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

Heart failure with preserved ejection fraction (HFpEF) accounts for approximately half of all heart failure cases and is associated with substantial morbidity, reduced exercise capacity, impaired quality of life, and frequent hospitalisation. Iron deficiency is highly prevalent in patients with heart failure and may be even more common in HFpEF than in heart failure with reduced ejection fraction (HFrEF). In heart failure populations, iron deficiency has been associated with impaired functional capacity, reduced quality of life, and adverse cardiovascular outcomes.

Intravenous (IV) iron therapy has demonstrated symptomatic and functional benefits in multiple randomised trials in patients with HFrEF and iron deficiency, leading to incorporation into contemporary heart failure guidelines. However, evidence supporting IV iron therapy in HFpEF remains limited. The FAIR-HFpEF trial suggested potential improvements in exercise capacity following IV iron therapy, but recruitment challenges resulted in early termination and limited statistical power. Additional adequately powered studies are therefore required to evaluate the efficacy of IV iron in HFpEF.

Iron plays a central role in mitochondrial oxidative phosphorylation and cellular energy production. Impaired myocardial energetics have been demonstrated in iron-deficient heart failure patients and may be particularly relevant in HFpEF, where diastolic relaxation is an energy-dependent process. Restoration of iron stores may therefore improve exercise tolerance, symptoms, and functional status in patients with HFpEF.

ISLE-HFpEF is a prospective, randomised, double-blind, placebo-controlled, parallel-group trial evaluating the effects of intravenous ferric derisomaltose (Monofer) in adults with symptomatic HFpEF and iron deficiency. A total of 150 participants will be randomised in a 1:1 ratio to receive either a single infusion of ferric derisomaltose (up to 20 mg/kg) or placebo (0.9% sodium chloride). Participants will undergo baseline assessment, randomisation and infusion after a two-week run-in period, and follow-up assessment 12 weeks after treatment.

The primary objective is to determine whether IV iron improves exercise capacity, assessed by change in 6-minute walk distance at 12 weeks. Secondary objectives include assessment of quality of life, symptom burden, biochemical markers, and functional status.

The study will also investigate the use of wearable technologies as digital endpoints in cardiovascular clinical trials. Participants will wear a SENS Motion thigh-worn accelerometer continuously for 12 weeks to measure habitual physical activity, including daily step count, physical activity intensity, and sedentary behaviour. Participants will additionally use the Oura Ring Generation 4 to collect exploratory physiological metrics including heart rate variability, resting heart rate, respiratory rate, activity patterns, and estimated cardiorespiratory fitness. These devices are intended to provide objective measures of real-world functional status and behavioural change that may complement traditional clinic-based assessments.

Safety assessments will include monitoring for adverse events and infusion-related hypersensitivity reactions throughout the study period.