 mg/L) was determined with a highly sensitive latex-based immunoassay. The mean value of Hs-CRP in G1 was 3.6 ± 2.8 mg/L, in G2 2.5 ± 1.5 mg/L and in G3 5.9 ± 5.8 mg/L. Hs-CRP (in mg/L) medians, interquartile and the total ranges in G1 were 3.0 (2.0 [0.1-21.0] 4.0); in G2: 2.3 [1.8 (0.2-9.2) 3.2]; and in G3: 4.3 [2.2 (0.3-31.5) 7.8]. We found statistically significant differences (Kruskal-Wallis test) in serum Hs-CRP values between G1 and G2 (P = 0.007), G1 and G3 (P = 0.001), G2 and G3 (P < 0.001). In G1, statistically significant correlation was confirmed between Hs-CRP and Tg-Abs (r = -0.22, P = 0.0016), CRP and TPO-Abs (r = -0.26, P < 0.001), and also between Hs-CRP and TSHR-Abs (r = -0.18, P = 0.02). In the remaining cases, differences between Hs-CRP and TSH levels (r = -0.09, P = 0.16) were not statistically significant. In G2, no statistically significant correlation was observed: Hs-CRP and Tg-Abs (r = -0.18, P = 0.13), Hs-CRP and TPO-Abs (r = -0.17, P = 0.15), Hs-CRP and TSH (r = 0.01, P = 0.91), Hs-CRP and TSHR-Abs (r = -0.19, P = 0.17). In G3, a statistically significant correlation was confirmed between Hs-CRP and Tg-Abs (r = 0.22, P = 0.012), Hs-CRP and TSH (r = -0.28, P = 0.001). No statistically significant correlation was observed between Hs-CRP and TPO-Abs (r = 0.20, P = 0.06) and between Hs-CRP and TSHR-Abs (r = -0.23, P = 0.11). Hs-CRP is increased in various types of hypothyroidism. This is particularly relevant in postpartum thyroiditis and in patients after radioiodine treatment. The impact of this situation on human health requires further research, however, one might assume that some types of thyroid disease may lead to systemic inflammatory reactions that are reflected in elevated CRP levels.

Triiodothyronine and free thyroxine levels are differentially associated with metabolic profile and adiposity-related cardiovascular risk markers in euthyroid middle-aged subjects

BACKGROUND

We have previously shown that in healthy young men, a less favorable body composition is associated with higher free triiodothyronine (fT3) levels within the euthyroid range. Besides, a higher free-triiodothyronine-to-free-thyroxin (fT3-to-fT4) ratio has been related to a less favorable metabolic phenotype and more placental growth in pregnant women. In the present study, we therefore investigated whether serum thyrotropin (TSH), thyroid hormone levels, and the fT3-to-fT4 ratio are associated with metabolic and adiposity-related cardiovascular risk markers in a healthy population of middle-aged euthyroid men and women.

METHODS

Thyroid parameters were measured in 2524 generally healthy subjects from the Asklepios Study (35-55 years, mean age 46 years). Analyses were restricted to 2315 subjects (1138 women and 1177 men), not using thyroid medication, not having anti-TPO levels above clinical cutoff values or TSH levels outside the reference range (0.27-4.2 mU/L). Twenty-seven percent of the women and 47.5% of the men were overweight, while 13% of women and 17% of men were obese. Twenty percent of the subjects were active smokers. Serum thyroid function parameters were determined by electrochemiluminescence.

RESULTS

fT3 and the fT3-to-fT4 ratio were positively related to body mass index (BMI), waist circumference, and components of metabolic syndrome, that is, triglycerides, systolic and diastolic blood pressure, and fasting plasma glucose, and negatively with HDL-cholesterol levels, whereas fT4 was negatively associated with BMI, waist circumference, and triglycerides (p<0.001). TSH related positively with total cholesterol levels (p<0.01), triglycerides, and systolic and diastolic blood pressure (p<0.001). The fT3-to-fT4 ratio was further positively associated with the adiposity-related inflammation markers interleukin-6 and high-sensitivity C-reactive protein and to pulse wave velocity. All associations were adjusted for sex, age, height, and smoking, and most associations persisted after additional adjustment for weight or waist circumference.

CONCLUSION

In healthy euthyroid middle-aged men and women, higher fT3 levels, lower fT4 levels, and thus a higher fT3-to-fT4 ratio are consistently associated with various markers of unfavorable metabolic profile and cardiovascular risk.

Combination L-T3 and L-T4 therapy for hypothyroidism

PURPOSE OF REVIEW

Because of the longstanding controversy regarding whether hypothyroid patients can be optimally replaced by treatment with levothyroxine (L-T4) alone, numerous studies have addressed potential benefits of combined therapy of triiodothyronine (T3) with L-T4. Results of these studies have failed to support a potential benefit of combined therapy. A strong argument for the addition of L-T3 to L-T4 monotherapy has been lacking until recent genetic studies indicated a rationale for such therapy among a small fraction of the hypothyroid patient population.

RECENT FINDINGS

Interest in this issue has focused on the importance of the deiodinases in maintaining the euthyroid state and the role of genetic polymorphisms in the deiodinase genes that would affect thyroid hormone concentrations in both blood and tissues. One such polymorphism in the D2 gene, Thr92Ala, is associated with reduced T4 to T3 activation in skeletal muscle and thyroid, linked to obesity and alterations in thyroid-pituitary feedback, and in responses to thyroid hormone treatment.

SUMMARY

Although our professional organizations continue to recommend L-T4 alone for the treatment of hypothyroidism, the possibility of a D2 gene polymorphism should be considered in patients on L-T4 monotherapy who continue to complain of fatigue in spite of dosage achieving low normal serum thyroid stimulating hormone levels. A suggestive clue to the presence of this polymorphism could be a higher than normal free T4/free T3 ratio. Clinicians could consider adding T3 as a therapeutic trial in selected patients. Future well controlled clinical trials will be required to more fully resolve the controversy.

The relationship between thyroid stimulating hormone within the reference range and coronary artery disease: impact of age

Studies on the relationship between thyroid stimulating hormone (TSH) within the reference range and coronary artery disease (CAD) have produced conflicting results. Furthermore, the effect of age on this relationship has never been explored. The aim of this study was to investigate the association between TSH levels and CAD among euthyroid subjects and whether age influenced this relationship. A total of 318 subjects who underwent coronary angiography were included. Serum TSH, T3, T4, lipid, blood glucose and creatinine levels were measured and compared between the groups with and without CAD. Age-stratified analysis and multivariate logistic regression analysis were performed. Levels of TSH, T3 and T4 did not differ significantly between CAD (n=196) and non-CAD group (n=122) (TSH: 1.77 ± 0.99 vs 1.89 ± 0.98 mIU/L, T3: 1.45 ± 0.36 vs 1.51 ± 0.35 nmol/L, T4: 100.06 ± 20.49 vs 103.95 ± 24.06 nmol/L, respectively) when comparisons were performed among all subjects. A significant between-group difference in levels of TSH was observed among subjects less than or equal to 65 years old (CAD group: n=121, non-CAD group: n=106), with higher TSH levels in CAD group (2.03 ± 0.94 vs 1.75 ± 0.97 mIU/L, adjusted p=0.024). Multivariate logistic regression analysis revealed that elevated level of TSH was an independent predictor for CAD (odds ratio: 1.512, p=0.011). No significant between-group difference in TSH levels was observed among subjects older than 65 years (CAD group: n=75, non-CAD group: n=16). The results showed that higher levels of TSH within the reference range were independently associated with the presence of CAD only among subjects less than or equal to 65 years old, suggesting age might influence the relationship.

Subclinical hyperthyroidism and the risk of cardiovascular events and all-cause mortality: an updated meta-analysis of cohort studies

OBJECTIVES

Whether subclinical hyperthyroidism (SCH) results in poor prognosis remains controversial. Our aim was to evaluate the association between SCH and the risk of cardiovascular disease (CVD), cardiovascular mortality, and all-cause mortality by conducting a meta-analysis of cohort studies.

METHODS

The PubMed and Embase databases were searched through November 2011 to identify studies that met pre-stated inclusion criteria. Relevant information for analysis was extracted. Either a fixed or a random effects model was used to calculate the overall combined risk estimates.

RESULTS

Seventeen cohort studies were included in this meta-analysis. The overall combined relative risks for individuals with SCH compared with the reference group were 1.19 (95% confidence interval (CI): 1.10 to 1.28) for CVD, 1.52 (95% CI: 1.08 to 2.13) for cardiovascular mortality, and 1.25 (95% CI: 1.00 to 1.55) for all-cause mortality. Subgroup analysis by sample source (community or convenience sample) showed that the significant association for cardiovascular and all-cause mortality only existed when pooling studies from convenience samples. Heterogeneity was observed when pooling studies on the association between SCH and cardiovascular and all-cause mortality. Sensitivity analysis showed omission of each individual study did not significantly change the pooled effects. No evidence of publication bias was observed.

CONCLUSIONS

Our findings demonstrated that SCH significantly increased the risk of CVD for the general population and the risk of cardiovascular and all-cause mortality for the individuals with other morbidities.

Vasospastic angina in a patient with hyperthyroidism

A 56-year-old man presented with typical angina pectoris lasting >20 min associated with precordial ST-segment elevation. Urgent coronary angiography showed critical stenosis in the proximal segment of the left anterior descending artery, which resolved with intracoronary nitrate application. He was subsequently diagnosed with hyperthyroidism secondary to exposure of iodinated contrast agent which is thought to be the cause of the coronary spasm. Symptoms resolved upon treatment with propylthiouracil, slow-release diltiazem, isosorbide mononitrate, and aspirin. This unusual case highlights the importance of considering hyperthyroidism in the differential diagnosis of chest pain and coronary artery spasm. We suggest routine thyroid function testing in patients with coronary spasm.

Acute myocardial infarction as the first presentation of thyrotoxicosis in a 31-year old woman - case report

A 31-year old woman, previously fit & well was admitted with pressing retrosternal chest pain and palpitations of sudden onset. Her body weight was normal (BMI 20.5 kg/m²) and there was no significant family history of cardiac disease. She smoked, however, about 15 cigarettes a day and she had been taking combined oral contraceptive pill (Cilest^®) for about three years. On admission she appeared sweaty and in pain, blood pressure 130/70 mmHg, heart rate about 110/min, mild lid-lag sign. Heart sounds were normal and chest was clear. ECG revealed 2-3 mm ST segment elevations in II, III, aVF as well as V2 to V5. Troponin I was raised and she was qualified to an emergency coronary angiography. This revealed a massive spasm of left anterior descending (LAD) coronary artery that responded to intracoronary glyceryl trinitrite administration, however, with the presence of critical narrowing of the LAD apical segment with possible superimposed thrombus. Cardiac ultrasound revealed akinesis of 1/2 of apical area consistent with myocardial infarction

Treatment and progress

She was started on Aspirin, Simvastatin, and Diltiazem, but continued to have persistent tachycardia and tremor. Thyroid function tests were ordered and showed thyrotoxicosis [free T4-46.9 pmol/l (ref. range 9-25), free T3-11.9 pmol/l (2-5), TSH - 0.02 mIU/l (0.27-4.2)]. She was referred for an endocrine opinion and started on Thiamazole. Other investigations revealed elevated anti-TPO and anti-TSH receptor antibodies consistent with Graves' disease. Thrombophilia screen was negative. She had remained euthyroid on a "block & replace" regimen (Thiamazole plus L-Thyroxine) that was discontinued after 18 months. She denies any anginal symptoms, but continues to smoke against medical advice.

Conclusions

Our case highlights the possibility of development of an acute myocardial infarction in a young subject with thyrotoxicosis. We speculate that patient's smoking habit combined with subtle thyrotoxicosis-induced prothrombotic state and/or coronary-artery spasm had lead to the above-mentioned acute coronary event.

Higher serum free thyroxine levels are associated with coronary artery disease

Thyroid hormone has many effects on the heart and cardiovascular system. Thyrotoxicosis is associated with increased cardiovascular morbidity and mortality, primarily due to heart failure and thromboembolism. However, the relationship between thyroid hormone excess and the cardiac complications of angina pectoris and myocardial infarction remains largely speculative. Moreover, few studies have been reported on the effect of thyroid hormone levels within normal range on coronary artery disease (CAD). Therefore we examined the association of thyroid function with coronary artery diseases in euthyroid angina patients. Total 192 subjects (mean age; 60.8 yrs) were enrolled in which coronary angiograms were performed due to chest pain. We measured free thyroxine (FT(4)), thyroid stimulating hormone (TSH), serum lipid levels and high-sensitivity C-reactive protein (hsCRP) levels and analyzed their association with the presence of CAD. Serum FT(4) levels were higher in patients with CAD compared with the patients without CAD (1.31 +/- 0.30 vs 1.20 +/- 0.23, p = 0.006), and high FT(4) level was associated with the presence of multi-vessel disease. Multivariate analysis showed that age (odds ratio (OR) 1.04; 95% confidence interval (CI) 1.01-1.07, p = 0.007), hypertension (OR 2.04; 95% CI 1.06-3.90, p = 0.036) and FT(4) (OR 4.23; 95% CI 1.12-15.99, p = 0.033), were the determinants for CAD. The relative risk (RR) for CAD in highest tertile of FT(4) showed increased risk compared with the lowest tertile (RR 1.98; 95% CI 0.98-3.99, p<0.001). Our study showed that FT(4) levels were associated with the presence and the severity of CAD. Also, this study suggests that elevated serum FT(4) levels even within normal range could be a risk factor for CAD. Further studies will be necessary to confirm the relationship of thyroid function and CAD.

Altered platelet plug formation in hyperthyroidism and hypothyroidism

OBJECTIVE

Patients with thyroid diseases have abnormalities of blood coagulation including an alteration of von Willebrand factor (vWF) levels. Because vWF plays an important role in primary hemostasis, we hypothesized that heightened and decreased vWF levels in hyper- and hypothyroidism enhance and decrease platelet plug formation, respectively.

METHODS

We followed a cohort of 120 patients with overt hyperthyroidism, patients with subclinical and overt hypothyroidism, and euthyroid controls. vWF and in vitro platelet plug formation as collagen-epinephrine-induced closure time (CEPI-CT) were measured at baseline and during therapy with thiamazole or T(4).

RESULTS

Baseline vWF levels were higher in patients with hyperthyroidism and lower in patients with overt hypothyroidism than in controls (P < 0.01). High vWF antigen levels were associated with increased baseline platelet plug formation in patients with hyperthyroidism as compared with controls [114 sec (95% confidence interval, 105-122 sec) vs. 130 sec (120-140 sec), P = 0.01]. After 8 wk of therapy with thiamazole, serum concentrations of T(4) and vWF levels decreased to normal values (P < 0.01 vs. baseline), and CEPI-CT was prolonged as compared with baseline (P < 0.01). During therapy with T(4), vWF levels increased (P < 0.05 vs. baseline) and CEPI-CT was shortened as compared with baseline (P < 0.01).

CONCLUSION

Hyperthyroidism-induced vWF elevation is associated with enhanced platelet function and therefore shortened CEPI-CT values. These changes may contribute to the higher risk for cardiovascular disease in patients with hyperthyroidism. Platelet plug formation decreases during therapy with thiamazole. Furthermore, CEPI-CT appears to be sensitive to detect acquired von Willebrand disease associated with overt hypothyroidism.

Thyroid hormone use, hyperthyroidism and mortality in older women

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Hyperthyroidism affects arterial stiffness, plasma NT-pro-B-type natriuretic peptide levels, and subendocardial perfusion in patients with Graves' disease

BACKGROUND

Arterial stiffness is thought to play a critical role in the pathogenesis of cardiovascular events, and in hyperthyroidism increased cardiovascular event rates have been reported.

AIM

To investigate markers of systemic arterial stiffness, volume homeostasis, and subendocardial perfusion and its interrelationship in patients with Graves' disease (GD) in hyperthyroidism and euthyroidism.

METHOD

Aortic augmentation index (AIx@75) as a measure of systemic arterial stiffness and subendocardial viability ratio (SEVR) as a surrogate measure of subendocardial perfusion were assessed by applanation tonometry in 59 patients with GD in hyperthyroidism and euthyroidism, and measurements were compared to plasma levels of NT-pro-B-type natriuretic peptide (NT-ProBNP).

RESULTS

AIx@75 and NT-ProBNP levels were significantly increased in hyperthyroidism compared to euthyroidism and were positively correlated with each other. SEVR was significantly decreased in hyperthyroidism compared to euthyroidism, mainly due to increased heart rates as shown by the heart rate-corrected SEVR75.

CONCLUSIONS

In hyperthyroidism, patients with GD exhibited increased systemic arterial stiffness, paralleled by increased levels of NT-ProBNP, a marker of volume overload. The decreased subendocardial perfusion in hyperthyroidism seemed to be mainly due to increased heart rates. The observed unfavorable hemodynamic alterations in hyperthyroidism may serve to explain increased cardiovascular event rates in patients with GD.

Lower serum free thyroxine levels are associated with metabolic syndrome in a Chinese population

Thyroid hormones play an important role in regulating energy homeostasis and lipid and glucose metabolism. This study assessed the relationship between free thyroxine and clinical features of metabolic syndrome (MS). A total of 4,938 Taiwanese subjects (2,891 men and 2,047 women with a mean age of 50.1+/-12.6 years) with normal serum free thyroxine levels were enrolled. A modified National Cholesterol Education Program definition of MS was adopted substituting body mass index (BMI) for waist circumference. Serum free thyroxine concentrations were determined by immunoassay. Overall, 14% of subjects had a high fasting glucose, 27% had high blood pressure, 14% had high serum total triglyceride, 8% had low high-density lipoprotein cholesterol, and 18% were obese. The serum free thyroxine concentrations showed a statistically significant correlation with triglyceride and body mass index, respectively (P<.01), but not with blood pressure, glucose level, or high-density lipoprotein cholesterol level. According to the presence of 0, 1, 2, and 3 or more features of MS, age and sex-adjusted means of serum free thyroxine were 17.8+/-3.7, 17.6+/-3.7, 17.5+/-3.7, and 17.1+/-3.3 pmol/L, respectively, with a modest, but statistically significant, decreasing trend (P<.05). When comparing subjects in the highest and lowest quartile of free thyroxine, the former group demonstrated a 2-fold decrease in the odds ratio for MS with 3 or more metabolic features. Low circulating free thyroxine levels, albeit normal, were associated with MS in a Chinese population. Further study is necessary to document the role of thyroid hormones in metabolic abnormalities of MS.

Severe coronary artery spasm can be associated with hyperthyroidism

BACKGROUND

Coronary artery spasm is not infrequently seen in Korea. Most of the patients with coronary spasm show a focal spasm in coronary angiography. However, the cause of the disease is not well known. There have been a few anecdotal case reports of coronary artery spasm associated with hyperthyroidism, but there has not been a report concerning a large series of such patients. Over a period of 5 years and 8 months, we experienced eight patients having the diffuse or severe type of coronary artery spasm in association with hyperthyroidism.

METHODS

We investigated the characteristics of the patients with coronary artery spasm, which was diagnosed by coronary angiography or by provocation with an intracoronary injection of acetylcholine or ergonovine. The demographic data, coronary angiographic findings, thyroid function test results, and the follow-up clinical data of the eight patients having coronary artery spasm associated with hyperthyroidism were analyzed.

RESULTS

All eight patients had Graves' disease. In six patients, the coronary arterial vasoconstriction developed during the coronary angiography without an injection of ergonovine. In three patients, the left main stem coronary artery was involved in the spasm. Among these eight patients, five were female, and all of these female patients were < or = 51 years old. All of the patients were treated with anti-thyroid medications, calcium channel blockers, and long-acting nitroglycerines; they all remained free of chest pain during the median follow-up period of 5 years.

CONCLUSIONS

A severe form of coronary artery spasm could be associated with hyperthyroidism. A high level of suspicion and the thyroid function study should be mandatory for patients with coronary artery spasm, especially for the young female patients.

Manifestations et risques cardiovasculaires des dysthyroïdies infracliniques

PURPOSE

To clarify the importance of cardiovascular symptoms and risks in subclinical dysthyroidism in order to define the best way of treatment and follow-up.

CURRENT KNOWLEDGE AND KEY POINTS

Subclinical dysthyroidism is defined by abnormal circulating TSH values in face and normal free thyroid hormones levels, in asymptomatic individuals. If the cardiovascular effects of overt hyperthyroidism are well documented, the relation between subclinical dysthyroidism and the heart is not well established. Subclinical hyperthyroidism may be caused by the same thyroid disorders that results in overt hyperthyroidism, but the most common cause is excessive dosage in levothyroxine. The most frequent cardias complication of subclinical hyperthyroidism is atrial fibrillation. Recently minimal alterations of myocardial function have also been described. In most patients, one tries to return to euthyroidism in order to prevent cardiovascular complications. Subclinical hypothyroidism is 3 to 10 times more frequent, especially in women after 60 years. Subtle modifications of cardiac function and lipid metabolism and an increased risk of atherosclerosis have been described in this condition. There is still debate about the decision to treat or not to treat these patients.

FUTURE PROSPECTS AND PROJECTS

Until now, treatment of subclinical dysthyroidism is mainly based upon experiences and convictions to physicians. Prospective studies are necessary to assess the true benefits and risks of either early treatment or therapeutic abstention with regular clinical and biological follow up. In such studies, patients should be separated according to age and the nature (endogenous or exogenous) of dysthyroidism.

Differentiated thyroid carcinoma in childhood and adolescence-clinical course and role of radioiodine

BACKGROUND

Differentiated thyroid carcinoma (DTC) in childhood has a good prognosis despite a high incidence of relapse. The use of radioactive iodine (RAI) has not been well established.

PROCEDURE

This is a review of 60 patients less than 21 years of age; mean follow-up was 14 years.

RESULTS

Patients had a higher relapse rate with papillary thyroid carcinoma (PTC) than with follicular thyroid carcinoma (FTC): 24.5 vs. 9.1%. Compared with 997 patients with age > or = 21, patients <21 years of age had a higher female to male ratio (7.6 vs. 3.9), higher incidence of nodal metastasis (45 vs. 28%), and lung metastasis (15 vs. 7.8%), and improved 10-year cause-specific survival (CSS) (98.3 vs. 89.5%). The 10-year rates of CSS, local-regional failure-free survival (LRFFS), and distant metastasis failure-free survival (DMFFS) for the young patients were 98.3, 79.3, and 90.7%, respectively. In patients with no distant metastasis at presentation, RAI improved 10-year LRFFS (71.9 vs. 86.5%; P = 0.04). At last follow-up, 10 of 12 patients (80%) with local-regional (LR) relapse and five of nine patients (55.6%) with distant metastasis were rendered disease-free. No patient has experienced a second malignancy.

CONCLUSIONS

Prognosis of DTC in young patients was good. Patients with LR relapse and distant metastasis had a high rate of remission after treatment. RAI treatment can reduce the rate of LR relapse in patients with no distant metastasis and result in complete remission in half of those with distant metastasis. No patient experienced a second malignancy.

Thyroid disease

Evaluation and treatment of thyroid disease is a common feature of primary care medicine. Nevertheless, the dose of thyroid hormone used to treat hypothyroidism is frequently not titrated to normalize the TSH, engendering the risks of under- or overtreatment. Other hypothyroid patients remain symptomatic even with normalized TSH on levothyroxine alone. Some of these patients improve symptomatically when liothyronine is added to the treatment regimen. Subclinical hypothyroidism and hyperthyroidism are also relatively common in primary care medical practice, and appropriately selected patients probably benefit from treatment. In the follow-up of patients treated for thyroid cancer, the use of rhTSH improves patient comfort considerably while allowing sensitive screening for persistent or recurrent cancer.

Changes in Clinical Presentation, Management and Outcome in 1348 Patients with Differentiated Thyroid Carcinoma: Experience in a Single Institute in Hong Kong, 1960–2000

The clinical features, management and outcome of 1348 patients diagnosed with differentiated thyroid carcinoma in Queen Elizabeth Hospital, Hong Kong, were analysed according to the period of diagnosis: A (before 1980), B (1981-1990) and C (1991-2000). As time advanced, ratio of papillary carcinoma (PTC) to follicular carcinoma (FTC) increased (A:B:C = 1.6: 3.1: 7.2). The mean size of the primary tumour decreased (A:B:C = 3.5 cm: 2.8 cm: 2.5 cm), with a greater percentage of microcarcinoma of 1 cm or less (A:B:C = 5.1%: 16.1%: 21.7%). At presentation, the incidence of lymph-node metastasis decreased (A:B:C = 32.7%: 31.6%: 24.8%) and that of distant metastasis decreased (A:B:C = 9%: 6.1%: 5.3%). Bilateral surgical resection was more commonly used (A:B:C = 62.8%: 89.1%: 94.8%) than lobectomy (A:B:C = 26.3%: 2.8%: 1.8%). Radiation treatment, radioactive iodine (131I; RAI) and external radiotherapy (EXT), was more commonly used (A:B:C = 53.2%: 74.7%: 85.1%). RAI was used in 84.3% (A:B:C = 50%: 71.2%: 84.3%) and EXT in 14.5% of patients in the past decade (A:B:C = 10.9%: 8.7%: 14.5%). The proportion of patients who adopted a bilateral surgery and RAI treatment increased gradually with time (A:B:C = 33%: 68%: 83.8%). The 5-year cause-specific survival (A:B:C = 90.2%: 93.7%: 95.7%), locoregional failure-free survival (A:B:C = 72.6%: 82.9%: 91.6%) and distant metastasis failure-free survival (A:B:C = 84.5%: 89.1%: 92.6%) were improved. However, the period of diagnosis was not found to be an important explanatory variable (i.e. P > 0.05) in Cox regression after adjusting for other factors, indicating that the improvement was probably related to the temporal trend of other factors: presentation at earlier stage, increased ratio of PTC:FTC and more aggressive management by bilateral surgery and radiation therapy.

Follicular thyroid carcinoma: prognostic factors and the role of radioiodine

BACKGROUND

The objective of this study was to investigate the patterns of recurrence, various prognostic factors, and the role of radioiodine in the treatment of patients with follicular thyroid carcinoma (FTC).

METHODS

The clinical outcomes of 215 patients with FTC who were treated at a single institution were analyzed retrospectively. The mean follow-up was 10.8 years.

RESULTS

The actuarial rates of cause specific survival (CSS), locoregional (LR) control, and freedom from distant metastasis (DM) at 10 years were 81%, 83%, and 72.3%, respectively. The independent prognostic factors for survival were metastasis at presentation (relative risk [RR], 47.7), radioiodine (RAI) treatment (RR, 0.25), extrathyroidal extension (RR, 3.8), and the postoperative absence of macroscopic disease in the neck region (RR, 0.06). In patients who were treated with RAI, both the LR failure rate (RR, 0.24) and the mortality rate (RR, 0.25) were reduced to about 25%. Subgroup analysis revealed that RAI improved the survival of patients with DM at presentation (RR, 0.17) and improved the LR control rate in patients who had no DM at presentation (RR, 0.13). For patients who underwent total thyroidectomy with negative resection margins, RAI significantly reduced the rate of LR recurrence (RR, 0.05). Patients with the minimally invasive type of FTC had a good prognosis. The 10-year rates for CSS, LR control, and freedom from DM were 97.6%, 100%, and 90.6%, respectively. The prognosis of patients with frankly invasive FTC was much poorer. The 10-year rates for CSS, LR control, and freedom from DM were 66.7%, 100%, and 45%, respectively.

CONCLUSIONS

RAI is an effective treatment for patients with FTC. It was associated with improved survival rates and fewer recurrences.

Inhibitory effects of calcium channel blockers on thyroid hormone uptake in neonatal rat cardiomyocytes

The effects of the Ca2+ channel blockers verapamil, nifedipine, and diltiazem on triiodothyronine (T3) and thyroxine (T4) uptake were tested in cultured cardiomyocytes from 2-day-old rats. Experiments were performed at 37 degrees C in medium with 0.5% BSA for [125I]T3 (100 pM) or 0.1% BSA for [125I]T4 (350 pM). The 15-min uptake of [125I]T3 was 0.124 +/- 0.013 fmol/pM free T3 (n = 6); [125I]T4 uptake was 0.032 +/- 0.003 fmol/pM free T4 (n = 12). Neither T3 nor T4 uptake was affected by 1% DMSO (diluent for nifedipine and verapamil). Uptake of [125I]T3 but not of [125I]T4 was dose dependently reduced by incubation with 1-100 microM verapamil (49-87%, P < 0.05) or nifedipine (53-81%, P < 0.05). The relative decline in [125I]T3 uptake after 4 h of incubation with 10 microM verapamil or nifedipine was less than after 15 min or 1 h, indicating that the major inhibitory effect of the Ca2+ channel blockers occurred at the level of the plasma membrane. The reduction of nuclear [125I]T3 binding by 10 microM verapamil or nifedipine was proportional to the reduction of cellular [125I]T3 uptake. Diltiazem (1-100 microM) had no dose-dependent effect on [125I]T3 uptake but reduced [125I]T4 uptake by 45% (P < 0.05) at each concentration tested. Neither the presence of 20 mM K+ nor the presence of low Ca2+ in the medium affected [125I]T3 uptake. In conclusion, the inhibitory effects of Ca2+ channel blockers on T3 uptake in cardiomyocytes are not secondary to their effects on Ca2+ influx but, rather, reflect interference with the putative T3 carrier in the plasma membrane.

Cilazapril prevents cardiac hypertrophy and postischemic myocardial dysfunction in hyperthyroid rats

We evaluated the effects of hyperthyroidism on cardiac structural changes and postischemic myocardial function, and also studied how an angiotensin-converting enzyme (ACE) inhibitor, cilazapril, can alter these changes. Hyperthyroidism was induced by daily intraperitoneal injection of thyroxine (T4) (600 microg/kg) with or without cilazapril (10 mg/kg per day, orally), and control rats were given by vehicle. After 2 weeks of treatment, T4-treated rats showed increases in blood pressure and heart weight to body weight ratio (HW:BW). Cilazapril decreased blood pressure to control values and reduced HW:BW. In the isolated working heart preparation, T4-treated rats showed a poor postischemic recovery of left ventricular pressure-rate product (14% of baseline at 30 minutes of reperfusion vs. vehicle 85%) and cardiac work (6% vs. 71%). Cilazapril recovered both values to 49% and 43%. Propranolol (500 mg/L in drinking water) decreased blood pressure to the same extent as cilazapril in hyperthyroid rats, but changed neither HW:BW nor the postischemic myocardial dysfunction. Percent recovery of cardiac work was inversely well correlated with HW:BW (R2 = 0.998, p < 0.001). Results indicate that T4-induced cardiac hypertrophy enhances postischemic cardiac dysfunction. Results also indicate renin-angiotensin system (RAS), but not sympathetic nerve activation, is involved in cardiac hypertrophy and postischemic myocardial dysfunction in hyperthyroid rats.