Relationship of Thyroid Hormones with Heart Rate Variability

Abstract

Background: Altered thyroid functions are associated with variation in autonomic regulation of
cardiovascular activity. Cardiac Autonomic Nervous Activity (CANA) can be assessed quantitatively
by analysis of Heart Rate Variability (HRV). Objective: To observe the relationship between CANA
with altered TSH and FT4. Methods: This cross sectional study was carried out in the Department of
Physiology, BSMMU, Dhaka between1st July 2007 and 30th June 2008 on 60 patients with excess
thyroid hormone (group B, aged 30-50 years). Based on treatment, 30 untreated newly diagnosed
patients were designated as group B₁ and 30 patients under treatment with antithyroid drugs for at
least 2 months were included into group B₂ in order to observe the effect of treatment. All these
patients were selected from the Out Patient Department of Endocrinology wing of Department of
Medicine, BSMMU, Dhaka. Sociodemographically matched 20 apparently healthy euthyroid persons
were selected for comparison (group A). To confirm thyroid status, serum TSH and serum FT₄ levels
were measured by AxSym system and some of the spectral HRV parameters i.e.mean R-R interval,
mean heart rate, variance, LF n.u, HF n.u and LF/HF ratio were assessed by recordings of ECG for 5
minute (short term) with a polyrite. For statistical analysis Pearson’s correlation coefficient (r) test was
used. Results: With serum TSH level, the LF n.u. power and LF/HF ratio showed significant (p<0.05)
positive correlations but HF n.u. power showed significant (p<0.05) negative correlation in group B₁.
But these three parameters showed non significant correlations with TSH in the other two groups (A,
B₂). Similarly with serum TSH level, variance and mean R-R interval showed negative and mean HR
showed positive correlation in group B₁. In group A, all these parameters were positively correlated
whereas in group B₂, RR interval and variance were positively and mean HR was negatively correlated.
All these correlations were statistically non significant. With serum FT₄ levels, mean R-R and HF n.u.
were negatively and mean heart rate, LFnu, LF/HF were positively correlated in all three groups but
variance showed positive in group A and negative correlation in B₁ and B₂. All these correlations were
statistically non significant. Conclusion: From this study it can be concluded that changes in autonomic
nervous regulation are related to altered serum level of TSH and FT₄ in hyperthyroids.

Key words: HRV; LF; HF; RR interval; Hyperthyroid

DOI: 10.3329/jbsp.v5i1.5414

J Bangladesh Soc Physiol. 2010 June; 5(1): 20-26