Power Spectral Analysis of Heart Rate Variability In Hypothyroidism.

ABSTRACT

Background: Hypothyroidism is one of the common clinical problems with high incidence in women particularly in older age. It has profound effect on metabolic processes in almost all tissue of the body and heart is particularly sensitive to thyroid hormone action. Power spectral analysis (PSA)is useful to determine the cardiac autonomic regulation by assessing sympathovagal balance. Objectives: To assess the cardiac autonomic nervous activity by power spectral analysis of heart rate variability in patients with hypothyroidism.Method: This cross sectional study was carried out in the Department of Physiology, Banghabandhu Sheikh Mujib Medical University from 1st July 2008 to 30th June 2009 on 60 female patients of 30-50 years with hypothyroidism (group B). For comparison, 30 age sex matched apparently healthy euthyroid subjects (group A) were also studied. Based on treatment, hypothyroid patients were divided into B1 (patients on their 1st day of diagnosis, before starting of treatment) and B2 (patients with medication for 12-18 months). The patients were selected from the Out Patients Department of Endocrinology, BSMMU. Serum TSH and FT4 levels of all subjects were measured by AxSYM system. To perform power spectral analysis of HRV Total Power(TP), Low Frequency(LF),High Frequency(HF),LF norms (nu),HF norms (nu) and LF/HF ratio were assessed by a Polyrite. For statistical analysis of data, Independent Sample t test, One Way ANOVA and Pearson’s correlation coefficient test were done as applicable.Results: The mean serum TSH(38.16 vs2.18;2.04) was significantly higher and FT4(5.12vs 15.13; 15.08) was significantly lower(p<0.001) in group B1 than those of group A and B2.The mean values of all the spectral parameters of HRV in euthyroid subjects were within normal range. In untreated hypothyroid patients the mean values of TP ( 77.11vs2702.87;2683.73), HF power(56.68 vs 342.02; 437.34) HF nu( 24.79 vs 36.35;34.55) were found significantly (p<0.001) lower LF/HF(1.7±0.3,3.16±.84 and 1.93±.58) and LF nu(75.32 vs 63.71, and 65.90) were significantly (p<0.001) higher and in comparison to both euthyroids and treated patients. Conclusion: Alteration in cardiac autonomic nervous activity characterized by reduced vagal modulation and higher sympathetic activity may occur in the hypothyroid patients..