Delayed anaerobic threshold in heart failure patients with atrial fibrillation

Purpose: To assess whether atrial fibrillation (AF) in heart failure (HF) affects oxygen uptake at anaerobic threshold (V E O 2 AT) and heart rate (HR) kinetics. METHODS: A total of 15 patients with HF and AF and 18 with HF and sinus rhythm (SR) performed a maximal incremental and 2 constant workload cycle ergometer cardiopulmonary exercise tests (below and above AT, at 25% and 75% of maximal workload, respectively). At constant workload tests, kinetics of VO₂ and HR were assessed by calculating time constant (τ).RESULTS: HF patients with AF showed a similar peak VO₂ to those with SR (16.7±4.5 mL/kg/min vs 16.6±3.9 mL/kg/min). However, VO₂ AT (11.3±2.9 mL/kg/min vs 9.3±2.8 mL/kg/min; P 2 below and above AT were not significantly different.CONCLUSIONS: In HF patients with AF, despite a similar peak VO₂ compared with patients with HF and SR, VO₂ AT is higher because of a higher HR and a greater HR increase during exercise. One postulated mechanism would be a greater cardiac output increase at the beginning of exercise in HF patients with AF. The delayed AT generates uncertainty about the meaning of a VO₂ value at AT in HF patients with AF, because a higher AT is usually associated with better performance and a better prognosis.