title: Exercise capacity at submaximal heart rate and prognosis.
abstract: BACKGROUND
  Submaximal exercise testing can be useful for individuals with limitations to performing maximal exercise. Recent studies suggested that a low workload at a heart rate 100 beats/minute (HR(100)) was associated with a greater risk of cardiovascular (CV) mortality than maximal exercise capacity. This study evaluated the prognostic value of METs achieved at HR(100) (METs(100)) in patients referred for treadmill testing.
  
  
  METHODS
  We studied 1446 patients (56+/-12 years; 76 females) without heart failure or beta-blockers treatment (1997-2004).
  
  
  RESULTS
  During a period of 7.0+/-2.3 years, 35 (2.5%) patients died from CV causes. Compared to survivors, the non-survivors were older (69+/-9 vs. 56+/-12 years, p<0.001); had a higher prevalence of diabetes (27% vs. 14%, p=0.04), coronary artery disease (57% vs. 25%, p<0.05) and stroke (9% vs. 2%, p<0.001). Non-survivors had lower Duke Treadmill Scores (DTS) (2.8+/-6.8 vs. 9.7+/-5.5; p<0.001) and exercise capacity (7.5+/-3.3 vs.11.0+/-3.8 METs, p<0.001). At HR(100), METs (median (range): 3.8 (2.8-4.0) vs. 3.5 (3.3-3.5)) and %HR reserve achieved (45+/-13% vs. 34+/-17%; p<0.001) were higher in non-survivors. In Cox model, age-adjusted METs(100) was not a significant predictor of CV mortality. In contrast, each one MET increase in exercise capacity was associated with a 17% increase in survival (HR=0.83, 95% CI 0.73-0.93, p=0.002). DTS was also a significant predictor of CV mortality.
  
  
  CONCLUSIONS
  In our population, METs at HR(100) was not a significant predictor of CV mortality.
authors.affiliation: Stanford University Medical Center-Division of Cardiovascular Medicine, Palo Alto, CA, United States. vyvanle@gmail.com
authors.forename: Vy-Van
authors.initials: VV
authors.lastname: Le
authors.forename: Teferi
authors.initials: T
authors.lastname: Mitiku
authors.forename: David
authors.initials: D
authors.lastname: Hadley
authors.forename: Jonathan
authors.initials: J
authors.lastname: Myers
authors.forename: Victor
authors.initials: V
authors.lastname: Froelicher
mesh_terms: D000328:Adult; D000368:Aged; D001919:Bradycardia / Q000175:diagnosis / Q000401:mortality / Q000503:physiopathology; D002318:Cardiovascular Diseases / Q000175:diagnosis* / Q000401:mortality* / Q000503:physiopathology; D015331:Cohort Studies; D004562:Electrocardiography / Q000379:methods; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012189:Retrospective Studies