A study into cardiac health being carried out by Stanford University and Apple, using the Apple Watch to track wearers heartbeat and other health metrics, has attracted over 400,000 participants. The study, which closed to new participants in August, has entered the “final phase of data collection” and is expected to be completed in early 2019.

“We hope this study will help us better understand how wearable technologies can inform precision health,” said Dr Lloyd Minor, dean of the School of Medicine at Stanford University. “These new tools, which have the potential to predict, prevent and manage disease, are finally within our reach.”

The primary focus of the study is to determine whether wearable technology can detect irregular heart rhythms which suggest atrial fibrillation, a heart-rhythm disorder that can increase the risk of stroke and heart failure. Because the symptoms are rarely detected by people with the problem, the condition often remains hidden until it results in major health problems.

Enrollment in the study was carried out through an accompanying iOS app, which also intermittently checks the heart-rate pulse sensor for measurements of an irregular pulse. If sufficient episodes of an irregular pulse are detected, then the participant receives a notification and is asked to schedule a visit with a doctor involved in the study.

“We are inspired by the overwhelming response to the Apple Heart Study,” said Dr Sumbul Desai, vice president in Apples health team. “Through the combined power of our participants, Apple Watch and Stanford Medicine, its one of the largest and most novel atrial fibrillation studies to date.”

Apple now has two Apple Watch apps cleared by the US Food and Drug Administration. One app uses data from new hardware on the Apple Watch Series 4 to take an electrocardigram by touching the button on the side of the device. The other, used in this study, uses data from an optical sensor available on the Apple Watch Series 1 and later to analyse pulse data to identify irregular heartbeats.