title: Genetic influences on resting electrocardiographic variables in older women: a twin study.
abstract: BACKGROUND
  Previous studies in young and middle-aged men and women have shown that resting electrocardiographic (ECG) variables are influenced by genetic factors. However, the extent to which resting ECG variables are influenced by genetic factors in older women is unknown. Thus, the aim of this study was to estimate the relative contribution of genetic and environmental influences to individual differences in resting ECG variables among older female twins without overt cardiac diseases.
  
  
  METHODS
  Resting ECG recordings were obtained from 186 monozygotic and 203 dizygotic twin individuals, aged 63-76 years. Quantitative genetic modeling was used to decompose the phenotypic variance in each resting ECG variable into additive genetic, dominance genetic, shared environmental, and unique environmental influences.
  
  
  RESULTS
  The results showed that individual differences in the majority of the resting ECG variables were moderately to highly explained by additive genetic influences, ranging from 32% for T axis to 72% for TV(5). The results also suggested dominance genetic influences on QRS duration, TV(1), and Sokolow-Lyon voltage (36%, 53%, and 57%, respectively). Unique environmental influences were important for each resting ECG variable, whereas shared environmental influences were detected only for QT interval and QTc.
  
  
  CONCLUSIONS
  In older women without overt cardiac diseases, genetic influences explain a moderate to high proportion of individual differences in the majority of the resting ECG variables. Genetic influences are especially strong for T-wave amplitudes, left ventricular mass, and hypertrophy indices, whereas other variables, including heart rate, intervals, and axes, are more affected by environmental influences.
authors.affiliation: Department of Health Sciences, University of Jyväskylä, Finland. sara.mutikainen@gmail.com
authors.forename: Sara
authors.initials: S
authors.lastname: Mutikainen
authors.forename: Alfredo
authors.initials: A
authors.lastname: Ortega-Alonso
authors.forename: Markku
authors.initials: M
authors.lastname: Alén
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.forename: Jouko
authors.initials: J
authors.lastname: Karjalainen
authors.forename: Taina
authors.initials: T
authors.lastname: Rantanen
authors.forename: Urho M
authors.initials: UM
authors.lastname: Kujala
mesh_terms: D000368:Aged; D000375:Aging / Q000235:genetics*; D015331:Cohort Studies; D016001:Confidence Intervals; D004562:Electrocardiography; D005260:Female; D005387:Finland; D020022:Genetic Predisposition to Disease; D006339:Heart Rate / Q000235:genetics*; D006801:Humans; D008875:Middle Aged; D012016:Reference Values; D012146:Rest; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic