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

Abstract

Abstract 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 (peakṼO2). 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 peakṼO2 was 13.5 ± 3.5 ml/kg/min in HF patients and 28.1 ± 7.4 ml/kg/min in healthy (P < 0.001). 6MWT-ṼO2 was 98 ± 20% of the CPET peakṼO2 values in HF patients, while 72 ± 20% in healthy subjects (P < 0.001). 6MWT-ṼO2 was >110% of CPET peakṼO2 in 42% of more severe HF patients (peakṼO2 <12 ml/kg/min). Similar results have been found for ventilation and heart rate. Of note, the slope of the relationship between ṼO2 at 6MWT, reported as percentage of CPET peakṼO2 vs. 6MWT ṼO2 reported as absolute value, progressively increased as exercise limitation did. Conclusions 6MWT must be perceived as a maximal or even supra-maximal exercise activity at least in patients with severe exercise limitation from HF. Our findings should influence the safety procedures needed for the 6MWT in HF.