Brisk walking can be a maximal effort in heart failure patients: a comparison of cardiopulmonary exercise and 6 min walking test cardiorespiratory data

AIMS: Cardiopulmonary exercise test (CPET) and 6 min walking test (6MWT) are frequently used in heart failure (HF). CPET is a maximal exercise, whereas 6MWT is a self‐selected constant load test usually considered a submaximal, and therefore safer, exercise, but this has not been tested previously. The aim of this study was to compare the cardiorespiratory parameters collected during CPET and 6MWT in a large group of healthy subjects and patients with HF of different severity. METHODS AND RESULTS: Subjects performed a standard maximal CPET and a 6MWT wearing a portable device allowing breath‐by‐breath measurement of cardiorespiratory parameters. HF patients were grouped according to their CPET peak oxygen uptake (peakV̇O(2)). One hundred and fifty‐five subjects were enrolled, of whom 40 were healthy (59 ± 8 years; male 67%) and 115 were HF patients (69 ± 10 years; male 80%; left ventricular ejection fraction 34.6 ± 12.0%). CPET peakV̇O(2) was 13.5 ± 3.5 mL/kg/min in HF patients and 28.1 ± 7.4 mL/kg/min in healthy subjects (P < 0.001). 6MWT‐V̇O(2) was 98 ± 20% of the CPET peakV̇O(2) values in HF patients, while 72 ± 20% in healthy subjects (P < 0.001). 6MWT‐V̇O(2) was >110% of CPET peakV̇O(2) in 42% of more severe HF patients (peakV̇O(2) < 12 mL/kg/min). Similar results have been found for ventilation and heart rate. Of note, the slope of the relationship between V̇O(2) at 6MWT, reported as a percentage of CPET peakV̇O(2) vs. 6MWT V̇O(2) reported as the absolute value, progressively increased as exercise limitation did. CONCLUSIONS: In conclusion, the last minute of 6MWT must be perceived as a maximal or even supramaximal exercise activity in patients with more severe HF. Our findings should influence the safety procedures needed for the 6MWT in HF.