Authors:

T Proesmans¹ , F Verbrugge² , J Vijgen³ , W Mullens² , M Rivero-Ayerza² , H Van Herendael² , P Vandervoort² , D Nuyens² , ¹Hasselt University, Mobile Health Unit - Diepenbeek - Belgium , ²Hospital Oost-Limburg (ZOL) - Genk - Belgium , ³Virga Jesse Hospital - Hasselt - Belgium ,

Introduction
Pulse-deriving smartphone applications have the potential to aid in the detection of atrial fibrillation. However, questions concerning their diagnostic capabilities, applicability in the relevant populations, and robustness remain to be answered.

Objective
This observational study evaluated the applicability and robustness of a pulse-deriving smartphone application implemented in a broad population in a free-living setting.

Methods
A local newspaper published a free 7-day access code for a pulse-deriving smartphone application. Participants to this screening program received instructions on how to perform high quality measurements twice daily. To obtain a high quality signal, participants were instructed to adopt a sitting position with both arms resting on a firm surface, holding the smartphone in a vertical position with their dominant hand. Subsequently, the index finger of their non dominant hand should cover the flashlight and backside camera horizontally, without putting firm pressure

The smartphone application used in this study firstly checks acquired PPG signals for their quality. Compromised signals are not used for analysis to avoid inaccurate diagnostic results. Study participants with frequent poor quality PPG measurements received notifications through the application, guiding them on how to perform better measurements.

Results
From 12,328 readers who voluntarily signed up for screening (49±14 years; 58% men), 120,446 unique PPG traces were obtained. AF was detected in 136 individuals (1.1%).

PPG signal quality was sufficient for analysis in 110,713 measurements (92%). The frequency of measurements with insufficient quality for analysis decreased significantly during the screening period, from 17% on day 1 to 2% on day 7 (P-value<0.001), indicating a steep learning curve.  8,683 participants only performed high quality PPG measurements. They were significantly younger compared to participants with at least one insufficient quality measurement (49 versus 51 years old, P-value<0.001).

Conclusion
This study demonstrates the applicability and robustness of a pulse-deriving smartphone application in a broad population in an unsupervised setting, provided that efforts are focused on training and education. Awaiting further validation studies, these results indicate the potential of a pulse-deriving smartphone application to detect atrial fibrillation.