The Six-Minute Step Test as a Predictor of Functional Capacity according to Peak VO₂ in Cardiac Patients

Abstract

Background:

Six-minute step test (6MST) is a simple way to evaluate functional capacity, although it has not been well studied in patients with coronary artery disease (CAD) or heart failure (HF).

Objective:

Analyze the association between the 6MST and peak oxygen uptake (VO_2peak) and develop an equation for estimating VO_2peak based on the 6MST, as well as to determine a cutoff point for the 6MST that predicts a VO_2peak ≥20 mL.Kg^-1.min^-1

Methods:

In 171 patients who underwent the 6MST and a cardiopulmonary exercise test, correlation, regression, and ROC analysis were used and a p < 0.05 was admitted as significant.

Results:

mean age was 60±14 years and 74% were male. Mean left ventricle ejection fraction was 57±16%, 74% had CAD and 28% had HF. Mean VO_2peak was 19±6 mL.Kg^-1.min^-1 and mean 6MST performance was 87±45 steps. Association between 6MST and VO_2peak was r 0.69 (p <0.001). The model VO_2peak =19.6 + (0.075 x 6MST) – (0.10 x age) for men and VO_2peak =19.6 + (0.075 x 6MST) – (0.10 x age) – 2 for women could predict VO_2peak based on 6MST results (adjusted R 0.72; adjusted R² 0.53). The most accurate cutoff point for 6MST to predict a VO_2peak ≥20 mL.Kg^-1.min^-1 was >105 steps (AUC 0.85; 95% CI 0.79 -0.90; p <0.001).

Conclusion:

An equation for predicting VO_2peak based on 6MST results was derived, and a significant association was found between 6MST and VO_2peak. The cutoff point for 6MST, which predicts a VO_2peak ≥20 mL.Kg^-1.min^-1, was >105 steps. (Arq Bras Cardiol. 2021; 116(5):889-895)

Keywords:
Heart Failure; Oxygen Consumption; Respiratoty Capacity; Tidal Volume; Exercise Test; Prognóstico; Mortalidade