The role of exercise testing and gas-exchange measurement in the prognostic assessment of patients with heart failure.

Functional impairment has long been recognized as an important factor in the risk paradigm among patients with heart disease. In chronic heart failure, this issue has been even more important in recent years because of the steady growth in the number of patients awaiting heart transplantation relative to the available pool of donor hearts. The use of gas-exchange techniques to assess patients with heart failure has attracted interest because these techniques provide a more precise, reproducible, objective, and physiologic expression of exercise tolerance. Numerous studies published in the 1990s demonstrate that maximal oxygen uptake (peak VO2) is an independent predictor of mortality in patients with heart failure. Achievement of a peak VO2 that is less than 14 mL/kg/min has been recognized as one of the relative indications for transplantation, because patients who achieve a measurement that is higher than 14 mL/kg/min have a 1-year mortality rate similar to that of patients who undergo transplantation (i.e., > 90%). However, some debate exists regarding the optimal cutpoint that separates survivors from nonsurvivors, and studies have not consistently defined the timing of the test relative to optimization of medical therapy. It has also been debated which hemodynamic variables, at rest or during exercise, should be used in combination with peak VO2 to optimally stratify risk in these patients. This article reviews the applications of cardiopulmonary exercise testing in prognosis among patients with chronic heart failure.