A simple test of one minute heart rate variability during deep breathing for evaluation of sympatovagal imbalance in hyperthyroidism.
BACKGROUND
Heart rate variability is a sensitive marker of cardiac sympathetic activity.


OBJECTIVE
To determine whether long-term hyperthyroidism induced by thyroxine suppressive therapy affects HRV.


METHODS
Nineteen patients treated with suppressive doses of thyroxin for thyroid cancer and 19 age-matched controls were enrolled. Thyroid function tests and 1 minute HRV were performed on all subjects and the results were compared between the groups. The 1 minute HRV was analyzed during deep breathing and defined as the difference in beats/minute between the shortest and the longest heart rate interval measured by eletrocardiographic recording during six cycles of deep breathing.


RESULTS
One minute HRV during deep breathing was significantly lower among thyroxine-treated patients compared to healthy controls (25.6 +/- 10.5 vs. 34.3 +/- 12.6 beats/min, P < 0.05). There were no significant differences in mean, maximal and minimal heart rate between the groups.


CONCLUSIONS
Thyroxine therapy administered for epithelial thyroid cancer resulted in subclinical hyperthyroidism and significantly decreased HRV due to autonomic dysfunction rather than basic elevated heart rate.
Shuvy
Mony
M
Heart Institute, Hadassah-Hebrew University Medical Center, Jerusalem, Israel. monysh@gmail.com
Arbelle
Jonathan E
JE
Grosbard
Aviva
A
Katz
Amos
A
D000328:Adult; D004562:Electrocardiography; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D006980:Hyperthyroidism / Q000139:chemically induced / Q000503:physiopathology*; D008875:Middle Aged; D012119:Respiration; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D013964:Thyroid Neoplasms / Q000188:drug therapy; D013974:Thyroxine / Q000627:therapeutic use*; D014630:Vagus Nerve / Q000503:physiopathology*
D013974:Thyroxine