Rationale:
Peak oxygen consumption (VO2) and the minute ventilation (VE)-carbon dioxide production (VCO2) slope provide prognostic information in the heart failure (HF) population. The Weber classification system is a well established method for categorizing patients according to peak VO2, but it is unknown whether ventilatory efficiency adds prognostic value within the Weber classifications.
Objectives:
To assess the added prognostic value of the VE/VCO2 slope to the Weber classification system in patients diagnosed with HF.
Methodology:
Four hundred and twenty-two subjects (340 male/82 female, 227 ischemic/195 non-ischemic, mean age: 56.9 +/- 13.1 years) participated in this analysis. Mean left ventricular ejection fraction was 33.3 +/- 12.3%. Peak VO2 and the VE/VCO2 slope were determined via cardiopulmonary exercise testing. Subjects were tracked for cardiac-related mortality following the exercise test.
Results:
The numbers of subjects in Weber Classes A-B were 97, 105, 172 and 48, respectively. Seventy-nine cardiac related deaths occurred during the 31.6 +/-25.9 month tracking period. The annual mortality rate for the overall group was 9.7%. Kaplan-Meier analysis revealed event-free survival for subjects in Weber Classes A-B was 91.8%, 85.7%, 75.0% and 72.9%, respectively (log-rank test chi-square = 16.6, P = 0.001). Analysis of variance revealed the VE/VCO2 slope was significantly different amongst the four Weber class groups [A: 28.2 (+/-4.9), B: 31.0 (+/-5.8), C: 36.0 (+/-7.5), D: 43.0 (+/-11.1), P < 0.05]. Receiver operating characteristic (ROC) curve analysis revealed the VE/VCO2 slope prognostic classification schemes were significant in each of the four Weber classes (Table 1).
Conclusions:
The results of the present study indicate that the VE/VCO2 slope is able to improve the identification of individuals at higher risk for mortality within each Weber class. These findings further support the clinical assessment of ventilatory efficiency in the heart failure population.