Prognostic impact of peak oxygen uptake and percentage of predicted value of peak oxygen uptake in patients with left ventricular dysfunction.

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.

Recovery kinetics of oxygen uptake after cardiopulmonary exercise test and prognosis in patients with left ventricular dysfunction.

INTRODUCTION: The prognostic value of peak oxygen uptake (peak VO2) in patients with left ventricular systolic dysfunction is currently recognized and accepted. Some studies have shown that other cardiopulmonary exercise test (CPET) parameters have additional value. OBJECTIVES: To evaluate whether our population of patients with left ventricular dysfunction had similar results to those found by other investigators who showed that a slow normalization of oxygen uptake (VO2) during the recovery period of a CPET has prognostic value, and whether the recovery phase parameters have additional prognostic value to peak VO2 in these patients. METHODS: We studied 292 consecutive adult patients (81.5% male; mean age 52.4 +/- 10.6 years) with an ejection fraction below 40% (mean 23.6 +/- 8.8%) given their first symptom-limited CPET between 03/1993 and 08/2000. The etiology was ischemic heart disease in 154, idiopathic cardiomyopathy in 130 and other in 8 patients. NYHA class was I in 7%, II in 50.6% and III in 42.4% of the patients. Two years was defined as the maximum follow-up time; it was 551.5 +/- 242.2 days on average, and 62 events (death or cardiac transplantation) occurred. The following parameters were analyzed: peak VO2 (l/min and ml/kg/min), percent predicted peak VO2 (pred VO2) (l/min and ml/kg/min), VO2 every 15 seconds (sec) of the first 3 minutes of recovery (the difference between peak VO2/kg and VO2/kg every 15 sec in the recovery period (dif VO2), expressed in ml/kg/min, and also the time (sec) to reach 50% of peak VO2 (T1/2). It was considered that a combined end-point was reached if patients died or underwent cardiac transplantation. RESULTS: ROC curves of these parameters showed the following as cut-off values (area under the curve > 0.7) for the occurrence of events: peak VO2 < 60% of pred VO2, dif VO2 at 60 sec (< 3 ml/kg/min), 90 sec (< 5), 120 sec (< 8), 150 sec (< 8.6) and 180 sec (< 10.5) of the recovery and T1/2 > 115 sec. Survival analysis was performed considering pred VO2 < 60%, dif VO2 at 150 sec (the largest area under the curve) and T1/2 > 115 sec. In the survival analysis, when the decrease in VO2 at 150 sec was less than 8.6 ml/kg/min the number of patients with events increased from 9.2% to 43.5% (p < 0.001; log-rank), and when T1/2 was less than 115 sec the number of events increased from 12.3 to 34.2% (p < 0.001; log-rank). When the criteria of T1/2 and dif VO2 at 150 sec were considered together with pred VO2 < 60%, mortality increased from 31 to 54% and from 33 to 51%, respectively (p < 0.001, for both parameters; chi-square). CONCLUSIONS: A slow VO2 kinetics in the recovery period of the CPET by itself identified groups of patients with poor prognosis. The association of these parameters with peak VO2 enhanced the identification of groups at greater risk for events. A global evaluation of the CPET should be performed, considering other parameters besides peak VO2, particularly those related to VO2 kinetics in recovery (T1/2 and dif VO2 at 150 sec) as identified in this study.