The aim of our study is to understand the biological pathways involved in the occurrence of IDy in patients with HF since ID is very common and supposes a negative impact in terms of clinical outcomes in these patients. In this context, a deeper understanding of the mechanisms involved in the development of ID in these patients and the impact on the altered biological pathways after iron replenishment will pave the way for an improvement and simplification of the preventive strategies in patients with HF.

The IRON-PATH II Project is a pre-clinical and clinical study designed as a multicenter, prospective, observational (non-interventional), investigator initiated study. The total number of patients to be recruited will be 210 (80 patients without ID and 130 patients with ID). Patients will be recruited during 12 months in 7 centers across Spain and Portugal and followed for a fixed period of 12 months. The primary objective of the clinical study is to define pathways associated with systemic and tissue ID in HF patients compared with non-ID HF patients and explore the change in the patterns of pathway activation/suppression after irons status normalization in ID patients with intravenous iron treatment using an integrative omics and systems biology approach including whole-genome analysis of gene expression (transcriptome), protein synthesis (proteomics) and metabolic characterization (metabolomics) from blood samples. Key secondary objectives will include changes in patient-reported outcomes (PROMs) such as QoL, patient-reported experience measures (PREMs), the occurrence of events, among others between those with and without ID. The aims of the pre-clinical study is to confirm previous findings of the IRONPATH I study and to explore in vitro interventions in cardiac cells models with iron deficiency.

Inclusion Criteria:

• Age ≥ 18 years old.
• HF diagnosis according to European Society of Cardiology
• LVEF≤50% (systolic HF).
• Patients receiving oral standard medication for chronic HF.
• Iron status evaluated in the last 3 months.
• Written informed consent.

Exclusion Criteria:

• Age<18 years old.
• Intravenous or oral iron administration or under treatment with ESA (erythropoiesis-stimulating agents) in the previous 3 months.
• Planned cardiac resynchronization therapy (CRT), revascularization and other major interventions including heart transplant or left ventricular assist device (LVAD) implantation in the next 3 months in patients with ID.
• Planned uptitration of guideline-mandatory HF-modifying drugs in the next 3 months (except iron repletion) in patients with ID.
• Moderate or severe anaemia (Hb<11 g/dL).
• The patient is unable or unwilling to give the informed consent to participate.
• Unstable patients with signs of fluid overload or low cardiac output at the moment of enrollment.
• Life expectancy less than 1 year (excluding HF).
• The patient is considered not to be an adequate candidate for this study according to the decision of the local investigator.

The study cohort will be a multicenter, observational, prospective, cross-sectional and longitudinal nested case-control sample of 210 patients with (130 cases) and without (80 controls) ID according to the FAIR-HF (27) (serum ferritin <100 mg/L or transferrin saturation [%TSAT]<20% if ferritin is between 100-300mg/L), recruited for the specific purpose of the IRON-PATH II study.