title: Chronotropic and neurohumoral markers for the evaluation of functional capacity in patients with impaired left ventricular function.
abstract: BACKGROUND
  Brain natriuretic peptide (BNP) levels correlate with functional capacity in patients with heart failure. Autonomic dysfunction and baro-chemo reflex balance play a role in conditioning exercise tolerance and chronotropic competence in heart failure. In this study we examined the relationship between N-terminal pro-brain natriuretic peptide (NT-pro-BNP) and heart rate (HR) response during cardiopulmonary exercise testing and the ability of those two markers to detect low functional class patients.
  
  
  METHODS
  We studied 100 patients (age 59 +/- 13 yrs) with heart failure and left ventricular ejection fraction 35 +/- 9% who underwent treadmill cardiopulmonary exercise testing using the Dargie protocol. HR response was assessed by the chronotropic response index (CRI), which is calculated using the formula CRI = (peak HR - rest HR) /(220 - age - rest HR) x 100 (%). Blood samples for NT-pro-BNP assessment were taken before exercise.
  
  
  RESULTS
  The overall peak VO2 achieved was 18 +/- 5 ml/kg/mm and CRI was 70 +/- 26% (normal value >80%). CRI correlated both with peak VO2 (r = 0.50, p < 0.001) and VE/VCO2 (r = -0.24, p < 0.05). Peak VO2 correlated strongly with NT-pro-BNP (r = -0.77, p < 0.001). NT-pro-BNP values >335 pg/ml showed 83% sensitivity and 76% specificity for detecting peak VO2 values <20 ml/kg/mm (AUC=86%, p < 0.001). CRI values >79% showed 70% sensitivity and 60% specificity for detecting peak VO2 values <20 ml/kg/mm (AUC=72%, p < 0.001). CRI correlated well with NT-pro-BNP at rest (r = -0.31, p < 0.001).
  
  
  CONCLUSIONS
  In patients with heart failure, CR1 correlates significantly with both functional capacity derived from cardiopulmonary exercise testing and NT-pro-BNP levels. These findings may support the use of CR1 as a simple noninvasive marker of heart failure severity.
authors: 1st Cardiology Department, Onassis Cardiac Surgery Center, Athens, Greece. mankal1@otenet.gr
authors: Manolis S
authors: MS
authors: Kallistratos
authors: Athanlaslos
authors: A
authors: Dritsas
authors: Ioannis D
authors: ID
authors: Laoutaris
authors: Dennis V
authors: DV
authors: Cokkinos
mesh_terms: D000368:Aged; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D020097:Natriuretic Peptide, Brain / Q000097:blood*; D010101:Oxygen Consumption; D010446:Peptide Fragments / Q000097:blood*; D011446:Prospective Studies; D012372:ROC Curve; D013318:Stroke Volume; D018487:Ventricular Dysfunction, Left / Q000097:blood / Q000503:physiopathology*
chemical_list: D010446:Peptide Fragments; C109794:pro-brain natriuretic peptide (1-76); D020097:Natriuretic Peptide, Brain