Background: Thyroid hormones exert effects on the heart and peripheral circulation. Heart rate variability (HRV) is a good
marker for identifying the cardiovascular risk in patients with hyperthyroidism.
Aims and Objective: To evaluate the impact of hyperthyroidism on autonomic tone and to compare the HRV parameters
in patients with hyperthyroidism and healthy volunteers.
Materials and Methods: This study was conducted at PSG Institute of Medical Sciences and Research, Coimbatore, Tamil
Nadu, on 30 hyperthyroid patients (cases) with average age 39.23 ± 6.91 years and 30 healthy volunteers (controls) with
average age 42.13 ± 6.78 years. After obtaining the written consent from the subjects, ECG was recorded for 10 min in a
computerized physiograph in lead II.
Results: Statistical analysis carried out by independent Students t-test showed a significant difference (P < 0.001) in HRV
parameters of patients with hyperthyroid and healthy volunteers. Among the frequency domain measures, a decrease in
high frequency (HF) in normalized units and increase in low frequency (LF) in normalized units, and in the ratio of LF to HF
(LF/HF) in hyperthyroid patients was observed. Among the time domain measures, decrease in RR intervals, SDNN, RMSSD,
and NN50 was observed in patients with hyperthyroid compared to those with euthyroidism.
Conclusion: This study showed that individuals with hyperthyroidism had a higher sympathetic tone and a lower
parasympathetic tone as compared to those with euthyroidism. Using HRV analysis, we can identify patients who are at risk
for cardiac complications and early intervention can reduce mortality rates.
Key words: Heart Rate Variability (HRV); Hyperthyroidism; Euthyroidism; Autonomic Dysfunction
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