title: Prediction of cardiovascular death using a novel heart rate recovery parameter.
abstract: BACKGROUND
  Reassertion of vagal tone after exercise is an important component in mediating heart rate recovery (HRR), and both vagal tone and HRR have been associated with mortality. HRR is strongly related to the increase in HR from resting to peak exercise. We hypothesized that a score normalized for HR increase would better isolate the vagal influences in recovery from the sympathetic influences supporting maximal exercise.
  
  
  METHODS
  HRR data from 1959 veterans were analyzed. During a mean follow-up of 5.3 years, 187 (9.5%) subjects died-70 (37%) due to cardiovascular (CV) causes. A method was developed to compare HRR curve shapes normalized for differences in HR increase. Differences in the slopes of the normalized curves over the range 50-70 s were observed between the survivors and nonsurvivors, and a prognostic measurement, HRRS50-70, was developed. The incremental increases in predictive power and discriminative accuracy provided by Duke Treadmill Score (DTS), clinical parameters, HR increase, recovery variables, and HRRS50-70 were assessed.
  
  
  RESULTS
  In the age-adjusted Cox analysis, the only significant exercise indices associated with CV mortality were HR increase (P < 0.0001), HRRS50-70 (P = 0.01), and DTS (P < 0.001). The increased risk for patients in the lowest tertile for all three indices, relative to those with normal scores, was 22 (95% CI, 7.9-63; P < 0.0001).
  
  
  CONCLUSIONS
  HRRS50-70 is independent of and complementary to HR increase and DTS. Patients with abnormal HRRS50-70 and abnormal DTS and/or HR increase are at substantially increased risk of CV mortality.
authors.affiliation: Cardiac Science, Bothell, WA, USA. dave_hadley@comcast.net
authors.forename: David M
authors.initials: DM
authors.lastname: Hadley
authors.forename: Frederick E
authors.initials: FE
authors.lastname: Dewey
authors.forename: James V
authors.initials: JV
authors.lastname: Freeman
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Myers
authors.forename: Victor F
authors.initials: VF
authors.lastname: Froelicher
mesh_terms: D000368:Aged; D002318:Cardiovascular Diseases; D005080:Exercise Test; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011237:Predictive Value of Tests; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012307:Risk Factors; D014728:Veterans