Thyroid dysfunction and electrocardiographic changes in subjects without arrhythmias: a cross-sectional study of primary healthcare subjects from Copenhagen

Electrocardiographic abnormalities attributable to infiltrative cardiomyopathies: review and prevalence in patients with congestive heart failure

BACKGROUND

The electrocardiogram (ECG) is routinely used in patients with suspected infiltrative cardiomyopathies; heart diseases characterized by the abnormal deposition of pathological substances in the myocardium. This study presents a review of ECG features attributable to various infiltrative cardiomyopathies and analyzes the prevalence and overlap of electrocardiographic abnormalities in patients with adjudicated CHF.

RESULTS

The study included 573 consecutive CHF patients without severe aortic stenosis, further stratified by LV hypertrophy (LVH) and preserved or decreased LV ejection fraction. Comprehensive ECG analysis revealed at least one ECG abnormality typically associated with infiltrative cardiomyopathies in 95% of patients, and more than one ECG abnormality in 70%. An average number of ECG abnormalities was 2.2 ± 1.2 per patient. There was substantial overlap in ECG abnormalities in individual patients, particularly those attributable to Fabry's disease and hemochromatosis (51.5%) or cardiac amyloidosis (46.1%), and hemochromatosis and cardiac amyloidosis (44.2%). Prevalence of various ECG abnormalities was similar across various patient demographics and co-morbidities, including LVH status and/or history of CAD which did not increase the number of ECG abnormalities (2.155 ± 1.238 vs. 2.228 ± 1.192 in patients without CAD history, p = 0.969). Patients with reduced LV ejection fraction had a higher prevalence of widened QRS and premature ventricular complexes.

CONCLUSION

ECG abnormalities attributable to infiltrative cardiomyopathies are common in heart failure patients, with a significant overlap in findings classically attributed to various infiltrative cardiomyopathies. The presence of LVH and decreased LV ejection fraction do not significantly affect the prevalence of ECG abnormalities.

Association between maternal hypothyroidism, baby birth weight, and adult cardiovascular disease risk: insights from ECG measurements

OBJECTIVES

Thyroid hormone (TH) deficiency during pregnancy may affect cardiovascular function in offspring rats. This study aimed to evaluate the effect of TH deficiency during gestation, on the electrocardiogram indices of young and middle-aged offspring of male rats.

METHODS

Eight female rats were equally divided into hypothyroid and control groups. The hypothyroid mothers received 0.025% 6-propyl-2-thiouracil (PTU) in drinking water throughout pregnancy, while control mothers consumed only tap water. Following birth, male rats from each group were observed for 4 months (young age) and 12 months (middle-aged). The group known as fetal hypothyroid (FH) consisted of rats born from hypothyroid mothers. The serum T4 and TSH concentrations from mothers and newborn male rats were assayed at the end of gestation. Lead II electrocardiogram (ECG) was recorded for 5 minutes using Power Lab, AD Instruments.

RESULTS

There was a significant rise in the P wave voltage in young FH rats, whereas, it was decreased in middle-aged control and FH rats. The voltage of QRS decreased and its duration increased in the young and middle-aged FH rats compared to the corresponding control groups. Duration and voltage of the T wave were significantly altered in the young and middle-aged FH groups. PR and QT intervals significantly increased in the young and middle-aged FH groups compared to their controls.

CONCLUSIONS

Maternal hypothyroidism affected the electrocardiogram indices of offspring rats, possibly signaling cardiovascular problems later in life.

Hypothyroidism Presenting Atypically as an Isolated Pericardial and Pleural Effusion: A Case Report

Hypothyroidism is an endocrine disorder characterized by low thyroid hormone levels, which commonly presents as fatigue, cold intolerance, constipation, poor memory and/or concentration, and weight gain. Common signs of hypothyroidism include bradycardia, electrocardiograph changes, a lower basal temperature, a slower relaxation phase of deep tendon reflexes, and swelling of the extremities. Hypothyroidism is diagnosed with labs showing high thyroid-stimulating hormone levels and low free thyroxine. Hypothyroidism may present as a pericardial or pleural effusion, with the incidence of each being unknown. The paucity of information regarding the incidence of pericardial and pleural effusions in hypothyroidism may be due to effusions being an atypical complication of a common endocrine disorder. Hypothyroidism, including in cases of pericardial or pleural effusions, is typically treated with thyroid hormone replacement therapy, usually in the form of levothyroxine. Hemodynamic compromise may necessitate pericardiocentesis or pleurocentesis. In this case report, we present an atypical presentation of hypothyroidism that is characterized by an isolated pericardial and pleural effusion in a patient with post-thyroidectomy hypothyroidism who was non-adherent to levothyroxine. We discuss the pathophysiology of pleural and pericardial effusions in thyroid disease, which is thought to involve increased capillary permeability and changes in oncotic pressure related to albumin. We also review treatment strategies regarding pericardial and pleural effusions in hypothyroidism.

Artificial intelligence-enabled electrocardiography contributes to hyperthyroidism detection and outcome prediction

BACKGROUND

Hyperthyroidism is frequently under-recognized and leads to heart failure and mortality. Timely identification of high-risk patients is a prerequisite to effective antithyroid therapy. Since the heart is very sensitive to hyperthyroidism and its electrical signature can be demonstrated by electrocardiography, we developed an artificial intelligence model to detect hyperthyroidism by electrocardiography and examined its potential for outcome prediction.

METHODS

The deep learning model was trained using a large dataset of 47,245 electrocardiograms from 33,246 patients at an academic medical center. Patients were included if electrocardiograms and measurements of serum thyroid-stimulating hormone were available that had been obtained within a three day period. Serum thyroid-stimulating hormone and free thyroxine were used to define overt and subclinical hyperthyroidism. We tested the model internally using 14,420 patients and externally using two additional test sets comprising 11,498 and 596 patients, respectively.

RESULTS

The performance of the deep learning model achieves areas under the receiver operating characteristic curves (AUCs) of 0.725-0.761 for hyperthyroidism detection, AUCs of 0.867-0.876 for overt hyperthyroidism, and AUC of 0.631-0.701 for subclinical hyperthyroidism, superior to a traditional features-based machine learning model. Patients identified as hyperthyroidism-positive by the deep learning model have a significantly higher risk (1.97-2.94 fold) of all-cause mortality and new-onset heart failure compared to hyperthyroidism-negative patients. This cardiovascular disease stratification is particularly pronounced in subclinical hyperthyroidism, surpassing that observed in overt hyperthyroidism.

CONCLUSIONS

An innovative algorithm effectively identifies overt and subclinical hyperthyroidism and contributes to cardiovascular risk assessment.

A Prospective Observational Study to Evaluate Cardiovascular Changes in Patients of Hypothyroidism

Introduction Hypothyroidism is a common endocrine disorder in India and is easy to diagnose based on clinical manifestations and signs. Thyroid hormone affects the cardiovascular system. Fatiguability, dyspnea, weight gain, lower limb swelling, and bradycardia are some clinical manifestations. ECG changes in hypothyroidism include sinus bradycardia, prolonged QTc interval, changes in the morphology of the T-wave, QRS duration, and low voltage. Echocardiography changes include diastolic dysfunction, asymmetrical septal hypertrophy, and pericardial effusion. This study aimed to examine the cardiovascular changes in patients with hypothyroidism. Methodology Patients with hypothyroidism and cardiovascular changes were assessed using an electrocardiogram and echocardiography. Results A total of 68 hypothyroid patients were enrolled in the study. The mean age of patients was 41.93 ± 15.36 years, and the mean BMI was 24.64 ± 4.30 kg/m². Of 68 hypothyroid patients, 57 (83.8%) were females, and 11 (16.2%) were males. The mean thyroid-stimulating hormone (TSH) level in the study population was 11.48 ± 22.02 (mIU/mL). The most common symptoms reported among the study participants were tiredness or weakness (67.6%), followed by dyspnea (42.6%). The mean pulse rate, systolic blood pressure, and diastolic blood pressure were 81.50 ± 16.16, 112.76 ± 7.05, and 70.68 ± 7.46, respectively. Pallor was the most common sign (22.1%) among all the people who participated in the study. The most common findings on the ECG were low voltage complexes (25%) followed by inversion of the T wave (23.5%). Other ECG findings were bradycardia (10.3%), right bundle branch block (7.4%), and QRS prolongation (2.9%). Echocardiography revealed 21 (30.8%) patients with grade 1 left ventricular diastolic dysfunction and pericardial effusion in two patients (2.94%). There was a significantly greater increase in the level of TSH in study participants. Conclusion Patients with abnormal ECG and echocardiography without other cardiovascular changes should be evaluated for hypothyroidism to improve the quality of care.

Assessment of Electrocardiographic Changes and Associated Factors Among Thyroid Dysfunction Patients Attending Jimma Medical Center, Southwest Ethiopia: A Cross-Sectional Study

Background

Thyroid dysfunction (TD) is a metabolic manifestation related to either excessive or inadequate production of thyroid hormones. It has been widely proven to have comorbidities like cardiovascular disease. An electrocardiograph is a simple investigative instrument used to assess cardiac status to prevent complications in the later stages of the disease.

Objective

To assess electrocardiogram (ECG) changes and associated factors among TD patients.

Methods

An institution-based cross-sectional study was conducted among 273 TD patients attending Jimma Medical Center from October 11 to December 11, 2021. An ECG tool with 12 leads was used to assess the cardiac status, and a semi-structured questionnaire was used to assess sociodemographic, behavioral, and comorbidity variables. Bodyweight, height, waist circumference (WC), hip circumference (HC), and blood pressure variables were recorded, and body mass index (BMI) and waist-to-hip ratio (WHR) were calculated.

Results

Out of a total of 273 analyzed and interpreted ECG results by the cardiologists, 185 (67.8%) had ECG alterations. The most common types of ECG changes were arrhythmia 153 (56%), followed by myocardial infarction 74 (27.1%), ventricular hypertrophy [left 20 (7.3%) and right 15 (5.5%)], left atrial enlargement 3 (1%), axis deviation, and other abnormalities 24 (8.8%) and 18 (6.6%), respectively. The identified predictor variables for the ECG changes were the age group of 41 to 60 years old [AOR = 2.5, 95% CI: 1.25, 5.05], being female [AOR = 2.7, 95% CI: 1.28, 5.59], having diabetes mellitus [AOR = 4.25, 95% CI: 1.6, 11.2], and not starting the treatment [AOR = 8.6, 95% CI: 3.45, 21.6].

Conclusion

This study revealed that the prevalence of ECG changes was high among TD patients. The most common type of ECG change observed was arrhythmia followed by myocardial infarction. The age range of 41-60 years old, being female, having diabetes mellitus, and not starting the treatment were significantly associated with the ECG changes. Implementing an efficient noninvasive screening of cardiac status can detect unrecognized and asymptomatic cardiac impairment in TD patients.

The bidirectional relationship of thyroid disease and atrial fibrillation: Established knowledge and future considerations

Atrial fibrillation (AF) tends to occur frequently in patients with thyroid disease, primarily hyperthyroidism. In hyperthyroidism, increased levels of thyroid hormones, via intra- and extranuclear mechanisms, have profound effects on cardiac electrophysiology. Hypothyroidism carries a lower risk for AF and is mainly associated with the overtreatment of hypothyroid patients. New-onset AF is frequently the only manifestation of thyroid disease, which renders screening for thyroid dysfunction in that scenario clinically useful. Managing thyroid disease and comorbid AF is essential. This includes thyroid hormones control along with conventional AF therapy. However, there are several open issues with this comorbid duo. The optimal management of thyroid disease and its impact on AF burden remains obscure. There is scanty information on clear-cut benefits for therapy of subclinical thyroid disease and screening of asymptomatic patients. Furthermore, the immunogenetic overlap between the autoantibodies in Graves' disease and AF genesis may lead to novel therapeutic implications. The objective of this review is to summarize the up-to-date epidemiology, pathogenesis, pathophysiology and management of interacting thyroid disease and AF.

Electrocardiographic biomarker based on machine learning for detecting overt hyperthyroidism

Aims

Although overt hyperthyroidism adversely affects a patient's prognosis, thyroid function tests (TFTs) are not routinely conducted. Furthermore, vague symptoms of hyperthyroidism often lead to hyperthyroidism being overlooked. An electrocardiogram (ECG) is a commonly used screening test, and the association between thyroid function and ECG is well known. However, it is difficult for clinicians to detect hyperthyroidism through subtle ECG changes. For early detection of hyperthyroidism, we aimed to develop and validate an electrocardiographic biomarker based on a deep learning model (DLM) for detecting hyperthyroidism.

Methods and results

This multicentre retrospective cohort study included patients who underwent ECG and TFTs within 24 h. For model development and internal validation, we obtained 174 331 ECGs from 113 194 patients. We extracted 48 648 ECGs from 33 478 patients from another hospital for external validation. Using 500 Hz raw ECG, we developed a DLM with 12-lead, 6-lead (limb leads, precordial leads), and single-lead (lead I) ECGs to detect overt hyperthyroidism. We calculated the model's performance on the internal and external validation sets using the area under the receiver operating characteristic curve (AUC). The AUC of the DLM using a 12-lead ECG was 0.926 (0.913-0.94) for internal validation and 0.883(0.855-0.911) for external validation. The AUC of DLMs using six and a single-lead were in the range of 0.889-0.906 for internal validation and 0.847-0.882 for external validation.

Conclusion

We developed a DLM using ECG for non-invasive screening of overt hyperthyroidism. We expect this model to contribute to the early diagnosis of diseases and improve patient prognosis.

Thyroid hormones regulate cardiac repolarization and QT-interval related gene expression in hiPSC cardiomyocytes

Prolongation of cardiac repolarization (QT interval) represents a dangerous and potentially life-threatening electrical event affecting the heart. Thyroid hormones (THs) are critical for cardiac development and heart function. However, little is known about THs influence on ventricular repolarization and controversial effects on QT prolongation are reported. Human iPSC-derived cardiomyocytes (hiPSC-CMs) and multielectrode array (MEA) systems were used to investigate the influence of 3,3',5-triiodo-L-Thyronine (T3) and 3,3',5,5'-tetraiodo-L-Thyronine (T4) on corrected Field Potential Duration (FPDc), the in vitro analog of QT interval, and on local extracellular Action Potential Duration (APD). Treatment with high THs doses induces a significant prolongation of both FPDc and APD, with the strongest increase reached after 24 h exposure. Preincubation with reverse T3 (rT3), a specific antagonist for nuclear TH receptor binding, significantly reduces T3 effects on FPDc, suggesting a TRs-mediated transcriptional mechanism. RNA-seq analysis showed significant deregulation in genes involved in cardiac repolarization pathways, including several QT-interval related genes. In conclusion, long-time administration of high THs doses induces FPDc prolongation in hiPSC-CMs probably through the modulation of genes linked to QT-interval regulation. These results open the way to investigate new potential diagnostic biomarkers and specific targeted therapies for cardiac repolarization dysfunctions.

Association of thyroid-stimulating hormone with corrected QT interval variation: A prospective cohort study among patients with type 2 diabetes

BACKGROUND

Patients with type 2 diabetes mellitus (T2DM) have a prolonged QT interval and are at high risk of sudden cardiac death. A prolonged QT interval, indicative of impaired ventricular repolarization, is a risk factor for lethal ventricular arrhythmias, such as torsades-de-pointes (TdP).

AIMS

To identify key clinical and biochemical covariates associated with Fridericia's corrected QT interval (QTcF) among euthyroid patients with T2DM, and to describe the temporal relationship between these factors and QTcF.

METHODS

We performed prospective, clinical, biochemical and electrocardiographic measurements among patients with T2DM enrolled in the DIACART study at Pitié-Salpêtrière Hospital, at T1 (baseline) and T2 (follow-up), with a median interval of 2.55 years.

RESULTS

Mean age (63.9±8.5 years), sex (22.35% women), drugs with known risk of TdP according to the CredibleMeds website (Cred-drugsTdP) and serum thyroid-stimulating hormone (TSH) concentrations correlated with QTcF in univariate analysis at both T1 and T2. In multivariable analysis, all these covariates except age were significantly associated with QTcF at both T1 (women: standardized β=0.24±0.07, P=0.001; Cred-drugsTdP: β=0.19±0.07, P=0.007; TSH concentration: β=0.18±0.07, P=0.01) and T2 (women: β=0.25±0.08, P=0.002; Cred-drugsTdP: β=0.25±0.08, P=0.001; TSH concentration: β=0.19±0.08, P=0.01). Furthermore, variation in QTcF over the years was associated with variation in TSH concentration (r=0.24, P=0.007) and changes in use of Cred-drugsTdP (r=0.2, P=0.02).

CONCLUSIONS

Serum TSH concentration and its variation were associated with QTcF and its variation, even after correcting for the main determinants of QTcF. Interventional optimization of TSH concentration in T2DM warrants further investigation to establish its impact on the risk of TdP and sudden cardiac death.

Prediction of biological age and all-cause mortality by 12-lead electrocardiogram in patients without structural heart disease

Background

There is a well-established relationship between 12-lead electrocardiogram (ECG) and age and mortality. Furthermore, there is increasing evidence that ECG can be used to predict biological age. However, the utility of biological age from ECG for predicting mortality remains unclear.

Methods

This was a single-center cohort study from a cardiology specialized hospital. A total of 19,170 patients registered in this study from February 2010 to March 2018. ECG was analyzed in a final 12,837 patients after excluding those with structural heart disease or with pacing beats, atrial or ventricular tachyarrhythmia, or an indeterminate axis (R axis > 180°) on index ECG. The models for biological age were developed by principal component analysis (BA) and the Klemera and Doubal’s method (not adjusted for age [BA_E] and adjusted for age [BA_EC]) using 438 ECG parameters. The predictive capability for all-cause death and cardiovascular death by chronological age (CA) and biological age using the three algorithms were evaluated by receiver operating characteristic analysis.

Results

During the mean follow-up period of 320.4 days, there were 55 all-cause deaths and 23 cardiovascular deaths. The predictive capabilities for all-cause death by BA, BA_E, and BA_EC using area under the curves were 0.731, 0.657, and 0.685, respectively, which were comparable to 0.725 for CA (p = 0.760, 0.141, and 0.308, respectively). The predictive capabilities for cardiovascular death by BA, BA_E, and BA_EC were 0.682, 0.685, and 0.692, respectively, which were also comparable to 0.674 for CA (p = 0.775, 0.839, and 0.706, respectively). In patients aged 60–74 years old, the area under the curves for all-cause death by BA, BA_E, and BA_EC were 0.619, 0.702, and 0.697, respectively, which tended to be or were significantly higher than 0.482 for CA (p = 0.064, 0.006, and 0.005, respectively).

Conclusion

Biological age by 12-lead ECG showed a similar predictive capability for mortality compared to CA among total patients, but partially showed a significant increase in predictive capability among patients aged 60–74 years old.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-021-02391-8.

Challenges in the Management of Atrial Fibrillation With Subclinical Hyperthyroidism

Subclinical thyroid disorders have a high prevalence among older individuals and women. Subclinical hypothyroidism is diagnosed by elevated serum levels of thyroid-stimulating hormone (TSH) with thyroxine levels within the reference range, and subclinical hyperthyroidism is diagnosed by low TSH in conjunction with thyroxine and triiodothyronine levels within reference ranges. Atrial fibrillation is the most commonly diagnosed cardiac arrhythmia and has been associated with an increased risk of mortality, heart failure, stroke, and depression. Mechanistic data from animal and human physiology studies as well as observational data in humans support an association of subclinical hyperthyroidism with atrial fibrillation. Guidelines recommend the measurement of TSH in the evaluation of new-onset atrial fibrillation. All patients with overt hyperthyroidism should be treated, and treatment of subclinical hyperthyroidism should be considered in patients older than 65 years with TSH < 0.4 mlU/L, or in younger patients with TSH < 0.1 mlU/L. Guidelines also recommend screening for AF in patients with known hyperthyroidism. Wearable devices that measure the heart electrical activity continuously may be a novel strategy to detect atrial fibrillation in patients at risk. In this review, we explore the interplay between thyroid hormones and atrial fibrillation, management controversies in subclinical hyperthyroidism, and potential strategies to improve the management of atrial fibrillation in patients with subclinical hyperthyroidism.

Assessment of Hypertension Using Clinical Electrocardiogram Features: A First-Ever Review

Hypertension affects an estimated 1.4 billion people and is a major cause of morbidity and mortality worldwide. Early diagnosis and intervention can potentially decrease cardiovascular events later in life. However, blood pressure (BP) measurements take time and require training for health care professionals. The measurements are also inconvenient for patients to access, numerous daily variables affect BP values, and only a few BP readings can be collected per session. This leads to an unmet need for an accurate, 24-h continuous, and portable BP measurement system. Electrocardiograms (ECGs) have been considered as an alternative way to measure BP and may meet this need. This review summarizes the literature published from January 1, 2010, to January 1, 2020, on the use of only ECG wave morphology to monitor BP or identify hypertension. From 35 articles analyzed (9 of those with no listed comorbidities and confounders), the P wave, QTc intervals and TpTe intervals may be promising for this purpose. Unfortunately, with the limited number of articles and the variety of participant populations, we are unable to make conclusions about the effectiveness of ECG-only BP monitoring. We provide 13 recommendations for future ECG-only BP monitoring studies and highlight the limited findings in pregnant and pediatric populations. With the advent of convenient and portable ECG signal recording in smart devices and wearables such as watches, understanding how to apply ECG-only findings to identify hypertension early is crucial to improving health outcomes worldwide.

New-onset arrhythmia associated with patients hospitalized for thyroid dysfunction

BACKGROUND

Thyroid dysfunction has been associated with cardiovascular dysfunction in the literature. However, the frequency of new-onset arrhythmias associated with thyroid disease hospitalization is unknown. Hence, we analyzed frequency, in-hospital outcomes, and resource utilization of new-onset arrhythmias associated with thyroid dysfunction hospitalizations.

METHODS

The patients who were admitted with the primary reason of thyroid dysfunction were included using appropriate international classification of disease, ninth revision, clinical modification (ICD-9-CM) codes. We then identified new-onset arrhythmias using appropriate ICD-9-CM codes. We utilized the "present on admission" variable to exclude arrhythmias that were present on admission.

RESULTS

Among the eligible patients with thyroid dysfunction, only 3% (n=12,111) developed a new-onset arrhythmia. Atrioventricular block (1.49%) is the most frequent followed by atrial fibrillation (0.92%), ventricular tachycardia (0.47%), atrial flutter (0.23%), supraventricular tachycardia (0.1%) and ventricular fibrillation (0.07%). Patients with new-onset arrhythmias were older (mean age 76.7±12.5 years), more predominantly white (n=9008, 74.4%), higher females (n= 7632, 63%), and had a higher frequency of comorbidities. In-hospital mortality occurred in 827 (6.8%) patients with new-onset arrhythmias and 8632 (2.2%) patients without new-onset arrhythmias (P-value <0.001). The medical length of stay and cost of hospitalization was also higher in these patients.

CONCLUSION

Thyroid dysfunction is not associated with significantly higher rates of new-onset arrhythmias while inpatient. However, when developed, these arrhythmias are associated with higher mortality and resource utilization. The patients admitted to the hospital should have thyroid function checked when found to have an arrhythmia.

Early L-T4 intervention improves fetal heart development in pregnant rats with subclinical hypothyroidism rats by activating BMP4/Smad4 signaling pathway

BACKGROUND

It is unclear whether the offspring of subclinical hypothyroidism (SCH) pregnant rats still have abnormal cardiac development, and whether early intervention with L-T4 can improve the abnormality of these offspring. Therefore, the aim of this study was to investigate the effect of early L-T4 intervention on the heart development of offspring of SCH pregnant rats and its possible molecular mechanism.

METHODS

Eighty female Wistar rats were randomly divided into Sham group (placebo control), SCH group, LT4-E10 group (L-T4 treatment started on the 10th day of gestation), and LT4-E13 group (L-T4 treatment started on the 13th day of gestation). Each group was further divided into E16 (16th day of gestation), E18 (18th day of gestation), P5 (5th day postnatal day), and P10 (10th day postnatal day) subgroups. The levels of serum TT4 and TSH, the ratio of heart weight to body weight of offspring rats, the expression of metabolic enzymes, and the histopathology of cardiomyocytes were determined. To elucidate the effects of L-T4 on cardiac development of offspring of SCH pregnant rats, the expression levels of GATA4, Nkx2-5 and proteins involved in BMP4/Smad4 signaling pathway were detected by immunohistochemistry, real time quantitative polymerase chain reaction and Western blotting to elucidate the molecular mechanism of L-T4 regulating the heart development of the offspring of SCH pregnant rats.

RESULTS

Compared with Sham group, serum TSH was significantly increased in SCH pregnant rats. Moreover, early L-T4 intervention significantly reduced the levels of serum TSH. Compared with the offspring in the SCH group, early L-T4 intervention significantly increased the heart weight, heart weight to body weight ratio, the activities of succinate dehydrogenase (SDH), Na⁺/K⁺-ATPase and Ca²⁺-ATPase, but reduced myocardial cell shrinkage and nuclear staining, hyperemia/congestion and vacuolar degeneration. In addition, early L-T4 intervention not only significantly increased the mRNA and protein expression of Gata4 and Nkx2-5, but also increased the protein expression involved in BMP4/Smad4 signal pathway in myocardium of the offspring of SCH pregnant rats.

CONCLUSIONS

Early L-T4 intervention can regulate the cardiac development of the offspring of SCH pregnant rats by activating BMP4/Smad4 signaling pathway and increasing the expression of Gata4 and Nkx2-5 proteins.

Electrocardiography in euthyroid individuals: a Danish general population study

BACKGROUND

Thyroid hormones within the euthyroid range have been linked to mortality and differences in heart rate. However, some relations between thyroid hormone concentration and various electrocardiographic measurements remain unassessed. We aimed to investigate the association between thyroid hormone concentrations within the euthyroid range and different electrocardiographic markers in people free of thyroid disease.

METHODS

We obtained electrocardiograms (ECG) and blood samples of free T4, total T3, and thyrotropin (TSH) in 20,852 subjects from the general population (the GESUS study). Relations between concentrations of TSH, free T4, and total T3 and heart rate, QTc, QRS duration, PR interval, P-wave duration and T-wave morphology were assessed in a multivariate adjusted linear model stratified by sex.

RESULTS

Roughly half of the 18,046 included participants with thyroid hormone measurements within euthyroid range were men, and the average age was 56 years. Heart rate increased with concentrations of T3 (6.4 bpm/nM, P<0.001 in women and 5.3 bpm/nM, P<0.001 in men) and T4 (3.7 bpm/10pM, P<0.001 in women and 3.1 bpm/10pM, P<0.001 in men). We found no relation between TSH and heart rate. PR interval and QRS duration decreased with higher concentrations of T3 (all P<0.01). QTc increased with higher concentrations of T4 in men (5 ms/10pM), and T waves were flatter, more asymmetric, and more often had notches with higher concentrations of T4 (all P≤0.01).

CONCLUSIONS

Thyroid hormone concentrations within the euthyroid range in people free of thyroid disease were associated with changes in the electrocardiogram in a general population.