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

BACKGROUND: 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. METHODS: 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). %VO2R and %HRR values were evaluated at matched steps during cardiopulmonary exercise testing. The %VO2R 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. RESULTS: %VO2R 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 %VO2R 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. CONCLUSIONS: In CHF patients the %VO2R versus %HRR relationship is unreliable for assessment of aerobic effort relative intensity, because of a large prediction interval of %VO2R and lack of coincidence with the identity line, independently of beta-blocking therapy. This implies that the %VO2R versus %HRR relationship should be determined directly in each patient.