Cardiac Autonomic Nervous System Activity on Hyper and Hypothyroidism

pp 149-157

Abstract

Background

The contribution of autonomic nervous systemdys function to the manifestations of hyper- and hypothyroidism remains unclear. The aim of the present work was to determine whether autonomic nervous system activity (as estimated by heart rate variability analysis) in thyroid patients is different from that of normal individuals.Material and methodWe studied the autonomic function in 20 patients with hyperthyroidism and 10 patients with hypothyroidism.

Results

Hyperthyroid patients exhibited normal cardiac autonomic activity during rest, Valsalva maneuver, and deep breathing. On the other hand, vagal withdrawal during bipedestation was absent in these patients, as indicated by frequency-domain heart rate variability analysis and 30:15 ratio (the latter depending upon transitory changes of heart after a lying-to-standing maneuver). Hypothyroid patients obtained values comparable to those of normal persons in all tests.

Conclusions

The normal or increased cardiac parasympathetic activity in patients with hyperthyroidism may help to explain some of their clinical features, such as the rarity of malignant ventricular arrhythmias and the high incidence of atrial fibrillation.