Peak VO2 as a Predictor of Ambulatory Activity of Daily Living in Patients with Chronic Heart Failure

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Background: The 2009 Update on ACC/AHA Guidelines for the Management of Heart Failure emphasize the importance of assessing the functional capacity and the activity of daily living in heart failure patients. Though the 6 minute walk test has shown prognostic significance, serial changes in walking distance may not parallel changes in clinical status. The peak oxygen uptake (Peak VO2) determined by cardiopulmonary exercise testing provides the most objective assessment of functional capacity in patients with heart failure. However, peak V02 has been found to correlate poorly with other activity measures such as the 6 minute walk test. It is unknown whether peak V02 correlates with routine ambulatory activities of daily living(RAADL). Methods and Results: In a cross sectional study of 42 ambulatory patients (age 52 ± 8 years; left ventricular ejection fraction 23.6%±9%; 34 males; 31 NYHA class I/II and 11 NYHA class III/IV) with chronic heart failure secondary to systolic dysfunction, percent predicted Peak VO2 was measured by cardiopulmonary exercise testing. All patients achieved anaerobic threshold and 40 of the 42 reached a respiratory quotient > 1.05. The RAADL was measured using a pedometer during a two week period immediately following exercise testing. We examined the association between percent predicted Peak VO2 and RAADL using linear regression. A modest but significant linear correlation (r=0.4, p=0.0079) was found between peak VO2 and RAADL. A similar relationship was observed between the VO2 at anaerobic threshold and RAADL (r=0.47, p=0.0017). In subgroup analysis, patients with mild heart failure (NYHA class I/II) showed a significant correlation (r=0.45, p=0.0107) which was not seen in patients with NYHA class III/IV symptoms (r=0.17, p=0.6101). However, the number of patients in the latter group was much smaller. Conclusion: Better performance during cardiopulmonary exercise testing is associated with greater ambulatory activity in patients with chronic heart failure secondary to systolic dysfunction. This association may be limited only to patients with mild heart failure (NYHA class I/II). Therefore, although peak V02 correlates poorly with measures such as the 6 minute walk test, in at least some of the patients with congestive heart failure, it does correlate well with the capacity to perform usual activities of daily living. These findings require reexamination of metabolic testing as a measure of daily functional capacity as well as maximal exercise tolerance.