title: Heart rate variability measured early in patients with evolving acute coronary syndrome and 1-year outcomes of rehospitalization and mortality.
abstract: OBJECTIVE
  This study sought to examine the prognostic value of heart rate variability (HRV) measurement initiated immediately after emergency department presentation for patients with acute coronary syndrome (ACS).
  
  
  BACKGROUND
  Altered HRV has been associated with adverse outcomes in heart disease, but the value of HRV measured during the earliest phases of ACS related to risk of 1-year rehospitalization and death has not been established.
  
  
  METHODS
  Twenty-four-hour Holter recordings of 279 patients with ACS were initiated within 45 minutes of emergency department arrival; recordings with ≥18 hours of sinus rhythm were selected for HRV analysis (number [N] =193). Time domain, frequency domain, and nonlinear HRV were examined. Survival analysis was performed.
  
  
  RESULTS
  During the 1-year follow-up, 94 patients were event-free, 82 were readmitted, and 17 died. HRV was altered in relation to outcomes. Predictors of rehospitalization included increased normalized high frequency power, decreased normalized low frequency power, and decreased low/high frequency ratio. Normalized high frequency >42 ms(2) predicted rehospitalization while controlling for clinical variables (hazard ratio [HR] =2.3; 95% confidence interval [CI] =1.4-3.8, P=0.001). Variables significantly associated with death included natural logs of total power and ultra low frequency power. A model with ultra low frequency power <8 ms(2) (HR =3.8; 95% CI =1.5-10.1; P=0.007) and troponin >0.3 ng/mL (HR =4.0; 95% CI =1.3-12.1; P=0.016) revealed that each contributed independently in predicting mortality. Nonlinear HRV variables were significant predictors of both outcomes.
  
  
  CONCLUSIONS
  HRV measured close to the ACS onset may assist in risk stratification. HRV cut-points may provide additional, incremental prognostic information to established assessment guidelines, and may be worthy of additional study.
authors.affiliation: Electrocardiographic Monitoring Research Laboratory, School of Nursing, Department of Physiological Nursing, University of California, San Francisco, CA, USA.
authors.forename: Patricia R E
authors.initials: PR
authors.lastname: Harris
authors.affiliation: Heart Rate Variability Laboratory, School of Medicine, Division of Cardiology, Washington University, St Louis, MO, USA.
authors.forename: Phyllis K
authors.initials: PK
authors.lastname: Stein
authors.affiliation: Cardiology Services, Mount Zion, Department of Medicine, Division of Cardiology, University of California, San Francisco, CA, USA.
authors.forename: Gordon L
authors.initials: GL
authors.lastname: Fung
authors.affiliation: School of Nursing, Department of Physiological Nursing, Division of Cardiology, University of California, San Francisco, CA, USA.
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Drew
mesh_terms: D054058:Acute Coronary Syndrome / Q000175:diagnosis* / Q000401:mortality* / Q000503:physiopathology / Q000628:therapy; D000368:Aged; D000369:Aged, 80 and over; D016009:Chi-Square Distribution; D018572:Disease-Free Survival; D015716:Electrocardiography, Ambulatory; D004636:Emergency Service, Hospital; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D017711:Nonlinear Dynamics; D010359:Patient Readmission; D011237:Predictive Value of Tests; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors
keywords: autonomic cardiac function; coronary artery disease; hospital readmittance; mortality; outcomes research; risk assessment