title: Heart rate variability in bipolar disorder: A systematic review and meta-analysis.
abstract: Heart rate variability (HRV) has been suggested reduced in bipolar disorder (BD) compared with healthy individuals (HC). This meta-analysis investigated: HRV differences in BD compared with HC, major depressive disorder or schizophrenia; HRV differences between affective states; HRV changes from mania/depression to euthymia; and HRV changes following interventions.
  
  
  
  A systematic review and meta-analysis reported according to the PRISMA guidelines was conducted. MEDLINE, Embase, PsycINFO, The Cochrane Library and Scopus were searched. A total of 15 articles comprising 2534 individuals were included.
  
  
  
  HRV was reduced in BD compared to HC (g=-1.77, 95% CI: -2.46; -1.09, P<0.001, 10 comparisons, n=1581). More recent publication year, larger study and higher study quality were associated with a smaller difference in HRV. Large between-study heterogeneity, low study quality, and lack of consideration of confounding factors in individual studies were observed.
  
  
  
  This first meta-analysis of HRV in BD suggests that HRV is reduced in BD compared to HC. Heterogeneity and methodological issues limit the evidence. Future studies employing strict methodology are warranted.
authors.affiliation: Psychiatric Center Copenhagen, Rigshospitalet, University of Copenhgaen, Blegdamsvej 9, DK- 2100 Copenhagen, Denmark. Electronic address: maria@faurholt-jepsen.dk.
authors.forename: Maria
authors.initials: M
authors.lastname: Faurholt-Jepsen
authors.affiliation: Psychiatric Center Copenhagen, Rigshospitalet, University of Copenhgaen, Blegdamsvej 9, DK- 2100 Copenhagen, Denmark.
authors.forename: Lars Vedel
authors.initials: LV
authors.lastname: Kessing
authors.affiliation: Psychiatric Center Copenhagen, Rigshospitalet, University of Copenhgaen, Blegdamsvej 9, DK- 2100 Copenhagen, Denmark.
authors.forename: Klaus
authors.initials: K
authors.lastname: Munkholm
mesh_terms: D001714:Bipolar Disorder; D003865:Major Depressive Disorder; D006339:Heart Rate; D006801:Humans; D012559:Schizophrenia
keywords: Bipolar disorder; HRV; Heart rate variability; Meta-analysis; Systematic review