Contribution of peak respiratory exchange ratio to peak VO2 prognostic reliability in patients with chronic heart failure and severely reduced exercise capacity

Background We evaluated the influence of peak respiratory exchange ratio (pRER), as an index of effort adequacy, on peak VO2 prognostic reliability in patients with chronic heart failure (CHF) and reduced exercise capacity, whose peak VO2 may be underestimated because of poor patient motivation. Methods A cardiopulmonary exercise test was performed in 570 patients with CHF (age 60 +/- 10 years, ejection fraction 26% +/- 7%, New York Heart Association class 2.2 +/- 0.6), 193 of whom had a peak VO2 that was >10 but greater than or equal to14 mL/kg/min (reduced exercise capacity) and 80 of whom had a peak VO2 less than or equal to10 mL/kg/min (severely reduced exercise capacity). Results Seventy-eight events (72 cardiovascular deaths and 6 status I heart transplantations) occurred during follow-up (19.6 +/- 14 months). The 2-year survival rate was 69% in patients with a peak VO2 less than or equal to10 and 83% in patients with a peak VO2 > 10 but less than or equal to14 (P < .0001). However, in the group of patients with a peak VO2 ≤10, patients who had a pRER ≥1.15 had a 2-year survival rate of 52%, and this pRER value (but not ≥1, ≥1.05, or ≥1.10) was the only independent predictor of the composite end point (χ(2) = 4.73, P = .03). Conversely, in the group of patients with a peak VO2 ≤10, patients who had a pRER value < 1.15 had a survival rate of 83%, which was comparable with that of the group of patients with a peak VO2 >10 but less than or equal to14. Conclusion Patients with CHF and severely reduced exercise capacity should be encouraged to exercise to an RER as close as possible to 1.15, to ascertain their motivation and ensure their peak VO2 prognostic reliability.