title: Clinical and demographic determinants of heart rate variability in patients post myocardial infarction: insights from the cardiac arrhythmia suppression trial (CAST).
abstract: BACKGROUND
  Clinical and demographic determinants of heart rate variability (HRV), an almost universal predictor of increased mortality, have not been systematically investigated in patients post myocardial infarction (MI).
  
  
  OBJECTIVE
  The study was undertaken to evaluate the relationship between pretreatment clinical and demographic variables and HRV in the Cardiac Arrhythmia Suppression Trial (CAST).
  
  
  METHODS
  CAST patients were post MI and had > or =6 ventricular premature complexes/h on pretreatment recording. Patients in this substudy (n = 769) had usable pretreatment and suppression tapes and were successfully randomized on the first antiarrhythmic treatment. Tapes were rescanned; only time domain HRV was reported because many tapes lacked the calibrated timing signal needed for accurate frequency domain analysis. Independent predictors of HRV were determined by stepwise selection.
  
  
  RESULTS
  Coronary artery bypass graft surgery (CABG) after the qualifying MI was the strongest determinant of HRV. The markedly decreased HRV associated with CABG was not associated with increased mortality. Ejection fraction and diabetes were also independent predictors of HRV. Other predictors for some indices of HRV included beta-blocker use, gender, time from MI to Holter, history of CABG before the qualifying MI, and systolic blood pressure. Decreased HRV did not predict mortality for the entire group. For patients without CABG or diabetes, decreased standard deviation of all NN intervals (SDANN) predicted mortality. Clinical and demographic factors accounted for 31% of the variance in the average of normal-to-normal intervals (AVGNN) and 13-26% of the variance in other HRV indices.
  
  
  CONCLUSIONS
  Heart rate variability post MI is largely independent of clinical and demographic factors. Antecedent CABG dramatically reduces HRV. Recognition of this is necessary to prevent misclassification of risk in patients post infarct.
authors.affiliation: Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA.
authors.forename: P K
authors.initials: PK
authors.lastname: Stein
authors.forename: P P
authors.initials: PP
authors.lastname: Domitrovich
authors.forename: R E
authors.initials: RE
authors.lastname: Kleiger
authors.forename: K B
authors.initials: KB
authors.lastname: Schechtman
authors.forename: J N
authors.initials: JN
authors.lastname: Rottman
mesh_terms: D000368:Aged; D000889:Anti-Arrhythmia Agents / Q000627:therapeutic use; D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000517:prevention & control; D001026:Coronary Artery Bypass; D003925:Diabetic Angiopathies / Q000503:physiopathology; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000150:complications / Q000401:mortality / Q000503:physiopathology* / Q000601:surgery; D011237:Predictive Value of Tests; D013318:Stroke Volume; D016019:Survival Analysis
chemical_list: D000889:Anti-Arrhythmia Agents