Background: Comparing the prognostic value of peak oxygen uptake (VO2max) in absolute values and percentage of predicted VO2max (%PredVO2) in terms of prognostic stratification, contradictory references are found in the medical literature. In theory, the measurement of VO2max relative to a normal subject should improve its predictive capacity, because VO2max is influenced by gender, weight, physical activity and age.
Objectives: To compare the prognostic value of VO2max and %PredVO2 (Jones equation) in an adult population (> or = 20 years) of patients with left ventricular systolic dysfunction and to study the influence of age on these parameters.
Population and methods: We review data from the first cardiopulmonary stress test performed in 295 consecutive patients with left ventricular systolic dysfunction (ejection fraction < or = 40%); mean age was 52 +/- 10 years, 81% were male, and 76 aged > or = 60 years. In 52%, the etiology was ischemic. We evaluated demographic and clinical variables, the baseline ECG and the medication used before the test. We compared VO2max (ml/kg/min) and %PredVO2 in terms of prognostic stratification for the combined endpoint (death and/or heart transplant) for 2 years of follow-up.
Results: We detected 60 patients with events (42 deaths and 18 transplants). ROC curve analysis was used to determine the best cut-off value for VO2max and %PredVO2 to identify patients with events. The best cut-off for VO2max was < or = 19 ml/kg/min and < or = 49% for %PredVO2 in the total population, and in the event-free survival analysis, by log-rank test, we obtained p < 0.001 for both cut-offs. Considering the two extreme age groups (20-40 years and > or = 60 years), we found different cut-off values. In the youngest group we obtained VO2max of < or = 23 ml/kg/min and %PredVO2 of < or = 59%, and in the elderly < or = 12.5 ml/kg/min and < or = 64% respectively. For the intermediate group, the cut-off values were the same as for the total population. In the youngest patients, the new cut-offs did not offer an improvement in accuracy. In the elderly, for VO2max, we obtained an improvement in specificity from 28 to 86% and a reduction in sensitivity from 95 to 50%, with an improvement in accuracy from 46.8 to 75.9% (p = 0.05). With regard to %PredVO2, specificity fell from 86 to 61% and sensitivity increased from 50 to 82%, with similar accuracy (75.9 to 67%, p = 0.78).
Conclusions: In the extreme age groups, we obtained different cut-off values, but only for the elderly (VO2max < or = 12.5 ml/kg/min and %PredVO2 < or = 64%). A benefit in terms of accuracy was only obtained in respect of VO2max, because for %PredVO2, there is already a correction for age through the Jones equation.