Exercise endpoints in patients with chronic heart failure

Background: Peak oxygen consumption ( vO2) is a powerful predictor of outcome in patients with chronic heart failure. This is not a test that is readily clinically available. We therefore sought to establish a method of assessing peak vO2 from non-invasively acquired data. Methods: We analysed the results from incremental treadmill exercise tests in 60 patients [aged 59.0 (S.D. 12.4) years] with chronic heart failure or left ventricular dysfunction [left ventricular ejection fraction (29.6 (15.2)%)] and 52 control subjects [aged 36.7 (12.3)]. Metabolic gas exchange during exercise was measured with a respiratory mass spectrometer. Heart rate and blood pressure were measured. Results: Peak O2 was lower in patients than controls [19.9 (7.7) ml/kg/min vs. 38.3 (9.0), P<0.001]. Exercise time (r=0.84, P<0.001), heart rate at peak exercise (r=0.63, P<0.0001), change in heart rate (r=0.72, P<0.0001), rate pressure product at peak exercise (r=0.64, P<0.0001) and change in systolic blood pressure (r=0.31, P=0.002) all correlated with peak vO2. In a stepwise regression model, exercise time was the most powerful predictor of peak vO2 (r2=0.79). The only additional independent variable was change in heart rate from rest to peak exercise, which increased r2 to 0.80. In a survival analysis, measured peak vO2 and the peak vO2 estimated from exercise time and change in heart rate had similar predictive power. Conclusions: In this preliminary study, peak vO2 can be estimated from non-invasively acquired parameters. Estimated peak vO2 and measured peak vO2 have similar predictive power for outcome. Further work is necessary to see if estimated peak vO2 is widely applicable in a clinical setting.