title: Major depressive disorder with melancholia displays robust alterations in resting state heart rate and its variability: implications for future morbidity and mortality.
abstract: BACKGROUND
  Major depressive disorder (MDD) is associated with increased heart rate and reductions in its variability (heart rate variability, HRV) - markers of future morbidity and mortality - yet prior studies have reported contradictory effects. We hypothesized that increases in heart rate and reductions in HRV would be more robust in melancholia relative to controls, than in patients with non-melancholia.
  
  
  METHODS
  A total of 72 patients with a primary diagnosis of MDD (age M: 36.26, SE: 1.34; 42 females) and 94 controls (age M: 35.69, SE: 1.16; 52 females) were included in this study. Heart rate and measures of its variability (HRV) were calculated from two 2-min electrocardiogram recordings during resting state. Propensity score matching controlled imbalance on potential confounds between patients with melancholia (n = 40) and non-melancholia (n = 32) including age, gender, disorder severity, and comorbid anxiety disorders.
  
  
  RESULTS
  MDD patients with melancholia displayed significantly increased heart rate and lower resting-state HRV (including the square root of the mean squared differences between successive N-N intervals, the absolute power of high frequency and standard deviation of the Poincaré plot perpendicular to the line of identity measures of HRV) relative to controls, findings associated with a moderate effect size (Cohens d's = 0.56-0.58). Patients with melancholia also displayed an increased heart rate relative to those with non-melancholia (Cohen's d = 0.20).
  
  
  CONCLUSIONS
  MDD patients with melancholia - but not non-melancholia - display robust increases in heart rate and decreases in HRV. These findings may underpin a variety of behavioral impairments in patients with melancholia including somatic symptoms, cognitive impairment, reduced responsiveness to the environment, and over the longer-term, morbidity and mortality.
authors.affiliation: Discipline of Psychiatry, Sydney Medical School, University of Sydney Sydney, NSW, Australia ; School of Psychology, Faculty of Science, University of Sydney Sydney, NSW, Australia ; Centro de Pesquisa Clínica e Epidemiológica, Hospital Universitário - Universidade de São Paulo São Paulo, Brazil.
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Kemp
authors.affiliation: School of Psychology, Faculty of Science, University of Sydney Sydney, NSW, Australia ; NORMENT, K.G. Jebsen Centre for Psychosis Research, Institute of Clinical Medicine, University of Oslo Oslo, Norway ; Division of Mental Health and Addiction, Oslo University Hospital Oslo, Norway.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Quintana
authors.affiliation: Discipline of Psychiatry, Sydney Medical School, University of Sydney Sydney, NSW, Australia.
authors.forename: Candice R
authors.initials: CR
authors.lastname: Quinn
authors.affiliation: Discipline of Psychiatry, Sydney Medical School, University of Sydney Sydney, NSW, Australia.
authors.forename: Patrick
authors.initials: P
authors.lastname: Hopkinson
authors.affiliation: Discipline of Psychiatry, Sydney Medical School, University of Sydney Sydney, NSW, Australia ; Brain Dynamics Centre, Westmead Millennium Institute, University of Sydney - Westmead Hospital Sydney, NSW, Australia.
authors.forename: Anthony W F
authors.initials: AW
authors.lastname: Harris
keywords: ECG; HRV; electrocardiogram; heart rate; heart rate variability; melancholia; non-melancholia; resting state