The Silicon Valley company first offered an ECG service on its Apple Watch Series 4 last year.
But doctors have previously expressed concerns about the accuracy of the technology and have urged its use to be in tandem with proper consultation.
According to the NHS, atrial fibrillation affects around 1m people in the UK and can affect adults of any age. Researchers concluded the study’s data could be used as an additional tool by doctors diagnosing patients.
“The physician can use the information from the study, combine it with their assessment…. And then guide clinical decisions around what to do with an alert,” said Stanford University’s Dr Marco Perez, a lead investigator on the study.