title: Reduced heart rate variability: an indicator of cardiac uncoupling and diminished physiologic reserve in 1,425 trauma patients.
abstract: BACKGROUND
  Measurements of a patient's physiologic reserve (age, injury severity, admission lactic acidosis, transfusion requirements, and coagulopathy) reflect robustness of response to surgical insult. We have previously shown that cardiac uncoupling (reduced heart rate variability, HRV) in the first 24 hours after injury correlates with mortality and autonomic nervous system failure. We hypothesized: Deteriorating physiologic reserve correlates with reduced HRV and cardiac uncoupling.
  
  
  METHODS
  There were 1,425 trauma ICU patients that satisfied the inclusion criteria. Differences in mortality across categorical measurements of the domains of physiologic reserve were assessed using the chi test. The relationship of cardiac uncoupling and physiologic reserve was examined using multivariate logistic regression models for various levels of cardiac uncoupling (>0 through 28% reduced HRV in the first 24 hours).
  
  
  RESULTS
  Of these, 797 (55.9%) patients exhibited cardiac uncoupling. Deteriorating measures of physiologic reserve reflected increased risk of death. Measures of acidosis (admission lactate, time to lactate normalization, and lactate deterioration over the first 24 hours), coagulopathy, age, and injury severity contributed significantly to the risk of cardiac uncoupling (area under receiver operator curve, ROC=0.73). The association between deteriorating reserve and cardiac uncoupling increases with the threshold for uncoupling (ROC=0.78).
  
  
  CONCLUSIONS
  Reduced heart rate variability is a new biomarker reflecting the loss of command and control of the heart (cardiac uncoupling). Risk of cardiac uncoupling increases significantly as a patient's physiologic reserve deteriorates and physiologic exhaustion approaches. Cardiac uncoupling provides a noninvasive, overall measure of a patient's clinical trajectory over the first 24 hours of ICU stay.
authors.affiliation: Department of Surgical Sciences, Vanderbilt University Medical Center, Nashville, Tennessee 37212, USA. john.morris@vanderbilt.edu
authors.forename: John A
authors.initials: JA
authors.lastname: Morris
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Norris
authors.forename: Asli
authors.initials: A
authors.lastname: Ozdas
authors.forename: Lemuel R
authors.initials: LR
authors.lastname: Waitman
authors.forename: Frank E
authors.initials: FE
authors.lastname: Harrell
authors.forename: Anna E
authors.initials: AE
authors.lastname: Williams
authors.forename: Hanqing
authors.initials: H
authors.lastname: Cao
authors.forename: Judith M
authors.initials: JM
authors.lastname: Jenkins
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001341:Autonomic Nervous System / Q000503:physiopathology; D005260:Female; D006339:Heart Rate; D006801:Humans; D015601:Injury Severity Score; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D015999:Multivariate Analysis; D011379:Prognosis; D012306:Risk; D014947:Wounds and Injuries / Q000150:complications / Q000503:physiopathology*