Heart failure with preserved ejection fraction represents a pervasive and debilitating clinical challenge worldwide. Systemic iron deficiency affects more than half of this population, significantly worsening functional limitations, hospitalizations, and quality of life. Fortunately, recent breakthrough clinical research offers promising therapeutic possibilities. Specifically, the groundbreaking IRONMET-HFpEF randomized trial evaluated the physiological impact of targeted iron repletion in HFpEF to determine whether intravenous iron administration enhances objective cardiorespiratory performance. The trial results deliver compelling evidence that restoring intracellular iron stores effectively alleviates severe exercise intolerance in this growing patient cohort.

Pathophysiology of Iron Deficiency in Heart Failure

Systemic iron deficiency frequently arises in heart failure, developing independently of peripheral anemia. In chronic heart failure, sustained inflammatory signaling triggers hepatic secretion of hepcidin, the primary regulator of systemic iron balance. Consequently, high circulating hepcidin degrades ferroportin channels on duodenal enterocytes, suppressing intestinal iron absorption and trapping stored iron inside macrophages. This functional block deprives high-turnover metabolic tissues of essential elemental iron, particularly targeting cardiomyocytes and skeletal myocytes. Within these active tissues, iron acts as an obligatory cofactor for mitochondrial electron transport chains, citric acid cycle enzymes, and myoglobin-dependent oxygen transport. Therefore, intracellular iron starvation diminishes cellular adenosine triphosphate production, precipitating early skeletal muscle fatigue and impaired oxygen extraction during exertion. Furthermore, observational data confirm that iron-deficient heart failure patients experience worse functional capacity, more frequent hospitalizations, and decreased long-term survival. Traditional oral iron therapy consistently fails in this setting because elevated hepcidin prevents intestinal uptake. Consequently, intravenous iron replacement represents the optimal clinical solution to bypass mucosal barriers, re-establish physiological tissue iron levels, and restore cellular energetics.

Trial Design and Protocol of IRONMET-HFpEF

To investigate whether parenteral iron improves objective functional indices, investigators conducted the IRONMET-HFpEF trial at the Mass General Brigham Heart and Vascular Institute. Specifically, this investigator-initiated, double-blind, placebo-controlled clinical trial enrolled 65 symptomatic participants with diagnosed preserved ejection fraction and documented iron deficiency. Trial investigators defined iron deficiency as a serum ferritin concentration below 100 ng/mL, or 100 to 299 ng/mL with a transferrin saturation below 20%. Notably, women comprised 72% of the participants, with a median age of 68 years, mirroring real-world epidemiological demographics. Researchers randomized participants in a 2:1 ratio to receive either a single 1,000-mg infusion of ferric derisomaltose or an identical saline placebo. Moreover, the team used specialized opaque infusion covers to maintain double-blinding, successfully concealing the dark coloration of the iron solution from participants and evaluators. All participants completed standardized cardiopulmonary exercise testing and clinical assessments at baseline and 12 weeks post-infusion. Ultimately, this rigorous protocol provided an objective physiological evaluation of cardiorespiratory performance rather than relying merely on subjective symptom scores.

Primary Endpoints and Objective Functional Outcomes

The primary efficacy endpoint evaluated the change in peak oxygen uptake measured during cardiopulmonary exercise testing between baseline and 12 weeks. Peak oxygen uptake represents the definitive gold standard for assessing integrated cardiopulmonary and peripheral muscular performance. Remarkably, patients receiving ferric derisomaltose achieved an approximate 10% improvement in peak oxygen consumption over 12 weeks. In contrast, participants assigned to the placebo group exhibited no meaningful change in peak oxygen uptake. Furthermore, this objective physiological gain translated into substantial functional progress during daily activities. Patients treated with ferric derisomaltose achieved a statistically significant between-group increase of 41.1 meters in six-minute walk distance compared to placebo. In addition, secondary assessments revealed meaningful improvements in patient-reported quality of life measures. Importantly, the single intravenous infusion demonstrated exceptional safety and tolerability, with adverse event frequencies remaining comparable between active and control arms. Crucially, these findings demonstrate that targeted parenteral iron replenishment produces tangible, clinically meaningful functional recovery in patients burdened by exertional intolerance. Consequently, clinicians gain a potent therapeutic tool to improve daily exercise tolerance.

Mechanisms Underlying Iron Repletion in HFpEF

To understand why parenteral iron yields such pronounced functional gains, clinicians must examine peripheral and central pathophysiology in preserved ejection fraction. Although cardiologists traditionally focused on intracardiac filling pressures and diastolic stiffness, contemporary evidence demonstrates that peripheral abnormalities drive substantial exercise intolerance. Specifically, skeletal muscle wasting, microvascular endothelial dysfunction, capillary rarefaction, and mitochondrial metabolic impairment restrict peripheral oxygen extraction during physical activity. By administering intravenous ferric derisomaltose, clinicians deliver stable carbohydrate-bound iron complexes directly into systemic circulation. Subsequently, the reticuloendothelial system processes these complexes, enabling rapid iron uptake by skeletal myocytes and cardiomyocytes. Therefore, intracellular iron availability restores mitochondrial cytochrome activity and respiratory chain efficiency, allowing muscles to generate adenosine triphosphate aerobically. Additionally, iron replenishment enhances microvascular endothelial nitric oxide bioavailability, promoting peripheral vasodilation and muscle perfusion during exertion. Consequently, targeted iron repletion in HFpEF corrects both skeletal muscle bioenergetics and microvascular dysfunction, explaining the marked improvements observed in aerobic endurance and functional physical reserve.

Clinical Implications and Future Therapeutic Horizons

The outcomes of the IRONMET-HFpEF study offer immediate, actionable insights for daily clinical practice. Clinicians frequently miss iron deficiency in ambulatory patients who present with normal hemoglobin levels, assuming that non-anemic individuals maintain sufficient iron stores. However, the trial confirms that cellular iron deficiency impairs physical capacity regardless of hemoglobin status. Accordingly, physicians should routinely screen every symptomatic heart failure patient using both serum ferritin and transferrin saturation. When laboratory testing confirms iron deficiency, clinicians should promptly administer intravenous iron rather than ineffective oral tablets. In addition, delivering a single 1,000-mg dose of ferric derisomaltose ensures complete adherence while avoiding troublesome gastrointestinal side effects. Looking forward, ongoing international phase III studies, including the ICONIC-HF trial, will evaluate whether routine iron replenishment reduces cardiovascular hospitalizations and mortality. Moreover, combining intravenous iron with modern disease-modifying agents, such as sodium-glucose cotransporter-2 inhibitors, may yield synergistic metabolic benefits. Ultimately, proactive iron screening and targeted repletion provide an accessible, effective therapeutic strategy for improving functional vitality in preserved ejection fraction.

Frequently Asked Questions

How do clinicians diagnose iron deficiency in patients with HFpEF?

Clinicians diagnose iron deficiency in heart failure by assessing both serum ferritin concentration and transferrin saturation. Specifically, diagnostic criteria define iron deficiency as a serum ferritin level below 100 ng/mL, or a ferritin concentration between 100 and 299 ng/mL when transferrin saturation is under 20%. Importantly, healthcare providers must evaluate these biomarkers regardless of whether anemia is present, because cellular iron deficiency frequently impairs exercise capacity even when hemoglobin concentrations remain normal.

Why is intravenous iron preferred over oral iron in heart failure?

Intravenous iron is strongly preferred because chronic heart failure triggers systemic inflammation that elevates circulating hepcidin levels. Consequently, increased hepcidin blocks intestinal ferroportin channels, severely preventing oral iron absorption across the gastrointestinal mucosa. Furthermore, oral iron supplements regularly cause adverse gastrointestinal symptoms, leading to high discontinuation rates. In contrast, intravenous ferric derisomaltose bypasses the gut completely, rapidly delivers therapeutic doses directly into the bloodstream, and effectively replenishes exhausted muscular and mitochondrial iron reserves.

What clinical improvements were demonstrated in the IRONMET-HFpEF trial?

The IRONMET-HFpEF trial demonstrated that a single 1,000-mg infusion of ferric derisomaltose achieved a statistically significant 10% increase in peak oxygen uptake at 12 weeks compared to baseline. Moreover, active treatment led to a significant 41.1-meter improvement in the six-minute walk test relative to placebo. These findings confirm that replenishing cellular iron stores enhances both objective cardiorespiratory performance and functional endurance, directly mitigating the debilitating physical limitations common in preserved ejection fraction.

Disclaimer: This content is for informational and educational purposes only... Refer to the latest local and national guidelines for clinical practice.

References

Lewis GD et al. Iron Repletion in Heart Failure With Preserved Ejection Fraction: The IRONMET-HFpEF Randomized Trial. Circulation. 2026 Nov 08. doi: 10.1161/CIRCULATIONAHA.126.084009. PMID: 42999950.

Kalra PR, Cleland JGF, Petrie MC, et al. Intravenous ferric derisomaltose in patients with heart failure and iron deficiency in the UK (IRONMAN): an investigator-initiated, prospective, randomised, open-label, blinded-endpoint trial. Lancet. 2022;400(10369):2199-2209.

McDonagh T, Metra M, Adamo M, et al. 2023 Focused Update of the 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. Eur Heart J. 2023;44(37):3627-3639.

Lewis GD, Malhotra R, Hernandez AF, et al. Effect of Oral Iron Repletion on Exercise Capacity in Patients With Heart Failure With Reduced Ejection Fraction and Iron Deficiency: The IRONOUT HF Randomized Clinical Trial. JAMA. 2017;317(19):1958-1966.