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When the Food and Drug Administration cleared Apple’s smartwatch app that alerts people if they may be at risk of an irregular heart rhythm called atrial fibrillation, scientists had one big question — how good is it?

Only a bit of data has been released about the device. In September, the FDA told STAT that the company collected much of the data supporting the app during its Heart Study, a nearly yearlong clinical trial it funded, based at Stanford University.


On Thursday, the American Heart Journal published the protocol for that trial, describing the eligibility criteria, recruitment patterns, procedures, data collected, and the study’s endpoints.

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