Cardiac Autonomic Modulation and Anti-Thyroid Peroxidase (TPO) Antibodies in Subclinical Hypothyroidism – Does Any Correlation Exist?

Abstract

Background: Heart rate variability (HRV) reflects the balance between the sympathetic and parasympathetic divisions of the autonomic nervous system. Anti-thyroid antibodies like anti-TPO and anti-Thyroglobulin have long been associated with thyroid dysfunction and abnormal thyroid profile testing. Subclinical hypothyroidism (SCHypo) is characterized by elevated thyroid-stimulating hormone (TSH) with normal thyroid hormones. We hypothesize that autonomic function may be deranged in anti-TPO positive subclinical hypothyroid cases, even before the onset of overt hypothyroidism.Objectives: To investigate the association between anti-Thyroid Peroxidase antibodies (anti-TPOAb) positive SCHypo and sympathovagal imbalance (SVI), if any.Methodology: The study was conducted on the age and body mass index (BMI) matched subclinical hypothyroid patients (n=52) and healthy controls (n=20). The cardiac autonomic activity was assessed by short-term HRV in the time (SDNN, RMSSD, pNN50) and frequency domains (LFms 2 , HFms 2 , LFnu, HFnu, TP, and LF/HF ratio). Nonlinear geometric measures (SD1, SD2, SD1/SD2, TINN, HRV triangular index) were also evaluated. Biochemical evaluation of serum thyroid profile and anti-TPOAb was done in all the subjects. Results: Decreased HRV was observed in the anti-TPOAb positive group when compared to the antibodynegative and control groups. Significant positive correlation of anti-TPOAb with TSH, LFnu, LF/HF and negative correlation with SDNN, RMSSD, pNN50, SD1, SD1/SD2, HFnu, and TP of HRV was observed.Conclusion: Anti-TPOAb positive SCHypo group exhibited modifications in HRV characterized by decreased parasympathetic modulation, as compared to controls. The findings were also suggestive of increased risk of autonomic dysfunction in TPOAb-positive patients, as compared to antibody negative. An increase in anti-TPO antibodies was significantly correlated with TSH and SVI in SCHypo patients.

Fetal cardiac left ventricle functional changes in pregnancies with maternal hypothyroidism

“…27 Both our study and other examples show that subclinical hypothyroidism and especially Anti-TPO positivity in this group have significant effects on the fetal heart. 26,27 Anti-TPO and Anti-TG antibodies that can cross the placenta are present in 3%−18% of pregnancies, and this rate was 16.9% in our study, which is consistent with the literature. 28 In cardiomyocytes, thyroid hormones regulate the β-adrenergic system and reninangiotensin-aldosterone system (RAS).…”

“…reported that the babies of women with subclinical hypothyroidism had higher systolic and diastolic blood pressures than the control group 27 . Both our study and other examples show that subclinical hypothyroidism and especially Anti‐TPO positivity in this group have significant effects on the fetal heart 26,27 …”

“…Mavai et al stated that subclinical hypothyroidism with positive Anti-TPO might cause irregular heart rate variability and sympathovagal imbalance, as a result of which the risk of cardiovascular morbidity and mortality is high in these cases. 26 Rytter et al reported that the babies of women with subclinical hypothyroidism had higher systolic and diastolic blood pressures than the control group. 27 Both our study and other examples show that subclinical hypothyroidism and especially Anti-TPO positivity in this group have significant effects on the fetal heart.…”

“…Mavai et al. stated that subclinical hypothyroidism with positive Anti‐TPO might cause irregular heart rate variability and sympathovagal imbalance, as a result of which the risk of cardiovascular morbidity and mortality is high in these cases 26 . Rytter et al.…”

Impaired autonomic function and somatosensory disturbance in patients with treated autoimmune thyroiditis

“…In contrast, we observed a more pronounced association for functional parameters of the autonomic nervous system. Several studies and animal experiments found altered cardiovascular autonomic function in subclinical or overt hypothyroidism [53][54][55][56][66][67][68][69][70] . However, the evidence for a potential role of autoimmunity in euthyroid subjects is much weaker.…”