Changes in autonomic regulation and ventricular repolarization induced by subclinical hyperthyroidism

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.

Deciphering the roles of triiodothyronine (T3) and thyroid-stimulating hormone (TSH) on cardiac electrical remodeling in clinical and experimental hypothyroidism

Hypothyroidism is the most frequent endocrine pathology. Although clinical or overt hypothyroidism has been traditionally associated to low T3 / T4 and high thyrotropin (TSH) circulating levels, other forms exist such as subclinical hypothyroidism, characterized by normal blood T3 / T4 and high TSH. In its different forms is estimated to affect approximately 10% of the population, especially women, in a 5:1 ratio with respect to men. Among its consequences are alterations in cardiac electrical activity, especially in the repolarization phase, which is accompanied by an increased susceptibility to cardiac arrhythmias. Although these alterations have traditionally been attributed to thyroid hormone deficiency, recent studies, both clinical trials and experimental models, demonstrate a fundamental role of TSH in cardiac electrical remodeling. Thus, both metabolic thyroid hormones and TSH regulate cardiac ion channel expression in many and varied ways. This means that the different combinations of hormones that predominate in different types of hypothyroidism (overt, subclinic, primary, central) can generate different forms of cardiac electrical remodeling. These new findings are raising the relevant question of whether serum TSH reference ranges should be redefined.

Heart Rate Variability in Hyperthyroidism: A Systematic Review and Meta-Analysis

Objective: Cardiovascular effects of thyroid hormones may be measured through heart rate variability (HRV). We sought to determine the impact of hyperthyroidism on HRV. Design: A systematic review and meta-analysis on the impact of hyperthyroidism on HRV. Methods: PubMed, Cochrane, Embase and Google Scholar were searched until 20 August 2021 for articles reporting HRV parameters in untreated hyperthyroidism and healthy controls. Random-effects meta-analysis was stratified by degree of hyperthyroidism for each HRV parameter: RR intervals (or Normal-to-Normal intervals—NN), SDNN (standard deviation of RR intervals), RMSSD (square root of the mean difference of successive RR intervals), pNN50 (percentage of RR intervals with >50 ms of variation), total power (TP), LFnu (low-frequency normalized unit) and HFnu (high-frequency), VLF (very low-frequency), and LF/HF ratio. Results: We included 22 studies with 10,811 patients: 1002 with hyperthyroidism and 9809 healthy controls. There was a decrease in RR (effect size = −4.63, 95% CI −5.7 to −3.56), SDNN (−6.07, −7.42 to −4.71), RMSSD (−1.52, −2.18 to −0.87), pNN50 (−1.36, −1.83 to −0.88), TP (−2.05, −2.87 to −1.24), HFnu (−3.51, −4.76 to −2.26), and VLF power (−2.65, −3.74 to −1.55), and an increase in LFnu (2.66, 1.55 to 3.78) and LF/HF ratio (1.75, 1.02 to 2.48) (p < 0.01). Most parameters had ES that was twice as high in overt compared to subclinical hyperthyroidism. Increased peripheral thyroid hormones and decreased TSH levels were associated with lower RR intervals. Conclusions: Hyperthyroidism is associated with a decreased HRV, which may be explained by the deleterious effect of thyroid hormones and TSH. The increased sympathetic and decreased parasympathetic activity may have clinical implications.

A Prolonged QTc Interval Leads to the Diagnosis of Hyperthyroidism in an Adolescent Boy

BACKGROUND

Syncope is a common cause of pediatric emergency department visits and carries a broad differential diagnosis, which includes a few rare but critical cardiac conditions.

CASE REPORT

We review the case of an adolescent boy who presented to the emergency department after a syncopal event. He was found to have a prolonged QTc interval on electrocardiogram (ECG), without personal or family history or known risk factors. He was screened for thyroid dysfunction on a second ED visit for presyncope and was subsequently diagnosed with hyperthyroidism. The patient was treated with methimazole for 2 weeks and a repeat ECG showed normalization of the QTc interval with a QTc reduction of more than 100 ms; routine thyroid studies showed correction of thyroid stimulating hormone and free thyroxine levels shortly thereafter. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: This case and review of the medical literature should raise awareness for the emergency physician to consider evaluation of thyroid function in pediatric patients with QT interval prolongation and vice versa, potentially averting dangerous dysrhythmias.

The assessment of Tp-e interval and Tp-e/QT ratio in patients with hyperthyroidism before and after thyroid surgery

BACKGROUND

Ventricular repolarisation is assessed using the Tp-e interval and QT interval corrected by the heart rate (QTc) via an electrocardiogram (ECG). Prolonged Tp-e/QTc is related with an increased risk of arrhythmias and cardiac mortality.

OBJECTIVE

This study was conducted at a single centre in collaboration with general surgery and cardiology clinics. We aimed to appraise the assessment of Tp-e interval and Tp-e/QT ratio in patients with hyperthyroidism before and after thyroid surgery.

METHODS

Totally 65 patients with hyperthyroidism before and after thyroid surgery were enrolled in our study. In presurgical hospitalisation and six months after the thyroid surgery, we measured the electrocardiographic parameters again on same patients. All subjects who were investigated in this study were in sinus rhythm. Tp-e interval, Tp-e/QT and Tp-e/QTc ratios were measured from the 12-lead electrocardiogram.

RESULTS

Heart rate (P = .073), QT interval (P = .432) and QTc interval (P = .179) were similar before and after thyroid surgery. Tp-e interval (84.6 ± 13.1 vs 77.2 ± 10.9; P = .031), Tp-e/QT ratio (0.23 ± 0.04 vs 0.21 ± 0.04; P < .001), Tp-e/QTc ratio (0.21 ± 0.04 vs 0.19 ± 0.03; P < .001) and QTc dispersion (52.4 ± 7.2 vs 48.4 ± 7.4; P < .001) were significantly different before and after thyroid surgery. In correlation analysis, there was a significant correlation between preprocedural Tp-e/QTc ratio and preprocedural fT4 in patients with hyperthyroidism (r = 0.275, P = .026).

CONCLUSION

Our study demonstrated that Tp-e interval, Tp-e/QT and Tp-e/QTc ratios were shortened in patients with hyperthyroidism after thyroid surgery than before procedure. This study is considerable to display that hyperthyroidism may have a negative effect on cardiac conduction system, which potentially may induce formation of ventricular arrhythmias.

Excessive daytime sleepiness and its predictors among medical and health science students of University of Gondar, Northwest Ethiopia: institution-based cross-sectional study

Background

Excessive daytime sleepiness (EDS) is a condition of sleepiness when a person would not be expected to sleep. University students are prone to EDS due to the competitive learning environment and fragmented night sleep. No study was conducted in Ethiopia on EDS. Therefore, this study aimed to determine EDS and its predictors among University of Gondar (UoG) Medical and Health Science students.

Methods

Institution-based cross-sectional study was carried out on 383 Medical and Health Science students of UoG who were recruited using a computer-generated simple random sampling technique. We used a validated Epworth daytime sleepiness tool to collect data. Epi-Info™ 7 and Stata 14 were used for data entry and analysis, respectively. Bivariable and multivariable binary logistic regression analyses were performed to find out predictors. Odds ratio with 95% uncertainty interval were computed. In the final model, a variable with a p < 0.05 was declared as a predictor of EDS.

Results

Three hundred and eighty-three students completed the questionnaire. Males were 69.97% and the mean age of participants was 20.79 (±1.83) years. In the current study, the prevalence of EDS was 31.07% (95% UI: 26.62–35.91). The odds of getting EDS was 1.83 (AOR = 1.83, 95% UI: 1.14–2.96) and 1.84 (AOR = 1.84, 95% UI: 1.13–3.00) higher among students who reported night sleep behaviour disorders and depression, respectively.

Conclusion

This study revealed that EDS is high and predicted by depression and night sleep behaviour disorders. These findings suggest the need to set preventive strategies such as counselling of students to reduce depression and night sleep behaviour disorders. Further studies particularly qualitative studies are required to find out more factors affecting EDS.

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

The effects of thyrotropin (TSH) suppressive therapy on autonomic regulation and ventricular repolarization in patients with differentiated thyroid cancer (DTC) have not been elucidated. The aim of present study was to evaluate variation in heart rate variability (HRV) and QT dispersion after TSH suppressive therapy in patients with DTC.Cases, defined as 271 patients with DTC within 1 year of exogenous levothyroxine, and all patients underwent a full history, physical examination, including standard 12 lead electrocardiogram (ECG), and 24 h ambulatory ECG monitoring (Holter) with normal free thyroxine (FT4) and free triiodothyronine (FT3) with levothyroxine. To evaluate effects of TSH suppressive therapy on HRV and QT dispersion, patients were divided into three groups according to different levels of TSH: TSH < 0.1 mIU/L group and 0.1 ≤ TSH < 0.5 mIU/L group were as TSH suppression groups, and 0.5 ≤ TSH < 2.0 mIU/L group was as TSH replacement group.Comparing with 0.5 ≤ TSH < 2.0 mIU/L group, significant changes in both time and frequency domain of HRV and QT dispersion were observed in TSH < 0.1 mIU/L group (P < .001: SDNN, SDANN, HF, LF/HF, QTd, and QTcd; P < .05: rMSSD) and 0.1 ≤ TSH < 0.5 mIU/L group (P < .001: SDNN, HF, LF/HF, QTd, and QTcd), and especially were more pronounced in TSH < 0.1 mIU/L group. Moreover, we found that TSH level was proportional to SDNN (β = 15.829, P < .001), but inversely proportional to LF/HF (β = -0.671, P < .001), QTd (β = -16.674, P < .001) and QTcd (β = -18.314, P < .001) in DTC patients with exogenous levothyroxine.Compared with euthyroid state, patients with suppressed serum TSH have increased sympathetic activity in the presence of diminished vagal tone, ultimately showed sympathovagal imbalance and with an increased inhomogeneity of ventricular recovery times. These findings revealed that TSH suppression therapy had a significant impact on cardiovascular system and had certain guiding role in the treatment and management of patients with DTC.

Linear and nonlinear analyses of heart rate variability following orthostatism in subclinical hypothyroidism

Subclinical hypothyroidism (SCHypo) is associated with autonomic disturbances that can interfere in physiological responses. This study was designed to evaluate linear and nonlinear variables of heart rate variability (HRV) following postural change, comparing subjects with SCHypo to euthyroid subjects.HRV analyses were performed in 5-minute time series collected in the supine and standing positions from a subsample of 855 participants of the ELSA-Brasil study. The cardiac autonomic nervous function was evaluated by linear time and frequency domain analyses (SDNN, RMSSD, LFms, HFms, and LF/HF ratio) as well as by nonlinear symbolic dynamics (0, 1, and 2 V).After exclusions, 509 (92.0%) euthyroid and 44 (8.0%) SCHypo participants were eligible for analyses. At the baseline supine rest measurement, the 0 V symbolic pattern was higher (27.7 vs 25.4, P = .02) and 2 V was lower (18.0 vs 22.9, P = .02) than in the euthyroid group. Comparing the variation between positions, the 0 V pattern showed a lower delta in SCHypo than in Euthyroid subjects (8.0 vs 10.8%, P = .04).SCHypo presented lower sympathetic and parasympathetic tonus at rest and a blunted sympathetic response to active postural change, marked by reduced variation in the 0 V of symbolic analysis (SA). Additionally, it is suggested that SA of HR dynamics is an alternative and, possibly, a more sensitive method for cardiac autonomic assessment following orthostatism in this population.

Relationship between heart rate variability and subclinical thyroid disorders of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

The association between subclinical thyroid dysfunctions and autonomic modulation changes has been described by many studies with conflicting results. We aimed to analyze the association between subclinical hyperthyroidism (SCHyper), subclinical hypothyroidism (SCHypo), and heart rate variability (HRV) using the baseline from ELSA-Brasil. SCHyper and SCHypo were classified by use of medication to treat thyroid disorders, thyrotropin levels respectively above and under the reference range, and normal free thyroxine levels. For HRV, the participants underwent 10 min in supine position and the R-R intervals of the final 5 min were selected for analysis. We first used linear regression models to report crude data and then, multivariate adjustment for sociodemographic (age, sex, and race) and cardiovascular risk factors (hypertension, dyslipidemia, diabetes, smoking, body mass index, use of alcohol, and leisure physical activity) using the euthyroid group as reference. From 9270 subjects (median age, 50; interquartile range: 44–56), 8623 (93.0%) were classified as euthyroid, 136 (1.5%) as SCHyper, and 511 (5.5%) as SCHypo. Compared to euthyroid subjects, SCHyper participants presented significantly higher heart rate (68.8 vs 66.5 for euthyroidism, P=0.007) and shorter R-R intervals (871.4 vs 901.6, P=0.007). Although SCHyper was associated with lower standard deviation of NN interval (SDNN) (β: –0.070; 95% confidence interval (95%CI): –0.014 to –0.009) and low-frequency (LF) (β: –0.242, 95%CI: –0.426 to –0.058) compared to the euthyroid group, these differences lost significance after multivariate adjustment for confounders. No significant differences were found for HRV in SCHypo. No association was found between HRV and SCHyper or SCHypo compared to euthyroid subjects in this sample of apparently healthy subjects.

The corrected QT (QTc) prolongation in hyperthyroidism and the association of thyroid hormone with the QTc interval

Purpose

Ventricular repolarization is assessed using the QT interval corrected by the heart rate (QTc) via an electrocardiogram (ECG). Prolonged QTc is associated with an increased risk of arrhythmias and cardiac mortality. As there have been few reports regarding the effects of hyperthyroidism on ventricular repolarization, we studied the association between serum free thyroxine (free T4 [fT4]) and thyroid stimulating hormone (TSH) levels and the QTc interval.

Methods

Thirty-eight patients with hyperthyroidism (<30 years old) were included, and we used their clinical records and available ECGs (between August 2003 and August 2011) to evaluate the association between their fT4 and TSH levels and their QTc interval. In addition, we studied the ECGs of 72 age-matched patients with no hyperthyroidism (control group) and compared their data with that from the patients group.

Results

The QTc duration in patients with hyperthyroidism was significantly prolonged compared to that in the control subjects (P<0.001). In addition, the number of hyperthyroid patients with abnormal prolonged QTc was significantly higher than that in the control group (P<0.001). Among the patients with hyperthyroidism, patients with prolonged QTc and borderline QTc had higher fT4 levels and there was positive correlation between their fT4 levels and their QTc interval (P<0.05). However, no correlation was observed between their TSH levels and their QTc interval.

Conclusion

We report that hyperthyroidism is associated with QTc prolongation. The correlation between the fT4 levels and the QTc interval suggests that thyroid status is associated with QTc values and the risk of cardiac mortality.

QT prolongation in a child with thyroid storm

A 12-year-old girl presented with an acute confusional state and a 2-year history of weight loss, anxiety, agitation and recurrent fever. Thyroid function tests confirmed severe hyperthyroidism, and a diagnosis of thyroid storm was made (Burch and Wartofsky score=75). ECG showed a prolonged QTc interval of 506 ms. Acute treatment for thyroid storm consisted of Lugol's iodine, prednisolone, carbimazole and propranolol. She made a steady recovery and by 3 months her thyroid function had normalised; a repeat ECG showed a QTc within the normal range (430 ms). There was no relevant family history. This is a case of QTc prolongation with hyperthyroidism and normalisation with euthyroidism. It is not commonly recognised that hyperthyroidism in children may be associated with QTc prolongation. QTc measurement should be incorporated into management protocols for hyperthyroidism.

Metformin-induced thyrotropin suppression is not associated with cardiac effects

OBJECTIVE

Metformin treatment may induce a decrease/suppression in serum TSH levels, mimicking sub-clinical hyperthyroidism (SHT). The aim of the present study was to retrospectively evaluate changes in several electrocardiographic indices in euthyroid subjects with diabetes who, after starting metformin treatment, developed a low serum TSH as compared to patients with SHT resulting from an underlying thyroid disease or TSH suppressive treatment with L-thyroxine.

DESIGN

Heart rate, P wave duration, P wave dispersion, QTmax, QTmin and QT-dispersion were assessed in 23 patients with diabetes treated with metformin before and after 6 months of TSH-suppression and in 31 control patients with SHT.

RESULTS

No significant changes in electrocardiographic parameters were observed from baseline to the TSH-suppression measurement. A significant difference in P wave duration (102.9 ± 7.4 vs. 92.1 ± 5.8 ms, p<0.001), P wave dispersion (13.1 ± 3.4 vs. 7.1 ± 3.5 ms, p<0.001), QTmax (399 ± 18 vs. 388 ± 16 ms, p=0.024), QTmin (341 ± 14 vs. 350 ± 17 ms, p=0.038) and QT dispersion (49.9 ± 9.6 vs. 30.9 ± 9.2 ms, p<0.001) were observed between the control group with SHT and the group of diabetic patients with low serum levels of TSH.

CONCLUSIONS

Our results show that the TSH-suppressive effect observed in patients taking metformin is not associated with peripheral markers of thyroid hormone excess, at least at the cardiac level.

Hyperthyroidism and cardiovascular complications: a narrative review on the basis of pathophysiology

Cardiovascular complications are important in hyperthyroidism because of their high frequency in clinical presentation and increased mortality and morbidity risk. The cause of hyperthyroidism, factors related to the patient, and the genetic basis for complications are associated with risk and the basic underlying mechanisms are important for treatment and management of the disease. Besides cellular effects, hyperthyroidism also causes hemodynamic changes, such as increased preload and contractility and decreased systemic vascular resistance causes increased cardiac output. Besides tachyarrythmias, impaired systolic ventricular dysfunction and diastolic dysfunction may cause thyrotoxic cardiomyopathy in a small percentage of the patients, as another high mortality complication. Although the medical literature has some conflicting data about benefits of treatment of subclinical hyperthyroidism, even high-normal thyroid function may cause cardiovascular problems and it should be treated. This review summarizes the cardiovascular consequences of hyperthyroidism with underlying mechanisms.