*Purpose: Monitoring for acute rejection (AR) after orthotopic heart transplantation (OHTx) is primarily achieved by evaluating histological endomyocardial biopsies (EMBx). However, this procedure is limited by its invasive nature, low sensitivity for early detection, and high interobserver variability in histological grading. Immunosuppressive regimens are essential for anti-rejection management but also increase the risk for infection and post-transplant lymphoproliferative disorder. Smartwatch technologies may supplement routine surveillance of both AR and infection.

*Methods: This two-phased, prospective study recruited pediatric OHTx recipients to assess the utility of smartwatch-derived biometric data for rejection and infection detection. Household members were enrolled as non-Tx controls. All subjects receive FitBit or Sensomics devices for remote monitoring of biometric data (heart rate, heart rate variability, oxygen saturation, activity levels, and sleep patterns). The My Personal Health Dashboard (MyPHD) app is used to integrate secure data transfer, collection of daily health questionnaires, and real-time analysis using proprietary algorithms. During the initial 30+ day period, healthy baseline metrics are established (Phase 1). Subsequently, subjects transition into an interventional phase with real-time detection through an alerting system to assess sustained deviations from baseline, followed by discussions and potential recommendations from the clinical team (Phase 2). The collected biometrics are also contemporaneously cross-evaluated with ISHLT histological grading of surveillance and for-cause EMBxs.

*Results: A total of 36 OHTx recipients (ages 2-21 years) and 110 household members have been recruited since April 2021. Phase 1 is ongoing, with Phase 2 set to commence May 2022. Over 100,000 biometric readings per day per individual are processed through quality control pipelines and incorporated with key electronic medical record data including lab and other variables related to acute rejection and infection related phenotypes/outcomes. Before May 2022, it is expected that ~11 infections/events will occur.

*Conclusions: By providing real-time access to physiological data, wearable technology has the potential to enhance routine clinical surveillance of OHTx recipients and allow for earlier detection of acute rejection and infection.

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