Effect of thyrotropin suppressive therapy on heart rate variability and QT dispersion in patients with differentiated thyroid cancer

Silent Signals: Analyzing Repolarization Heterogeneity and Autonomic Modulation in Children With Euthyroid Hashimoto's Thyroiditis

BACKGROUND

Hashimoto's thyroiditis is the most prevalent autoimmune thyroid condition in children, typically appearing in a euthyroid state. The cardiovascular impact of euthyroid Hashimoto's thyroiditis (eHT) remains poorly understood, especially regarding its connection to arrhythmias and autonomic dysfunction. This study aimed to evaluate electrocardiographic markers of repolarization inhomogeneity (P-wave dispersion (Pd), QT dispersion (QTd), and peak-to-end interval of the T-wave (Tp-e)) as well as heart rate variability (HRV) in children with eHT to assess the asymptomatic cardiovascular effects that may predispose them to future arrhythmias.

MATERIALS AND METHODS

This retrospective analysis involved 67 patients and 50 healthy controls. Patients were evaluated for anthropometric and biochemical parameters, electrocardiogram (ECG) results, echocardiographic findings, and 24-hour Holter monitoring. ECG parameters were measured and analyzed for repolarization indices, while HRV was assessed using time-domain and frequency-domain analyses.

RESULTS

Patients exhibited significantly longer P max, Pd, QT intervals, QTd, and Tp-e intervals than the controls (all p < 0.001). A receiver operating characteristic analysis indicated that a Pd of 51 ms predicted the disease with 67% sensitivity and 72% specificity (area under the curve: 0.733, p = 0.001, 95% CI: 0.643-0.823). Time-domain HRV parameters (SD of all normal-to-normal intervals and SD of all the five-minute normal-to-normal intervals) were significantly lower in eHT patients, indicating an autonomic imbalance. At the same time, frequency-domain analyses revealed no significant differences.

CONCLUSIONS

Children with eHT exhibit increased myocardial repolarization heterogeneity and reduced HRV, indicating a potential risk for arrhythmias. These findings highlight the necessity of regular cardiac symptom inquiry and ECG controls in the follow-up of these patients, considering both thyroid function and underlying autoimmune processes. Further research is needed to clarify the long-term cardiovascular risks of eHT in children.

Do Different TSH Suppression Levels Effect Heart Rate Variability and QT Dispersions in Patients with Differentiated Thyroid Cancer?

OBJECTIVE

The aim of this study was to investigate changes in heart rate variability (HRV) and QT dispersion (QTd) in patients with differentiated thyroid cancer at different TSH suppression levels.

METHODS

The study included 125 DTC patients, who had been on TSH suppression treatment (TSHST) for at least 1 year. The patients were categorized into three groups: patients with TSH < 0.1 mIU/L (n:30), those with TSH 0.1 to 0.5 mIU/L (n:56), and those with TSH 0.5 to 2 mIU/L (n:39). The first two groups were classified as suppression groups, and the last as replacement (control) group. All patients underwent 12-lead electrocardiogram (ECG) recording and 24-hour rhythm holter echocardiography analysis.

RESULTS

The HRV results derived from a 24-hour rhythm holter did not exhibit any significant difference (p < 0.05). In dispersion evaluations, the QTd was significantly longer in the suppression groups (groups 1 and 2), than in the replacement group (group 3) (p < 0.001 and p:0.002, respectively). The same was found for corrected QT dispersion (QTcd) (p < 0.001 and p: 0.008, respectively). In multivariate linear regression analysis, TSH was found to affect QTd (β = -0.299; p = 0.002) and QTcd (β = -0.300; p = 0.002) values independently.

CONCLUSION

In this study, it was shown that in patients with DTC receiving TSHST, QT dispersion prolonged as the TSH suppression level increased. Especially in high-risk DTC patients, evaluation of QTd may be useful in terms of evaluating cardiovascular risk and regulating TSHST level.

Association between thyroid cancer and cardiovascular disease risk: a nationwide observation study

Treatment with levothyroxine and radioiodine contribute alternative cardiovascular function in adults with thyroid cancer. The risks of long-term cardiovascular conditions among thyroid cancer patients is unknown. This study aimed to compare the incidence of coronary heart disease (CHD), ischemic stroke (IS), and atrial fibrillation (AF) among adults with thyroid cancer with that of the general population, especially when stratified by age (< 65 and ≥ 65 years old). This observational cohort study enrolled patients between January 1, 2011 and December 31, 2016 with a follow-up until December 31, 2018. This study analyzed the data of Taiwanese thyroid cancer patients registered on the National Taiwan Cancer Registry Database, with CHD and IS. SIR models were used to evaluate the association between thyroid cancer and CHD, IS, AF, and cardiovascular disease outcome, stratified by age and sex. SIR analyses were also conducted for both sexes, age groups (< 65, ≥ 65 years), and different follow-up years. After excluding 128 individuals (< 20 years or ≥ 85 years old) and with missing index data, 4274 eligible thyroid cancer patients without CHD history, 4343 patients without IS history, and 4247 patients without AF history were included for analysis. During the median follow-up of 3.5 (1.2) years among thyroid cancer patients, the observed number of new CHD events was 70; IS, 30; and AF, 20, respectively. The SIR was significantly higher for CHD (SIR, 1.57; 95% confidence interval [CI] 1.2-1.93) among thyroid cancer patients compared with the age- and sex-specific standardized population. However, the association between thyroid cancer and the risks of IS (SIR, 0.74; 95% CI 0.47-1), cardiovascular disease (SIR, 0.88; 95% CI 0.7-1.05), and atrial fibrillation (SIR, 0.74; 95% CI 0.42-1.06) were insignificant. Moreover, stratification by age < 65 or age ≥ 65 years old and by sex for CHD suggested that the diagnosis of thyroid cancer in the young may attenuate the CHD risk (SIR, 2.08; 95% CI 1.5-2.66), and the CVD risk was constant among both men (SIR, 1.63; 95% CI 1.03-2.24) and women (SIR, 1.53; 95% CI 1.06-1.99). The patients had persistent higher CHD risk for 5 years after cancer diagnosis. Thyroid cancer survivors have a substantial CHD risk, even at long-term follow-up, especially in those patients < 65 years old. Further research on the association between thyroid cancer and CHD risk is warranted.

Abnormal Cardiac Repolarization in Thyroid Diseases: Results of an Observational Study

Background: The relationship between thyroid function and cardiac disease is complex. Both hypothyroidism and thyrotoxicosis can predispose to ventricular arrhythmia and other major adverse cardiovascular events (MACE), so that a U-shaped relationship between thyroid signaling and the incidence of MACE has been postulated. Moreover, recently published data suggest an association between thyroid hormone concentration and the risk of sudden cardiac death (SCD) even in euthyroid populations with high-normal FT4 levels. In this study, we investigated markers of repolarization in ECGs, as predictors of cardiovascular events, in patients with a spectrum of subclinical and overt thyroid dysfunction.

Methods: Resting ECGs of 100 subjects, 90 patients (LV-EF > 45%) with thyroid disease (60 overt hyperthyroid, 11 overt hypothyroid and 19 L-T4-treated and biochemically euthyroid patients after thyroidectomy or with autoimmune thyroiditis) and 10 healthy volunteers were analyzed for Tp-e interval. The Tp-e interval was measured manually and was correlated to serum concentrations of thyroid stimulating hormone (TSH), free triiodothyronine (FT3) and thyroxine (FT4).

Results: The Tp-e interval significantly correlated to log-transformed concentrations of TSH (Spearman's rho = 0.30, p < 0.01), FT4 (rho = −0.26, p < 0.05), and FT3 (rho = −0.23, p < 0.05) as well as log-transformed thyroid's secretory capacity (SPINA-GT, rho = −0.33, p < 0.01). Spearman's rho of correlations of JT interval to log-transformed TSH, FT4, FT3, and SPINA-GT were 0.51 (p < 1e−7), −0.45 (p < 1e−5), −0.55 (p < 1e−8), and −0.43 (p < 1e−4), respectively. In minimal multivariable regression models, markers of thyroid homeostasis correlated to heart rate, QT, Tp-e, and JT intervals. Group-wise evaluation in hypothyroid, euthyroid and hyperthyroid subjects revealed similar correlations in all three groups.

Conclusion: We observed significant inverse correlations of Tp-e and JT intervals with FT4 and FT3 over the whole spectrum of thyroid function. Our data suggest a possible mechanism of SCD in hypothyroid state by prolongation of repolarization. We do not observe a U-shaped relationship, so that the mechanism of SCD in patients with high FT4 or hyperthyroidism seems not to be driven by abnormalities in repolarization.

Levothyroxine Treatment and the Risk of Cardiac Arrhythmias - Focus on the Patient Submitted to Thyroid Surgery

Levothyroxine (LT4) is used to treat frequently encountered endocrinopathies such as thyroid diseases. It is regularly used in clinical (overt) hypothyroidism cases and subclinical (latent) hypothyroidism cases in the last decade. Suppressive LT4 therapy is also part of the medical regimen used to manage thyroid malignancies after a thyroidectomy. LT4 treatment possesses dual effects: substituting new-onset thyroid hormone deficiency and suppressing the local and distant malignancy spreading in cancer. It is the practice to administer LT4 in less-than-high suppressive doses for growth control of thyroid nodules and goiter, even in patients with preserved thyroid function. Despite its approved safety for clinical use, LT4 can sometimes induce side-effects, more often recorded with patients under treatment with LT4 suppressive doses than in unintentionally LT4-overdosed patients. Cardiac arrhythmias and the deterioration of osteoporosis are the most frequently documented side-effects of LT4 therapy. It also lowers the threshold for the onset or aggravation of cardiac arrhythmias for patients with pre-existing heart diseases. To improve the quality of life in LT4-substituted patients, clinicians often prescribe higher doses of LT4 to reach low normal TSH levels to achieve cellular euthyroidism. In such circumstances, the risk of cardiac arrhythmias, particularly atrial fibrillation, increases, and the combined use of LT4 and triiodothyronine further complicates such risk. This review summarizes the relevant available data related to LT4 suppressive treatment and the associated risk of cardiac arrhythmia.

Thyroid cancer, recent advances in diagnosis and therapy

Over the past several decades, the approach to the diagnosis and management of patients with follicular cell-derived thyroid cancer has evolved based on improved classification of patients better matching clinical outcomes, as well as advances in imaging, laboratory, molecular technologies and knowledge. While thyroid surgery, radioactive iodine therapy and TSH suppression remain the mainstays of treatment, this expansion of knowledge has enabled de-escalation of therapy for individuals diagnosed with low-risk well-differentiated thyroid cancer; better definition of treatment choices for patients with more aggressive disease; and improved ability to optimize treatments for patients with persistent and/or progressive disease. Most recently, the advancement of knowledge regarding the molecular aspects of thyroid cancer has improved thyroid cancer diagnosis and has enabled individualized therapeutic options for selected patients with the most aggressive forms of the disease. Guidelines from multiple societies across the world reflect these changes, which focus on taking a more individualized approach to clinical management. In this review, we discuss the current more personalized approach to patients with follicular cell-derived thyroid cancer and point toward areas of future research still needed in the field.