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 fai lure (CHF) and is widely accepted as a good prognostic marker.(1,2) However , there is increasing interest in obtaining submaximal exercise testing bec ause of several reasons. First, peak VO2, is not necessarily a reliable par ameter of cardiovascular capacity because patient motivation and conditions other than cardiopulmonary diseases may influence it.(3) In addition, it h as been recently shown in patients early after myocardial infarction with i mpaired ejection fraction that the increase in cardiac output at exercise o nset may be delayed while the maximal cardiac output is still normal.(4) Fi nally, patients hardly perform maximal exercise during daily life. Accordingly, submaximal exercise testing has been increasingly used to asse ss functional capacity of patients with CHF.(5-7) Parameters not requiring maximal exercise (e.g., 6-minute walking distance, ventilation/carbon dioxi de [CO2] output slope) may predict morbidity and mortality in these patient s.(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, w e sought to prospectively investigate whether VO2 kinetics may be useful fo r the prognostic assessment of patients with chronic CHF compared with a va riety of previously described predictors of prognosis.(2,10,11)