Kinetics of oxygen consumption during and after exercise in patients with dilated cardiomyopathy New markers of exercise intolerance with clinical implications

Objectives. This study analyzed the kinetics of oxygen consumption during and after maximal cardiopulmonary exercise test in patients with dilated cardiomyopathy. The prognostic information derived from indexes of recovery was also studied. Background. Previous studies have examined the kinetics of oxygen consumption during short recovery period in limited number of patients. To our knowledge, no study has examined the prognostic information derived from indexes of recovery. Methods. We studied 153 patients and 55 control subjects. We calculated the ratio between total oxygen consumption during exercise and recovery, the half-recovery time of peak oxygen consumption, the time constant of recovery, the recovery time and the ratio between duration of exercise and recovery time. Results. Recovery of oxygen consumption was significantly delayed in patients, and this delay was related to the degree of exercise intolerance. After median follow-up period of 439 days, for the total study group, percent of predicted peak oxygen consumption (p = 0.003) and ejection fraction (p = 0.03) were independent predictors of survival. In subgroup of patients with moderate exercise intolerance (percent peak oxygen consumption >40%), the ratio between total oxygen consumption during exercise and recovery (p = 0.013) and the ejection fraction (p = 0.013) were independent predictors of survival. Conclusions. The kinetics of oxygen consumption during recovery was delayed in patients with dilated cardiomyopathy. Although indexes of recovery were not prognostic markers in the total study group, the ratio between total oxygen consumption during exercise and recovery was an independent prognostic marker in patients with moderate exercise intolerance.