title: Both hypothyroidism and hyperthyroidism increase atrial fibrillation inducibility in rats.
abstract: BACKGROUND
  Evidence indicates that cardiac hypothyroidism may contribute to heart failure progression. It is also known that heart failure is associated with an increased risk of atrial fibrillation (AF). Although it is established that hyperthyroidism increases AF incidence, the effect of hypothyroidism on AF is unclear. This study investigated the effects of different thyroid hormone levels, ranging from hypothyroidism to hyperthyroidism on AF inducibility in thyroidectomized rats.
  
  
  RESULTS
  Thyroidectomized rats with serum-confirmed hypothyroidism 1 month after surgery were randomized into hypothyroid (N=9), euthyroid (N=9), and hyperthyroid (N=9) groups. Rats received placebo, 3.3-mg l-thyroxine (T4), or 20-mg T4 pellets (60-day release form) for 2 months, respectively. At the end of treatment, hypothyroid, euthyroid, and hyperthyroid status was confirmed. Hypothyroid animals showed cardiac atrophy and reduced cardiac systolic and diastolic functions, whereas hyperthyroid rats exhibited cardiac hypertrophy and increased cardiac function. Hypothyroidism and hyperthyroidism produced opposite electrophysiological changes in heart rates and atrial effective refractory period, but both significantly increased AF susceptibility. AF incidence was 78% in hypothyroid, 67% in hyperthyroid, and the duration of induced AF was also longer, compared with 11% in the euthyroid group (all P<0.05). Hypothyroidism increased atrial interstitial fibrosis, but connexin 43 was not affected.
  
  
  CONCLUSIONS
  Both hypothyroidism and hyperthyroidism lead to increased AF vulnerability in a rat thyroidectomy model. Our results stress that normal thyroid hormone levels are required to maintain normal cardiac electrophysiology and to prevent cardiac arrhythmias and AF.
authors.affiliation: Department of Biomedical Sciences, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, NY.
authors.forename: Youhua
authors.initials: Y
authors.lastname: Zhang
authors.forename: Eduard I
authors.initials: EI
authors.lastname: Dedkov
authors.forename: Diana
authors.initials: D
authors.lastname: Teplitsky
authors.forename: Nathan Y
authors.initials: NY
authors.lastname: Weltman
authors.forename: Christine J
authors.initials: CJ
authors.lastname: Pol
authors.forename: Viswanathan
authors.initials: V
authors.lastname: Rajagopalan
authors.forename: Bianca
authors.initials: B
authors.lastname: Lee
authors.forename: A Martin
authors.initials: AM
authors.lastname: Gerdes
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology; D004195:Disease Models, Animal; D004452:Echocardiography; D022062:Electrophysiologic Techniques, Cardiac; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006439:Hemodynamics; D006980:Hyperthyroidism / Q000150:complications*; D007037:Hypothyroidism / Q000150:complications*; D007150:Immunohistochemistry; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013963:Thyroid Hormones / Q000097:blood; D013965:Thyroidectomy
chemical_list: D013963:Thyroid Hormones
keywords: arrhythmias, cardiac; atrial fibrillation; electrophysiology; thyroid hormones
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