Abstract Body (Do not enter title and authors here): Introduction: Guideline-directed medical therapy (GDMT) for Heart Failure with reduced ejection fraction (HFrEF) reduces adverse events by 70%, but is underutilized. The Human Centered Design (HCD) methodology can be useful to build a strategy to optimize GDMT centered on patients’ demands and perspectives. We aimed to reciprocally innovate a telephone-based digital health intervention (DHI) from a Brazilian trial to an app co-developed for a US trial and iterate it again to the Brazilian context using HCD. We will evaluate the app’s usability and utility to facilitate HF GDMT optimization, considering barriers of the Brazilian public health system users, such as low literacy and socioeconomic status.

Methods: Mixed methods study. Steps were carried out according to HCD method: (1) empathizing and identifying challenges, (2) suggesting solutions, (3) prototype development, (4) ranking features for feasibility and utility (5) engineering work and (6) prototype testing. In stages 1-3, semi-structured interviews were held with 10 HF patients and 2 health professionals. Steps 4 and 5 were done by the research team. In stage 6, we conducted a pilot study with 10 HFrEF patients, with at least one GDMT drug with an optimization gap. The primary outcome was the app’s usability assessed by an engagement score, and the app’s utility at 4 weeks. Secondary outcomes included change in self-care score using the European Self-Care Behavior Scale. After step 6, new interviews were carried out to capture the user experience and identify new iterations. Interviews were recorded and transcribed for content analysis.

Results: The average engagement score was 80% (SD 16) and the app’s utility score was 82% (SD 8). The average self-care score increased by 32% (SD 25) at the end of the pilot. The main challenges were lack of knowledge about HF and self-care. Technical difficulties and lack of trust in the app to handle health data were mentioned. In the pilot, patients reported the app was easy to use and contributed to self-care and understanding of HF. Among the DHI components, teleconsultation was best evaluated, followed by the educational videos. The greatest challenge was connecting the blood pressure cuff and scale via Bluetooth.

Conclusion: The app was well accepted and considered useful by patients. User contributions were fundamental to create tools that facilitate engagement and utility. The final product will be evaluated in a randomized, multicenter, clinical trial.