A non-linear pattern of exercise capacity in heart failure across ejection fraction categories.

This study aimed to compare exercise capacity (EC) and comorbidity profiles across left ventricular ejection fraction (LVEF) defined heart failure (HF) categories. From a retrospective, single-centre registry, we analysed 196 individuals with established HF who underwent cardiopulmonary exercise testing and a 6 min walk test (6MWT). EC differed significantly across LVEF categories but not in a linear fashion. The percent of predicted peak oxygen uptake (VO₂) was significantly lower in HF with reduced LVEF (HFrEF, n = 89) than in HF with preserved LVEF (HFpEF, n = 36) and HF with mildly reduced LVEF (HFmrEF, n = 71) (65.9% vs. 76.6% and 76.8%, p < 0.001). Ventilatory inefficiency (VE/VCO₂ slope) was more pronounced in HFrEF than in HFpEF (35.3 vs. 31.7; p = 0.002), while the proportion with VE/VCO₂ slope > 36 did not differ across groups. The achieved workload and 6MWT distance were comparable across groups. Comorbidity profiles diverged meaningfully: HFmrEF had the lowest prevalence of chronic kidney disease (p = 0.009) and type 2 diabetes (p = 0.025). Notably, HFpEF exhibited the highest prevalence of anaemia (p = 0.0013). HFmrEF displays an EC profile closer to HFpEF than to HFrEF, while anaemia emerges as a particularly important comorbidity in HFpEF.