Unreliability of the %VO2 reserve versus %heart rate reserve relationship for aerobic effort relative intensity assessment in chronic heart failure patients on or off beta-blocking therapy

Abstract

Percentage of heart rate reserve (%HRR) has been shown to be equivalent to percentage of VO2 reserve (%VO2R) in normal individuals, but it is not clear whether this is also true for chronic heart failure (CHF) patients. Design This study aimed to evaluate the reliability of the %VO2R versus %HRR relationship for aerobic effort relative intensity assessment in CHF patients. We studied 388 patients with CHF, of whom 213 were on carvedilol (CHF on βb) and 175 were off the drug (CHF off βb), and 40 normal individuals (N). %VO 2R and %HRR values were evaluated at matched steps during cardiopulmonary exercise testing. The %VO 2R versus %HRR regression was determined for each group (CHF, CHF on βb, CHF off βb, N) as a whole and as the mean of individual regressions. %VO 2R strongly correlated with %HRR in both N and CHF, at both group and mean individual regressions, with slope and y-intercept values significantly lower and higher, respectively, in CHF than N. The 95% prediction interval of %VO 2R for a given %HRR value was 24% points in N but rose to 41 in CHF, and the mean regression line coincided with identity line in N but not in CHF. These results were independent of beta-blockade. In CHF patients the %VO 2R versus %HRR relationship is unreliable for assessment of aerobic effort relative intensity, because of a large prediction interval of %VO 2R and lack of coincidence with the identity line, independently of beta-blocking therapy. This implies that the %VO 2R versus %HRR relationship should be determined directly in each patient. © 2007, European Society of Cardiology. All rights reserved.