title: Respiratory sinus arrhythmia as a predictor of sudden cardiac death after myocardial infarction.
abstract: BACKGROUND
  Measurement of high-frequency (HF) spectral power of heart rate (HR) variability has not been able to identify the patients at risk of sudden cardiac death (SCD) despite the experimental evidence of protective role of vagal activity for fatal arrhythmias.
  
  
  OBJECTIVE
  We developed a novel respiratory sinus arrhythmia (RSA) analysis method and tested its ability to predict SCD after an acute myocardial infarction.
  
  
  METHODS
  The RSA analysis method was developed in 13 subjects from simultaneous recordings of respiration and R-R intervals. An adaptive threshold was computed based on the zero-phase forward and reverse digital filtering in the analysis of RSA. With this method, only respiration-related R-R interval fluctuations are included. The prognostic power of RSA, analyzed from 24-hour electrocardiographic recordings, was subsequently assessed in a large postinfarction population including 1631 patients with mean follow-up of 40 +/- 17 months.
  
  
  RESULTS
  Depressed RSA was a strong predictor of SCD (hazard ratio 7.4; 95% CI 3.6-15.1; P 0.0001) but only a weak predictor of non-SCD. The RSA index remained an independent predictor of SCD after adjustments for ejection fraction and other clinical risk variables (RR 4.7; 95% CI 2.28-9.85).
  
  
  CONCLUSIONS
  Reduced respiratory-related HR dynamics, detected by RSA index, are a specific marker of an increased risk of SCD among postinfarction patients.
authors.affiliation: University of Oulu, Department of Internal Medicine, Division of Cardiology, Oulu, Finland.
authors.forename: Mirja
authors.initials: M
authors.lastname: Peltola
authors.forename: Mikko P
authors.initials: MP
authors.lastname: Tulppo
authors.forename: Antti
authors.initials: A
authors.lastname: Kiviniemi
authors.forename: Arto J
authors.initials: AJ
authors.lastname: Hautala
authors.forename: Tapio
authors.initials: T
authors.lastname: Seppänen
authors.forename: Petra
authors.initials: P
authors.lastname: Barthel
authors.forename: Axel
authors.initials: A
authors.lastname: Bauer
authors.forename: Georg
authors.initials: G
authors.lastname: Schmidt
authors.forename: Heikki V
authors.initials: HV
authors.lastname: Huikuri
authors.forename: Timo H
authors.initials: TH
authors.lastname: Mäkikallio
mesh_terms: D000368:Aged; D000465:Algorithms; D001146:Arrhythmia, Sinus / Q000175:diagnosis*; D016757:Death, Sudden, Cardiac / Q000453:epidemiology* / Q000209:etiology; D003936:Diagnosis, Computer-Assisted / Q000379:methods; D015716:Electrocardiography, Ambulatory / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000150:complications* / Q000503:physiopathology; D011237:Predictive Value of Tests; D011379:Prognosis; D016016:Proportional Hazards Models; D015656:Respiratory Mechanics; D012307:Risk Factors; D012680:Sensitivity and Specificity