PERCENT HEART RATE RESERVE IS EQUIVALENT TO PERCENT VO2 RESERVE IN PATIENTS WITH HEART FAILURE

Abstract

Previous studies show that % heart rate reserve (HRR) is equivalent to % VO2 reserve (VO2R) in healthy subjects (Swain, et al.) and those with prior myocardial infarction (Brawner, et al.). This study tested the hypothesis that % HRR is equivalent to % VO2R in patients with heart failure (HF) due to left ventricular systolic dysfunction. We queried the Henry Ford PREventive Cardiology Outcomes (PRECO) database for patients with HF, ejection fraction ≤ 35%, sinus rhythm and an inaugural, symptom-limited graded treadmill test with gas exchange performed between 8/1/1998 and 7/31/2000. Seventy-two patients were identified (46 males, 26 females; age = 53 ± 12 yr; EF = 22 ± 8%; VO2 = 16.5 ± 4 mL/kg/min; mean ± SD). Heart rate and VO2 data were collected continuously and averaged in 15s intervals. Linear regression was used to analyze the relationship of % HRR to % VO2R and % HRR to % VO2max. A mean slope and y-intercept was calculated for each regression line. T-tests were used to determine if either line was significantly different from a line of identity (slope = 1, y-intercept = 0) and if the two lines differed from each other. A sub-analysis examined the effect of beta-adrenergic blockade (BB) therapy on these relationships. Results: The mean slope and y-intercept for % HRR vs % VO2R was 0.97 ± 0.02 (mean ± SE) and −0.06 ± 0.02, respectively; not different from a line of identity. The relationship of % HRR vs % VO2max was significantly different from a line of identity (p ≤ 0.001), with a mean slope and y-intercept of 1.25 ± 0.03 and −0.34 ± 0.03, respectively. Seperate analyses for BB therapy did not change these results. Conclusion: Independent of BB therapy, in patients with HF due to left ventricular systolic dysfunction, exercise intensity should be based on % VO2R, not % VO2max.