Heart rate variability and its response to thyroxine replacement therapy in patients with hypothyroidism

Objective To analyze heart rate variability (HRV)and its changes with thyro xine treatment in patients with hypothyroidism. Methods HRV was analyzed using 24-hour electrocardiographic recording in 38 patients with hypothyroidism and 21 normal controls. The changes in HRV we re evaluated for the 18 hypothyroid patients after 3 months of thyroxine th erapy. Results The time domain measurements of HRV in hypothyroid patients were mu ch lower than those in the control group. As to HRV frequency domain, the h igh frequency power was significantly higher, but the ratio of low frequenc y power to frequency power for hypothyroid patients was lower than in the c ontrols. These abnormal changes of HRV measurements in hypothyroid patients were improved after treatment with thyroxine and were associated with reco very of serum concentrations of FT3 and FT4. Conclusions Patients with hypothyroidism often have autonomic neuropathies with a higher level of vagal tone. These abnormalities could be partly impr oved by thyoxine therapy.