title: Thyroid hormones and electrocardiographic parameters: findings from the third national health and nutrition examination survey.
abstract: BACKGROUND
  Altered thyroid status exerts a major effect on the heart. Individuals with hypo- or hyperthyroidism showed various changes in electrocardiograms. However, little is known about how variations in thyroid hormone levels within the normal range affect electrical activities of the heart in the general population.
  
  
  RESULTS
  We conducted a cross-sectional analysis of 5,990 men and women from the Third National Health and Nutrition Examination Survey. Serum total T4 was measured by immunoassay and TSH was measured by chemiluminescent assay. We categorized T4 and TSH into 7 groups with cut-offs at the 5(th), 20(th), 40(th), 60(th), 80(th), and 95(th) percentiles of the weighted population distribution. Electrocardiographic parameters were measured from the standard 12-lead electrocardiogram. We found a positive linear association between serum total T4 level and heart rate in men, and a U-shape association between T4 and PR interval in men and women. TSH level was positively associated with QRS interval in men, while a U-shape association between TSH and QRS was observed in women. No clear graded association between thyroid hormones and corrected QT or JT was found, except that men in the highest category of T4 levels appeared to have longer corrected QT and JT, and men in the lowest category of T4 appeared to have shorter corrected QT and JT.
  
  
  CONCLUSIONS
  Variation in thyroid hormone levels in the general population, even within the normal range, was associated with various ECG changes.
authors.affiliation: Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA.
authors.forename: Yiyi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Wendy S
authors.initials: WS
authors.lastname: Post
authors.forename: Alan
authors.initials: A
authors.lastname: Cheng
authors.forename: Elena
authors.initials: E
authors.lastname: Blasco-Colmenares
authors.forename: Gordon F
authors.initials: GF
authors.lastname: Tomaselli
authors.forename: Eliseo
authors.initials: E
authors.lastname: Guallar
mesh_terms: D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
chemical_list: D013963:Thyroid Hormones; D013972:Thyrotropin; D013974:Thyroxine