Altered cardiovascular vagal responses in nonelderly female patients with subclinical hyperthyroidism and no apparent cardiovascular disease

• Published in: Clinical endocrinology (Oxford) Vol. 67; no. 2; pp. 290 - 294
• Main Authors: Portella, Renata Boschi, Pedrosa, Roberto Coury, Coeli, Claudia Medina, Buescu, Alexandru, Vaisman, Mario
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.08.2007; Blackwell
• Subjects: Adult; Autonomic Nervous System - physiopathology; Biological and medical sciences; Cardiovascular System - physiopathology; Cross-Sectional Studies; Electrocardiography; Endocrinopathies; Female; Fundamental and applied biological sciences. Psychology; Heart Rate - physiology; Humans; Hyperthyroidism - blood; Hyperthyroidism - physiopathology; Medical sciences; Middle Aged; Non tumoral diseases. Target tissue resistance. Benign neoplasms; Thyroid. Thyroid axis (diseases); Thyrotropin - blood; Thyroxine - blood; Tilt-Table Test; Vagus Nerve - physiopathology; Vertebrates: endocrinology; Endocrinopathy; Human; Hyperthyroidism; Thyroid diseases; Cardiovascular disease; Female; Patient; Circulatory system; Endocrinology
• ISSN: 0300-0664; 1365-2265
• DOI: 10.1111/j.1365-2265.2007.02879.x

Summary 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. Design  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. Patients  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). Measurements  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). Conclusion  Subclinical hyperthyroidism affects cardiovascular autonomic balance in otherwise apparently healthy nonelderly females by blunting vagal responses.