Three years after the original Apple Watch launched with a heart rate monitor, Apple dramatically improved the cardiovascular functionality by adding electrocardiogram recording to the Apple Watch Series 4. Now the company will partner with Johnson & Johnson’s Janssen Pharmaceuticals unit to study whether the wearable can also be used to prevent strokes.

The study appears to be focusing on the latest Apple Watch’s ability to detect atrial fibrillation (AFib) earlier than prior models, which might enable the Series 4 model to suss out a leading cause of strokes. Apple added occasional background checks for AFib to Series 1 through 3 models last December, relying on the results of five heart rhythm readings, but the new Apple Watch might be able to provide better and faster warning.

Johnson & Johnson chief scientific officer Paul Stoffels explained that “the goal is to identify early on AFib and prevent stroke by combining the physical know-how from Apple and what we have from the medical and scientific know-how.”

“We are receiving thank you letters daily from Apple Watch wearers who are discovering they have AFib,” said Apple COO Jeff Williams. “We want a deeper understanding about outcomes and prevention associated with early detection. We are excited to work with Johnson & Johnson, which has a long history and expertise in cardiovascular disease.”

While the “release hardware first, determine what it can do later” strategy can be somewhat confusing for users, studies such as this are all but necessary in the world of medical devices. Just as with medicines that receive approval for one purpose but are later discovered to be useful in treating another ailment, mass, semi-public testing with a specific and proven positive outcome is generally required before a device can be marketed for a medical purpose.

According to the companies, the Apple Watch stroke prevention study will begin later this year and run for multiple years, which is to say that a stroke prevention feature is unlikely to appear in the next year or two. Participants will solely be testing a Johnson & Johnson-developed app on the Apple Watch Series 4, and must be at least 65 years old. The companies will release additional details on how to participate alongside the app.

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