Abstract 1716: The Ventilatory Anaerobic Threshold in Heart Failure: A Multi-Center Evaluation of Reliability
Background: The ventilatory threshold (VT) is generally considered to be an effort-independent index of exercise capacity and has been suggested as a potential objective endpoint for studies of heart failure therapies. The VT is usually determined by visual assessment of the point where VCO2 increases non-linearly with respect to VO2 (the V-Slope method). We quantified the reliability of VT determination using data from a multicenter study in patients with heart failure (HF).
Methods and Results: The FIX-HF-5 randomized study of cardiac contractility modulation enrolled 428 patients with ejection fraction ≤35% and NYHA III or IV symptoms from 50 centers in the US. Cardiopulmonary exercise tests were performed at baseline, and 12, 24 and 50 weeks after randomization which provided 1679 tests. The VT was determined from each test in a core laboratory by two independent Readers. The VT could not be determined for 276 tests (16.4% indeterminate). Inter-observer variability (coefficient of variation [CoV]) was 20.2% between the two Readers. Intra-observer variability was assessed by resubmitting (blinded) 200 tests to the same Readers; the CoV was 17% for Reader 1 and 25% for Reader 2. One hundred tests were submitted to two additional Readers at a second core laboratory. Inter-observer variability in the second laboratory was 26.7%. Inter-lab variability was 21.5%.
Conclusions: The VT is indeterminate in a relatively large percentage of tests. Inter-observer, intra-observer and inter-site determination of the VT range between 17 and 27%. This variation should be considered when using the VT as an endpoint in clinical trials of HF.