Validation of Exercise Capacity as a Surrogate Endpoint in Exercise-Based Rehabilitation for Heart Failure: A...

This study sought to validate exercise capacity (EC) as a surrogate for mortality, hospitalization, and health-related quality of life (HRQOL).

EC is often used as a primary outcome in exercise-based cardiac rehabilitation (CR) trials of heart failure (HF) via direct cardiorespiratory assessment of maximum oxygen uptake (Vo₂peak) or through submaximal tests, such as the 6-min walk test (6MWT).

After a systematic review, 31 randomized trials of exercise-based CR compared with no exercise control (4,784 HF patients) were included. Outcomes were pooled using random effects meta-analyses, and inverse variance weighted linear regression equations were fitted to estimate the relationship between the CR on EC and all-cause mortality, hospitalization, and HRQOL. Spearman correlation coefficient (ρ), R² at trial level, and surrogate threshold effect (STE) were calculated. STE represents the intercept of the prediction band of the regression line with null effect on the final outcome.

Exercise-based CR is associated with positive effects on EC measured through Vo₂peak (+3.10 ml/kg/min; 95% confidence interval [CI]: 2.01 to 4.20) or 6MWT (+41.15 m; 95% CI: 16.68 to 65.63) compared to control. The analyses showed a low level of association between improvements in EC (Vo₂peak or 6MWT) and mortality and hospitalization. Moderate levels of correlation between EC with HRQOL were seen (e.g., R² <52%; |ρ| < 0.72). Estimated STE was an increase of 5 ml/kg/min for Vo₂peak and 80 m for 6MWT to predict a significant improvement in HRQOL.

The study results indicate that EC is a poor surrogate endpoint for mortality and hospitalization but has moderate validity as a surrogate for HRQOL. Further research is needed to confirm these findings across other HF interventions.