Exercise-induced oxygen desaturation reveals early post-discharge vulnerability in heart failure

Background

Early rehospitalisation following discharge represents a vulnerable transition phase in patients with heart failure (HF) and remains a major unmet clinical challenge. We previously demonstrated that exercise-induced oxygen desaturation (ΔSpO2-Ex) during the 6-minute walk test (6MWT) predicts long-term outcomes. Whether this physiological marker also identifies risk during the early post-discharge period remains unknown.

Purpose

To evaluate the prognostic value of ΔSpO2-Ex for predicting 90-day clinical outcomes in patients hospitalised for acute HF.

Methods

In this prospective observational study, 82 consecutive patients admitted with acute HF underwent a standardised 6MWT prior to discharge with continuous peripheral oxygen saturation (SpO2) monitoring. ΔSpO2-Ex was defined as the difference between maximum resting SpO2 and mean SpO2 during the 6MWT. Patients were followed for 90 days for a composite endpoint of HF rehospitalisation or cardiovascular death. Associations between ΔSpO2-Ex and outcomes were assessed using Cox proportional hazards models.

Results

The mean age was 78.4 years, and 48% were female. The median 6-minute walk distance (6MWD) was 295 m, and the median ΔSpO2-Ex was 4.2%. Patients were categorised according to the median values of both parameters. Kaplan–Meier analysis demonstrated a significantly higher risk of the composite endpoint in patients with 6MWD ≤295 m compared with those walking >295 m (HR 4.66, 95% CI 1.33–16.37, p=0.016). Similarly, patients with ΔSpO2-Ex ≥4.2% had a significantly increased risk of events compared with those with ΔSpO2-Ex <4.2% (HR 4.80, 95% CI 1.37–16.85, p=0.014). When analysed as a continuous variable, ΔSpO2-Ex remained strongly associated with outcomes; each 1% increase in SpO2 decline was associated with a 13% higher risk of the composite endpoint (HR 1.13; 95% CI 1.04–1.22; p=0.002).

The magnitude of risk associated with ΔSpO2-Ex was comparable to that observed for 6MWD, and ΔSpO2-Ex remained independently associated with outcomes after multivariable adjustment including age, 6MWD, LVEF, and NT-proBNP. These findings suggest that impaired peripheral oxygen dynamics during submaximal exercise reflect underlying haemodynamic and microcirculatory vulnerability in the early post-discharge phase.

Conclusions

ΔSpO2-Ex identifies patients at heightened risk during the vulnerable 90-day period following HF discharge. Extending its previously demonstrated long-term prognostic value, this simple and non-invasive physiological marker provides incremental risk information beyond functional capacity and conventional clinical parameters, supporting its potential role in personalised early post-discharge management strategies.Kaplan–Meier analysis of 90-day outcomes