Intravenous Iron to Improve Symptoms, Quality of Life and Exercise Capacity in HFpEF With Iron Deficiency

This study will investigate whether intravenous (IV) iron improves symptoms, exercise capacity, and quality of life in patients with heart failure with preserved ejection fraction (HFpEF) and iron deficiency. Iron deficiency is common in heart failure and is associated with worse symptoms, reduced physical activity, poorer quality of life, and increased hospitalisation risk. Intravenous iron therapy has demonstrated clinical benefit in patients with heart failure with reduced ejection fraction (HFrEF), but evidence in HFpEF remains limited. ISLE-HFpEF is a prospective, randomised, double-blind, placebo-controlled trial enrolling 150 adults with symptomatic HFpEF and iron deficiency. Participants will be randomised in a 1:1 ratio to receive either intravenous ferric derisomaltose (Monofer) or placebo (0.9% sodium chloride). Participants will undergo baseline assessment, treatment infusion, and 12-week follow-up. The primary outcome is change in 6-minute walk distance at 12 weeks. Secondary outcomes include change in Kansas City Cardiomyopathy Questionnaire (KCCQ) score, physical activity measured using wearable accelerometers, transferrin saturation, NT-proBNP, and New York Heart Association (NYHA) functional class. The study will also evaluate the feasibility and utility of continuous digital monitoring using wearable technologies, including a thigh-worn SENS Motion accelerometer and the Oura Ring, to assess real-world physical activity and cardiovascular physiology throughout the study period.

Inclusion Criteria: * Age ≥18 years. * Willing and able to provide written informed consent. * Clinical diagnosis of heart failure with preserved ejection fraction (HFpEF). * New York Heart Association (NYHA) class II or III symptoms at the time of randomisation. * Ambulatory for at least 7 days prior to randomisation. * Iron deficiency defined as transferrin saturation (TSAT) \