Altered cardiovascular vagal responses in nonelderly female patients with subclinical hyperthyroidism and no apparent cardiovascular disease.
OBJECTIVE
Subclinical hyperthyroidism (SH) has been associated with exercise intolerance, changes in cardiac morphology, atrial arrhythmias and sympathovagal imbalance. The aim of this study was to evaluate the vagal reserve and modulation by a sympathetic stimulus in nonelderly patients with SH without cardiovascular problems.


METHODS
We carried out a cross-sectional study, comparing data of the heart rate variability (HRV) of SH patients and healthy controls at rest and after vagal and sympathetic stimulation.


METHODS
We studied 16 female patients with at least 6 months of SH and 16 healthy female controls with the same median age (40 vs. 34.5 years).


METHODS
We used the tilt test, with electrocardiographic record at rest, during the respiratory sinus arrhythmia (RSA) manoeuvre and after tilting, in order to analyse HRV in the frequency domain (%high frequency (HF) and low/high frequency ratio (LF/HF) using Biopotentials Captation System software.


RESULTS
The median TSH level was 0.03 mU/l in patients and 1.37 mUI/l in controls. The median free T4 was 1.37 ng/dl in patients and 1.20 ng/dl in controls. Patients demonstrated a significantly smaller difference between %HF during the RSA and %HF at rest than controls (median -7.5 vs. 36.6, P < 0.001). There was a lower difference between LF/HF ratio after tilting and LF/HF ratio at rest in patients than in controls (1.5 vs. 5.3, P = 0.005).


CONCLUSIONS
Subclinical hyperthyroidism affects cardiovascular autonomic balance in otherwise apparently healthy nonelderly females by blunting vagal responses.
Portella
Renata Boschi
RB
Endocrine Service and Cardiology Service of the Federal University of Rio de Janeiro, Av. Oswaldo Cruz 73/2201 Flamengo, Rio de Janeiro, Brazil. portella@novanet.com.br
Pedrosa
Roberto Coury
RC
Coeli
Claudia Medina
CM
Buescu
Alexandru
A
Vaisman
Mario
M
D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology*; D002319:Cardiovascular System / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood / Q000503:physiopathology*; D008875:Middle Aged; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D018667:Tilt-Table Test; D014630:Vagus Nerve / Q000503:physiopathology
D013972:Thyrotropin; D013974:Thyroxine