Usefulness of oxygen uptake efficiency slope in a 6 min walk test in chronic heart failure.

Kim MS;  Pusan National University Hospital, Busan, Republic of Korea.
Bong W; Choi JH; Shin MJ; Lee BJ;

ESC heart failure [ESC Heart Fail] 2024 Mar 26.
Date of Electronic Publication: 2024 Mar 26.

Aims: Frailty is an obstacle to performing cardiopulmonary exercise test (CPET) in patients with chronic heart failure (CHF). We evaluated the usefulness of oxygen uptake efficiency slope (OUES) using a 6 min walk test (6MWT) with portable gas analysis compared with CPET-derived parameters in patients with CHF.
Methods and Results: Patients with CHF who underwent both the 6MWT with portable gas analysis and CPET between December 2016 and May 2020 were retrospectively investigated. The 6MWT-derived and echocardiographic parameters were compared with the OUES and peak oxygen consumption (VO 2 ) from the CPET. Forty patients were analysed; 50% were male with a mean age of 55.45 ± 14.70 years. Twenty-six patients (65%) had New York Heart Association Functional Classification II or III dyspnoea. Twenty-five patients (62.5%) had heart failure (HF) with preserved ejection fraction (EF) (left ventricular EF > 50%), and nine patients (22.5%) had HF with reduced EF (EF < 40%). During the 6MWT, the peak VO 2 was 14.97 ± 3.80 mL/kg/min, which was only 74% of the peak VO 2 in the CPET, 20.18 ± 5.64 mL/kg/min. The OUES in the 6MWT was lower than that in the CPET (1528.87 ± 579.01 in the 6MWT vs. 1638.69 ± 601.31 in the CPET). The 6 min walk distance (6MWD) and OUES in the 6MWT were positively correlated with the OUES in the CPET (6MWD, r = 0.434, P = 0.005; OUES, r = 0.729, P < 0.001). The OUES in the 6MWT showed the strongest correlation with the OUES in the CPET. When we divided patients into two groups according to peak VO 2 in the CPET, the correlation between OUES values of the 6MWT and that of the CPET was consistently confirmed (peak VO 2  ≥ 20 mL/kg/min group, r = 0.661, P = 0.001; peak VO 2  < 20 mL/kg/min group, r = 0.526, P = 0.021). In addition, the 6MWD, OUES, and peak VO 2 in the 6MWT were associated with peak VO 2 in the CPET (6MWD, r = 0.627, P < 0.001; OUES, r = 0.452, P = 0.003; and peak VO 2 , r = 0.492, P = 0.001).
Conclusions: In frail patients with CHF who have difficulty performing maximal exercises, the OUES through the 6MWT may be applied instead of the OUES and peak VO 2 from the CPET.