Rationale: Pulmonary arterial hypertension (PAH) is a life-threatening progressive cardiopulmonary disease associated with high morbidity and mortality. Changes in the six-minute walk test (6MWT) provide prognostic information and help guide treatment decisions for PAH. However, since 6MWT requires in-clinic visits, clinical interventions to address disease progression may be delayed. Wearable technologies could reduce this delay by allowing the performance of 6MWT in the community and delivering data to clinicians remotely. Objectives: To perform a pilot study to determine the safety and feasibility of performing 6MWT in PAH outpatients using a wearable app-based tool. Methods: PAH patients recruited at Stanford University were provided an Apple Watch with an app to perform daily, self-administered 6MWT over 12 weeks. Bland-Altman plots and correlations were used to assess the agreement and reliability of in-clinic vs. app-based 6MWT data at the beginning and end of the 12-week trial. Measurements and Main Results: From 55 PAH participants, we collected 3,139 app-recorded walks during 979.7 patient-weeks of exposure. On average, participants performed 3±2.3 weekly walks. No serious adverse events were reported. App-derived walk distance was highly correlated (r ≥ 0.9) to the baseline in-clinic 6MWD and showed excellent reliability (ICC=0.9). Correlation and agreement were significantly lower at the 12-week follow-up visit. App-derived metrics beyond 6MWD showed promising associations with disease status. Conclusions: App-based outpatient 6MWT is feasible, safe, reasonably accurate, likely clinically relevant, and reliable in PAH patients but long-term measurement stability may be a concern. App-derived digital measures beyond distance show promise for future applications.

The authors have declared no competing interest.

NCT03893500

Stanford University received partial funding from the non-profit organization PHaware Global Association to conduct this study. NS received funding from the Swiss National Science Foundation under the Postdoc.Mobility fellowship 210803. The Stanford REDCap platform (http://redcap.stanford.edu) is developed and operated by Stanford Medicine Research Technology team. The REDCap platform services at Stanford are subsidized by a) Stanford School of Medicine Research Office, and b) the National Center for Research Resources and the National Center for Advancing Translational Sciences, National Institutes of Health, through grant UL1 TR001085.

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