Changes in autonomic regulation and ventricular repolarization induced by subclinical hyperthyroidism

Galetta, Fabio; Franzoni, Ferdinando; Fallahi, Poupak; Tocchini, Leonardo; Graci, F; Gaddeo, Caterina; Rossi, Marco; Cini, G; Carpi, Angelo; Santoro, Gino; Antonelli, Alessandro

doi:10.1016/j.biopha.2009.10.001

Cited by 20 publications

(29 citation statements)

References 23 publications

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“…Accordingly, previous studies with smaller sample sizes showed reduced variability in subjects with SCHyper compared to euthyroid ones (10,11,14,26). Goichot et al (11) detected lower values for SDNN in SCHyper subjects (N=12) compared to controls (N=32).…”

Section: Discussionmentioning

confidence: 86%

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

Miranda

Hoshi

Bittencourt

et al. 2018

Braz J Med Biol Res

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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.

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Section: Discussionmentioning

confidence: 86%

“…By using the Minitab 18 software (Minitab, France), a power of 80% with an alpha of 0.05 was calculated for a sample size of 135 subjects (11,26-28). …”

Section: Methodsmentioning

confidence: 99%

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

Miranda

Hoshi

Bittencourt

et al. 2018

Braz J Med Biol Res

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“…One of the earliest cardiovascular consequences of SHT is the occurrence of a sympathetic-vagal imbalance, characterized by increased sympathetic activity in the presence of a diminished vagal tone. 12,13,17 Owecki et al also showed that, in its early stages, SHT causes alterations of ventricular repolarization, represented by a prolonged QT interval. 18 These electrocardiographic alterations are apparently due to the condition of mild hyperthyroidism, as assessed by the lower than normal serum TSH, rather than to an aetiology of thyrotoxicosis.…”

Section: Discussionmentioning

confidence: 99%

“…Although commonly asymptomatic, SHT is associated with an increased risk of cardiac arrhythmias, mostly atrial fibrillation, morphological and functional cardiac alterations, 12,13 resulting in increased cardiovascular morbidity and mortality. [14][15][16] It was also shown that patients with SHT suffer from a sympathetic-vagal imbalance, characterized by an increased sympathetic activity in the presence of a diminished vagal tone, 12,13,17 and may also display a prolonged QT interval. 18 The aim of the present study was to retrospectively evaluate the heart rate variability in euthyroid subjects with diabetes who, after starting metformin treatment, developed a low serum TSH.…”

Section: Introductionmentioning

confidence: 99%

Metformin-induced thyrotropin suppression is not associated with cardiac effects

et al. 2014

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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.

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“…In adults with hyperthyroidism, QTc is prolonged compared with controls and normalises with treatment of hyperthyroidism, furthermore QTc is positively correlated with both serum FT3 and FT4 9. Those with subclinical hyperthyroidism have longer QTc than controls10 and within the normal male population QTc is correlated with FT4 11. The clinical importance of this effect is suggested by a population-based study in adults which found that the use of antithyroid drugs was associated with sudden cardiac death; the authors proposed that this was due to undertreated hyperthyroidism 12.…”

Section: Discussionmentioning

confidence: 99%

QT prolongation in a child with thyroid storm

et al. 2014

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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.

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Changes in autonomic regulation and ventricular repolarization induced by subclinical hyperthyroidism

Cited by 20 publications

References 23 publications

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

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

Metformin-induced thyrotropin suppression is not associated with cardiac effects

QT prolongation in a child with thyroid storm

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