An app notification thanked them for their participation and asked them to complete an exit-survey about the study, which first launched in November 2017.
The study in collaboration with Stanford Medicine was offered to anyone in the United States who was 22 years older with an iPhone 5s or later and an Apple Watch Series 1 or later. Atrial fibrillation, a common form of heart arrhythmia that is covered in the study, can indicate serious medical conditions like heart failure and stroke.
Participants were instructed to download and install the Apple Heart Study app and wear their Apple Watch. When an irregular heart beat is detected, a consultation with a Study Telehealth provider from American Well is offered, with some people asked to wear an ePatch monitor for up to seven days for further investigation.
Apple closed the study to new participants at the beginning of last month. In a prior announcement, Apple said the study would not end until January 1, 2019, but it looks as though the participants who received the notifications over the weekend all enrolled early, suggesting that data collection is winding down over stages as the end date approaches.
Rumors have suggested that 2018 Apple Watch Series 4 models will include enhanced heart rate detection features that could improve the smartwatch's ability to detect diseases linked to higher heart rates and abnormal heart rhythms, but what form the enhanced heart rate features will take remains unclear.
Design wise, the Apple Watch Series 4 looks similar to the Series 3 models, but the display will be bigger, allowing more space for watch faces and complications, as confirmed last week in an image leaked by Apple.