title: Frequency domain measures of heart period variability to assess risk late after myocardial infarction.
abstract: OBJECTIVE
  To determine whether spectral measures of heart period (RR) variability predict death when measured late after infarction, we studied patients in the Cardiac Arrhythmia Pilot Study (CAPS) who survived for 1 year and had a 24-h electrocardiographic (ECG) recording made after the CAPS drug was washed out.
  
  
  BACKGROUND
  Four components of the heart period power spectrum--ultra low frequency (< 0.0033 Hz), very low frequency (0.0033 to < 0.04 Hz), low frequency (0.04 to < 0.15 Hz) and high frequency power (0.15 to < 0.40 Hz)--plus total power (1.157 x 10(-5) to < 0.40 Hz) and the ratio of low to high frequency power predict mortality when measured < 30 days after myocardial infarction. However, these variables increase to steady state values by 3 months after infarction and the prognostic significance of recovery values is unknown.
  
  
  METHODS
  The 24-h power spectral density was computed from ECG recordings made 1 year after infarction using fast Fourier transforms and the six measures listed were calculated. The values were dichotomized at cut points that maximized the association with mortality.
  
  
  RESULTS
  Each measure of RR variability had a strong and significant univariate association with mortality; the relative risks for these variables ranged from 2.5 to 5.6. After adjustment for age, New York Heart Association functional class, rales in the coronary care unit, left ventricular ejection fraction and ventricular arrhythmias, some measures of heart period variability still had a strong and significant independent association with all-cause mortality.
  
  
  CONCLUSIONS
  Spectral measures of heart period variability, measured late after infarction, predict death.
authors.affiliation: Department of Medicine, School of Public Health, Columbia University, New York, New York.
authors.forename: J T
authors.initials: JT
authors.lastname: Bigger
authors.forename: J L
authors.initials: JL
authors.lastname: Fleiss
authors.forename: L M
authors.initials: LM
authors.lastname: Rolnitzky
authors.forename: R C
authors.initials: RC
authors.lastname: Steinman
mesh_terms: D015716:Electrocardiography, Ambulatory / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000175:diagnosis / Q000401:mortality* / Q000503:physiopathology; D011237:Predictive Value of Tests; D011379:Prognosis; D012307:Risk Factors; D012815:Signal Processing, Computer-Assisted; D016019:Survival Analysis; D013997:Time Factors