The goal of this observational study is to develop longitudinal multimarker risk models for decision support during the clinical follow-up of very elderly patients with heart failure and preserved ejection fraction (HFpEF).

The main questions it aims to answer are:

• Can advanced risk prediction models accurately estimate the prognosis of very elderly patients with HFpEF over a 1-year follow-up after a hospitalization for acute heart failure?
• Do novel biomarkers, in addition to routine clinical variables and elderly-specific predictors, contribute to improved risk prediction for these patients?

To this end, very elderly patients (aged 80 or older) who have HFpEF and were admitted for acute heart failure will be included. Clinical and biological data will be collected during their hospitalization and also during follow-up visits 30 and 90 days after discharge.

There is no comparison group in this observational study.

Background: Very elderly patients with heart failure and preserved ejection fraction (HFpEF) are under-represented in risk prediction models, and the role of prognostic biomarkers in this population is unclear due to the presence of cumulative comorbidity burden. Risk prediction is a useful tool to support decision making across the clinical follow-up of very elderly HFpEF patients.

Aim: To develop longitudinal prognostic models based on readily available clinical and biological variables, novel biomarkers and elderly-specific predictors to estimate prognosis over 1-year follow-up after a HF hospitalization in very elderly patients with HFpEF.

Design: Observational, single-centre, prospective cohort study of very elderly patients (≥80 years old) with HFpEF consecutively admitted for acute HF.

Main outcome: Composite of 1-year all-cause mortality and/or HF-hospitalization. Sample size: 184 patients.

Follow-up time: 1 year. Predictors: Routine clinical variables (sociodemographic, medical history, physical examination, vital signs, laboratory tests, imaging, concomitant medication, quality of life and elderly-specific factors) and novel biomarkers will be longitudinally collected during index hospitalization, 30-day and 90-day post-discharge visits.

Statistical analysis: Kaplan-meier survival analysis. Logistic and Cox proportional-hazards regression models, time-to-event models for repeated events, linear-mixed effects, joint models, LASSO and machine learning techniques will be used for model development.

Inclusion Criteria:

1. age ≥80 years;
2. diagnosis of HFpEF, requiring the 4 following conditions: b1) typical symptoms and/or signs of HF; b2) left ventricular ejection fraction (LVEF) ≥50%; b3) elevated levels of natriuretic peptides (NTproBNP ≥300 pg/mL or BNP ≥100 pg/mL in sinus rhythm; NT-proBNP ≥900 pg/mL or BNP ≥300 pg/mL in atrial fibrillation); and b4) at least one additional criterion: b4.1) relevant structural heart disease (left ventricular hypertrophy and/or left atrial enlargement), or 4.2) diastolic dysfunction;
3. hospitalization with a primary diagnosis of acute HF; and
4. giving informed consent.

Exclusion Criteria:

1. any clinical condition, such as HF secondary to congenital heart disease and severe valve disease, severe renal (requiring dialysis) and liver disease, active malignant diseases, autoimmune diseases, other diseases resulting in <1-year life expectancy or any other condition that, according to investigators' criteria, could significantly interfere with the study objectives;
2. any clinical or social condition that prevents clinical follow-up.

Very elderly patients (≥80 years old) with HFpEF consecutively admitted for acute HF at Hospital Universitario Ramón y Cajal and followed up at Unit of Heart Failure (UICA) of the Internal Medicine Dept.

After the end of the project, the generated dataset and the metadata file will be deposited in an open data repository, complying with open science criteria - FAIR.

Moreover, study documentation, including study protocol, statistical analysis and informed consent form will be shared openly.

From 1 year after the end of the project and for at least 5 years.

IPD will be available to stakeholders, authorities, ethics committees and other parties legitimately interested in verifying their proper treatment and management.

IPD may be used to ensure the scientific quality of the project results. That is to say, to carry out reproducibility of the results, if necessary at the request of scientific publication entities, among others, with prior authorization from the Research Ethics Committee, they may be reused for new research projects, provided that the consent collected allows it and/or in accordance with the applicable laws on data protection.