Prognostic significance of oxygen uptake kinetics during low level exercise in patients with heart failure

Peak oxygen consumption (VO2) reflects the severity of congestive heart failure (CHF) and is widely accepted as a good prognostic marker.(1,2) However, there is increasing interest in obtaining submaximal exercise testing because of several reasons. First, peak VO2, is not necessarily a reliable parameter of cardiovascular capacity because patient motivation and conditions other than cardiopulmonary diseases may influence it.(3) In addition, it has been recently shown in patients early after myocardial infarction with impaired ejection fraction that the increase in cardiac output at exercise onset may be delayed while the maximal cardiac output is still normal.(4) Finally, patients hardly perform maximal exercise during daily life. Accordingly, submaximal exercise testing has been increasingly used to assess functional capacity of patients with CHF.(5-7) Parameters not requiring maximal exercise (e.g., 6-minute walking distance, ventilation/carbon dioxide [CO2] output slope) may predict morbidity and mortality in these patients.(7,8) Although kinetics of VO2, at exercise onset are altered in patients with CHF,(4,9) their prognostic value has not yet been determined. Thus, we sought to prospectively investigate whether VO2 kinetics may be useful for the prognostic assessment of patients with chronic CHF compared with a variety of previously described predictors of prognosis.(2,10,11)