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

Abstract

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.

Diabetes and subclinical hypothyroidism on heart rate variability

“…As regards SCH, we did not observe HRV differences compared with control subjects, which proved to be similar to our previous findings 35 . In another investigation from our research group, we detected impaired autonomic regulation in SCH at rest and following orthostatic manoeuver, but using nonlinear HRV analysis 14 .…”

“…34 As regards SCH, we did not observe HRV differences compared with control subjects, which proved to be similar to our previous findings. 35 In another investigation from our research group, we detected impaired autonomic regulation in SCH at rest and following orthostatic manoeuver, but using nonlinear HRV analysis. 14 Galetta et al 13 and Sahin et al 12 found an association between low global variability (SDNN) and TSH levels in SCH patients compared with controls.…”

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

“…As the cardiovascular system is a major target for thyroid hormone action, [6] all aspects of cardiovascular homeostasis are affected by thyroid hormones, including myocardial contractility, cardiac rhythm, peripheral vascular resistance, and blood flow. [7] Autonomic disturbances are common in patients with thyroid diseases, even in subclinical conditions, [8,9] and it has been suggested that clinical impairments in subclinical hypothyroidism (SCHypo) may precede cardiac dysfunctions. [10–12] However, some regulatory function disturbances of the ANS in subclinical thyroid dysfunctions may be slightly perceptible, requiring some stimulus to appear.…”

Identifying patterns of diurnal blood pressure variation among ELSA‐Brasil participants

“…The following covariates were included in the analysis, considering ; smoking (never, past, or current) 21,28 ; consumption of alcohol (not consuming, moderate-consumption <210 and <140 g/wk for men and women, respectively, excessive-higher than previous consumption limits) 29,30 ; physical activity in leisure time (weak, moderate, and strong following the classification of the International Physical Activity Questionnaire, in the domain of leisure time physical activity) 27,28 ; and body mass index (BMI) (eutrophic = BMI < 25; overweight BMI ≥ 25 to <30; obese ≥30 kg/m 2 ). 28…”