Evaluation of autonomic activity in patients with subclinical hypothyroidism

Abstract

It has been shown that impaired cardiac autonomic activity is closely related with lethal arhythmias. Heart rate variability (HRV), analysis of beat-to-beat variations, is an important and widely used non-invasive method to assess autonomic function. Impaired cardiac autonomic activity and altered sympathovagal balance were previously documented in patients with hypothyroidism. However, the effect of subclinical hypothyroidism (SH) on autonomic function has not been studied yet. We aimed to investigate the effect of SH on sympathovagal balance using the HRV method. The study included 31 patients with SH and 28 healthy volunteer controls. Patients with cardiac, metabolic, neurological disease or any other systemic disease that could affect autonomic activity were excluded from the study. HRV time domain and frequency domain parameters were determined over a period of 24 h. All time and frequency domain measures of HRV in patients with SH were not significantly different compared to those of healthy control group (p > 0.05). Additionally, we compared SH subgroups (TSH level > or =10 and TSH level <10 mU/l) with each other and the controls. A statistically significant difference was observed only in time domain parameters of SD of normal-to-normal intervals (SDNN) and SD of all 5-min mean normal NN intervals (SDANN) between subgroup with TSH level > or =10 and controls (p < 0.05, p < 0.05, respectively). In correlation analysis with TSH, there was positive relationship between TSH and the root mean square of successive differences between adjacent R-R intervals (rMSSD). These findings indicate that SH may affect cardiac autonomic activity in correlation with TSH levels.

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

“…In the study of Sahin et al (15), no differences in LF and HF were found, whereas decreased SDNN was reported in the subgroup with TSH levels equal to or higher than 10 mIU/mL (N=13; 41.9% of total subclinical hypothyroidism group). In our sample, most cases of SCHypo were mild cases, with only 25 (0.27%) subjects presenting TSH levels higher than 10 mIU/L.…”

“…Although some heterogeneity exists, most studies on subclinical thyroid disorders reported an autonomic imbalance with lower HRV indices in both subclinical hyperthyroidism (SCHyper) (10–12) and hypothyroidism (SCHypo) (13–15). Evaluating the relationship between the subclinical dysfunctions and HRV may depict an important scenario regarding the underlying cardiovascular risk in this population.…”

Early textural and functional alterations of left ventricular myocardium in mild hypothyroidism

“…Cardiovascular system is very sensitive to minimal defects of circulating thyroid hormones, and cardiovascular disorders are usually associated with overt hypothyroidism (6)(7)(8). Furthermore, the abnormalities in myocardial contractility and the changes of the lipoprotein profile that are frequently documented in hypothyroid patients have been reported (6,8,9). Therefore, sHT may be considered a true risk factor for the development of coronary heart disease (6)(7)(8)(9)(10)(11)(12)(13).…”

Influência do exercício físico nas alterações cardiovasculares induzidas pelo hipotireoidismo

“…(12) Este aumento está associado com os níveis das catecolaminas plasmáticas e índice de dispersão do segmento QT. (11,25,(54)(55) Akcakoyun et al (10) investigaram a influên-cia do hipotireoidismo subclínico na resposta ao exercício físico em termos de recuperação da frequência cardíaca e competência cronotrópica.…”

“…(1,(4)(5) As disfunções cardiovasculares já são observadas no hipotireoidismo subclínico (2) , pois, uma produção inadequada de TSH tem sido associada com maiores valores de pressão arterial sistólica e diastólica (6) , disfunção endotelial (7)(8) , estresse oxidativo (9) e desbalanço simpatovagal. (10)(11)(12) O exercício físico tem sido indicado como tratamento não farmacológico para doenças crônico-degenerativas como a hipertensão arterial, o diabetes e a obesidade. (13)(14)(15) Além de ser capaz de reduzir pressão arterial, a glicemia em jejum e a gordura corporal, vários estudos demonstram que o exercício físico melhora a função endotelial, a resistência vascular periférica e o balanço simpatovagal de hipertensos, diabéticos e obesos.…”