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 (peak(V) over-dotO(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 peak(V) over-dotO(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-(V) over-dotO(2) was 98 +/- 20% of the CPET peak(V) over-dotO(2) values in HF patients, while 72 +/- 20% in healthy subjects (P < 0.001). 6MWT-(V) over-dot was >110% of CPET peak(V) over-dotO(2) in 42% of more severe HF patients (peak(V) over-dotO(2) < 12 mL/kg/min). Similar results have been found for ventilation and heart rate. Of note, the slope of the relationship between (V) over-dotO(2) at 6MWT, reported as a percentage of CPET peak(V) over-dotO(2) vs. 6MWT (V) over-dotO(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.