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Sinus node function in hyperthyroid patients.

R Valcavi1, C Menozzi, E Roti

  • 12a Divisione di Medicina Interna, Arcispedale S. Maria Nuova, Reggio Emilia, Italy.

The Journal of Clinical Endocrinology and Metabolism
|July 1, 1992
PubMed
Summary
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Thyrotoxicosis increases intrinsic sinus node activity, leading to a higher resting heart rate. Autonomic nervous system blockade did not fully explain these changes in hyperthyroid patients.

Area of Science:

  • Cardiology
  • Endocrinology
  • Electrophysiology

Background:

  • Thyrotoxicosis, a condition of excess thyroid hormone, is known to affect cardiovascular function.
  • The precise mechanisms by which thyroid hormone excess influences cardiac electrophysiology, specifically sinus node function, require further elucidation.

Purpose of the Study:

  • To investigate the electrophysiology of the sinus node in patients with thyrotoxicosis.
  • To determine the role of the autonomic nervous system in modulating sinus node function during hyperthyroidism.

Main Methods:

  • Electrophysiological parameters including resting heart rate (RHR), sino-atrial conduction time (SACT), and sinus node recovery time (SNRT) were measured in 8 thyrotoxic patients.
  • Measurements were taken under basal conditions, after sympathetic blockade with propranolol, and after complete autonomic blockade with propranolol and atropine.

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Main Results:

  • Thyrotoxic patients exhibited a significantly higher RHR compared to normal subjects, while SACT and SNRT were not significantly different.
  • Sympathetic blockade resulted in a greater RHR decrease and SACT increase in thyrotoxic patients versus controls.
  • Complete autonomic blockade normalized electrophysiological parameters in thyrotoxic patients to basal levels.

Conclusions:

  • The intrinsic activity of the sinus node is increased in thyrotoxicosis, likely due to direct effects of thyroid hormone excess.
  • The observed alterations in sinus node function are primarily attributed to intrinsic changes rather than extrinsic autonomic nervous system influences.