Hypothyroidism, thyroxine treatment, and the heart

Hypothyroidism complicates bradyarrhythmic episodes in a heart-transplanted patient: Can it be treated with low-dose dopamine?

Extracorporeal circulation decreases thyroid hormone levels in peripheral blood. This clinical entity may complicate the postoperative period after heart transplantation if the recipient has taken thyroid hormone replacement therapy. Cardiac transplantation was performed on a patient in whom thyroid hormone levels decreased after surgery. Sinus bradycardia was seen after surgery (30-40 bpm). Thyroid hormones were replaced in the patient. Due to the fact that temporary pacing decreased blood pressure, dopamine was safely given in very low doses. This case was discussed under the literature knowledge.

Co-administration of Apelin and T4 protects inotropic and chronotropic changes occurring in hypothyroid rats

BACKGROUND

One of the most important thyroid hormone targets is the cardiovascular system. Hemodynamic changes, such as decreased resting heart rate (HR), myocardial contractility, and cardiac output, and increased diastolic pressure and systemic vascular resistance, have been observed in hypothyroid patients. Moreover, in these patients, ECG changes include sinus bradycardia and low voltage complexes (P waves or QRS complexes).

OBJECTIVE

This study aimed at evaluating the prophylactic effect of apelin on HR changes and QRS voltage that occur in propylthiouracil (PTU)-induced hypothyroid rats.

METHOD

In this study, 48 adult male Wistar rats weighing 170-235g were randomly divided into 6 groups: Control group (normal saline ip injection + tap water gavage); P group (PTU 0.05%, in drinking water); A group (apelin 200 µg.kg-1.day-1, ip); PA group [co-administration of PTU and apelin]; PT group [co-administration of PTU + T4 (0.2 mg/g per day, gavage)]; and PAT group (co-administration of PTU, apelin and T4). All experiments were performed for 28 consecutive days, and then the animals were anesthetized with an ip injection of ketamine (80 mg/kg) and xylazine (12 mg/kg). Lead II electrocardiogram was recorded to calculate HR and QRS voltage.

RESULTS

Heart rate and QRS voltage increased more significantly in the hypothyroid group that consumed both apelin and T4 (201 ± 4 beat/min, 0.71 ± 0.02 mv vs. hypothyroid 145 ± 9 beat/min, 0.563 ± 0.015 mv; respectively).

CONCLUSION

The co-administration of apelin and T4 showed a protective effect on QRS voltage and HR in PTU‑induced hypothyroid rats.

A case of hypothyroidism mimicking acute coronary syndrome

Hypothyroid patients have increased concentrations of creatinine kinase that is mostly due to increased CK-MM. However, CK-MB has also been reported to increase above reference values in hypothyroid patients without apparent myocardial damage. This may create confusion during the evaluation of myocardial injury in a hypothyroid patient presenting with chest pain. Troponin I is considered as a superior marker for the diagnosis of myocardial infarction in hypothyroid patients. However, there are some reports showing an increase in the level of troponin I without any myocardial damage in hypothyroid patients as in our case. In this report, we present a 47 years old male hypothyroid patient who had chest pain, abnormal electrocardiographic findings and increased cardiac enzymes suggesting acute coronary syndrome although he had normal coronary arteriogram.

[Hypothyroid dilated cardiomyopathy]

Most patients with dilated cardiomyopathy have a poor prognosis due to progressive and irreversible myocardial dysfunction. Rarely, is a metabolic etiology responsive to specific therapy identified. Although many studies have confirmed that thyroid hormone deficiency is associated with a reversible decrease in myocardial contractility, it has remained controversial whether hypothyroidism alone can cause a dilated cardiomyopathy and clinical heart failure. In this study, we report the case of a patient with severe hypothyroidism and a dilated cardiomyopathy complicated by heart failure, which has receded after recovery to euthyroidism with L-thyroxin therapy. This case suggests that hypothyroidism should be evoked systematically when a dilated cardiomyopathy is diagnosed.

Thalidomide-induced sinus bradycardia

OBJECTIVE

To report a case of thalidomide-induced sinus bradycardia in an elderly man.

CASE SUMMARY

A 72-year-old white man, with transfusion-dependent refractory anemia with ringed sideroblasts and hypertension treated with atenolol, was started on thalidomide 100 mg at bedtime. During the dose titration period (maximum dose 400 mg/d), his heart rate decreased from a baseline of 63 beats/min to as low as 44 beats/min with positive electrocardiogram findings of sinus bradycardia. After discontinuation of atenolol, the patient's heart rate increased to 68 beats/min, but symptoms of bradycardia persisted. Due to the patient's continued dizziness and lightheadedness, thalidomide was discontinued. In the 3 months following discontinuation of thalidomide, the patient's heart rate increased to an average of 74 beats/min.

DISCUSSION

Clinical trials and postmarketing surveillance suggest that the incidence of thalidomide-induced bradycardia is low. The mechanism of this effect is unknown. Concurrent medications affecting the heart rate may also increase the risk of thalidomide-induced bradycardia. Following titration of thalidomide to a maximum dose of 400 mg/d, our patient's heart rate decreased markedly, resulting in intermittent symptoms of lightheadedness and dizziness. He may have been at higher risk of thalidomide-induced bradycardia because of concurrent administration of atenolol. An objective causality assessment revealed that the adverse event was probable.

CONCLUSIONS

Despite the low incidence of thalidomide-induced bradycardia, it appears to be an important adverse effect, particularly in patients with comorbidities or concurrent medications that decrease heart rate. Therefore, providers should monitor these patients closely for signs and symptoms of bradycardia during the administration of thalidomide.

Epidemiology and prevention of clinical and subclinical hypothyroidism

Iodine deficiency is the most common cause of hypothyroidism worldwide. In persons living in iodine-replete areas, causes are congenital, spontaneous because of chronic autoimmune disease (atrophic autoimmune thyroiditis or goitrous autoimmune thyroiditis [Hashimoto's thyroiditis]), or iatrogenic because of goitrogens, drugs, or destructive treatment for thyrotoxicosis. Screening for congenital hypothyroidism exists and its use prevents mental retardation. The prevalence of spontaneous hypothyroidism is between 1% and 2% and is more common in older women and 10 times more common in women than in men. A significant proportion of subjects have asymptomatic chronic autoimmune thyroiditis and 8% of women (10% of women over 55 years of age) and 3% of men have subclinical hypothyroidism. Approximately one third of patients with newly diagnosed overt hypothyroidism have received destructive therapy for hyperthyroidism and indefinite surveillance is required. There is not much that can be done to prevent the occurrence of spontaneous autoimmune hypothyroidism, but if identified early, something can be done to prevent progression to overt disease. Controversy exists as to whether healthy adults would benefit from screening for autoimmune thyroid disease because a significant proportion of subjects tested will have evidence of mild thyroid failure. Case finding in women at menopause or visiting a primary care physician with nonspecific symptoms appears justified.

Population screening for autoimmune thyroid disease

Whether or not healthy adults in the community would benefit from screening for autoimmune thyroid disease is controversial. Although the prevalence of unsuspected overt thyroid disease is low, a significant proportion of subjects tested will have evidence of mild thyroid failure or excess. This article assesses whether subclinical thyroid disease is of sufficient clinical importance to warrant screening and, once detected and confirmed, to justify therapy. Population screening for autoimmune thyroid disease is assessed against recently revised screening criteria, using data from epidemiologic studies. Recommendations are proposed that may be applied in any iodine-replete community.

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.